From 1531d6e5439daae01627b2645684876b75eaf5eb Mon Sep 17 00:00:00 2001
From: romkatv <roman.perepelitsa@gmail.com>
Date: Sun, 10 May 2020 15:58:05 +0200
Subject: Squashed 'gitstatus/' content from commit 6b9ba17

git-subtree-dir: gitstatus
git-subtree-split: 6b9ba179c6655286c4c399e7926d5098dd6bd706
---
 src/algorithm.h        |  37 ++++
 src/arena.cc           | 118 ++++++++++++
 src/arena.h            | 273 +++++++++++++++++++++++++++
 src/bits.h             |  29 +++
 src/check.h            |  61 ++++++
 src/check_dir_mtime.cc | 157 +++++++++++++++
 src/check_dir_mtime.h  |  31 +++
 src/dir.cc             | 234 +++++++++++++++++++++++
 src/dir.h              |  50 +++++
 src/git.cc             | 242 ++++++++++++++++++++++++
 src/git.h              | 106 +++++++++++
 src/gitstatus.cc       | 210 +++++++++++++++++++++
 src/index.cc           | 455 ++++++++++++++++++++++++++++++++++++++++++++
 src/index.h            |  84 +++++++++
 src/logging.cc         | 139 ++++++++++++++
 src/logging.h          | 124 ++++++++++++
 src/options.cc         | 342 +++++++++++++++++++++++++++++++++
 src/options.h          |  76 ++++++++
 src/print.h            | 101 ++++++++++
 src/repo.cc            | 503 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/repo.h             | 126 +++++++++++++
 src/repo_cache.cc      | 167 ++++++++++++++++
 src/repo_cache.h       |  60 ++++++
 src/request.cc         | 130 +++++++++++++
 src/request.h          |  50 +++++
 src/response.cc        |  73 +++++++
 src/response.h         |  50 +++++
 src/scope_guard.h      |  56 ++++++
 src/serialization.h    |  28 +++
 src/stat.h             |  23 +++
 src/string_cmp.h       | 151 +++++++++++++++
 src/string_view.h      |  77 ++++++++
 src/strings.cc         |  71 +++++++
 src/strings.h          |  37 ++++
 src/tag_db.cc          | 311 ++++++++++++++++++++++++++++++
 src/tag_db.h           |  79 ++++++++
 src/thread_pool.cc     |  87 +++++++++
 src/thread_pool.h      |  74 ++++++++
 src/time.h             |  14 ++
 src/timer.cc           |  72 +++++++
 src/timer.h            |  36 ++++
 src/tribool.h          |  27 +++
 42 files changed, 5171 insertions(+)
 create mode 100644 src/algorithm.h
 create mode 100644 src/arena.cc
 create mode 100644 src/arena.h
 create mode 100644 src/bits.h
 create mode 100644 src/check.h
 create mode 100644 src/check_dir_mtime.cc
 create mode 100644 src/check_dir_mtime.h
 create mode 100644 src/dir.cc
 create mode 100644 src/dir.h
 create mode 100644 src/git.cc
 create mode 100644 src/git.h
 create mode 100644 src/gitstatus.cc
 create mode 100644 src/index.cc
 create mode 100644 src/index.h
 create mode 100644 src/logging.cc
 create mode 100644 src/logging.h
 create mode 100644 src/options.cc
 create mode 100644 src/options.h
 create mode 100644 src/print.h
 create mode 100644 src/repo.cc
 create mode 100644 src/repo.h
 create mode 100644 src/repo_cache.cc
 create mode 100644 src/repo_cache.h
 create mode 100644 src/request.cc
 create mode 100644 src/request.h
 create mode 100644 src/response.cc
 create mode 100644 src/response.h
 create mode 100644 src/scope_guard.h
 create mode 100644 src/serialization.h
 create mode 100644 src/stat.h
 create mode 100644 src/string_cmp.h
 create mode 100644 src/string_view.h
 create mode 100644 src/strings.cc
 create mode 100644 src/strings.h
 create mode 100644 src/tag_db.cc
 create mode 100644 src/tag_db.h
 create mode 100644 src/thread_pool.cc
 create mode 100644 src/thread_pool.h
 create mode 100644 src/time.h
 create mode 100644 src/timer.cc
 create mode 100644 src/timer.h
 create mode 100644 src/tribool.h

(limited to 'src')

diff --git a/src/algorithm.h b/src/algorithm.h
new file mode 100644
index 00000000..b87b13f0
--- /dev/null
+++ b/src/algorithm.h
@@ -0,0 +1,37 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_ALGORITHM_H_
+#define ROMKATV_GITSTATUS_ALGORITHM_H_
+
+#include <algorithm>
+
+namespace gitstatus {
+
+// Requires: Iter is a BidirectionalIterator.
+//
+// Returns iterator pointing to the last value in [begin, end) that compares equal to the value, or
+// begin if none compare equal.
+template <class Iter, class T>
+Iter FindLast(Iter begin, Iter end, const T& val) {
+  while (begin != end && !(*--end == val)) {}
+  return end;
+}
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_ALGORITHM_H_
diff --git a/src/arena.cc b/src/arena.cc
new file mode 100644
index 00000000..4c137639
--- /dev/null
+++ b/src/arena.cc
@@ -0,0 +1,118 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "arena.h"
+
+#include <algorithm>
+#include <type_traits>
+
+#include "bits.h"
+#include "check.h"
+
+namespace gitstatus {
+
+namespace {
+
+size_t Clamp(size_t min, size_t val, size_t max) { return std::min(max, std::max(min, val)); }
+
+static const uintptr_t kSingularity = reinterpret_cast<uintptr_t>(&kSingularity);
+
+}  // namespace
+
+// Triple singularity. We are all fucked.
+Arena::Block Arena::g_empty_block = {kSingularity, kSingularity, kSingularity};
+
+Arena::Arena(Arena::Options opt) : opt_(std::move(opt)), top_(&g_empty_block) {
+  CHECK(opt_.min_block_size <= opt_.max_block_size);
+}
+
+Arena::Arena(Arena&& other) : Arena() { *this = std::move(other); }
+
+Arena::~Arena() {
+  // See comments in Makefile for the reason sized deallocation is not used.
+  for (const Block& b : blocks_) ::operator delete(reinterpret_cast<void*>(b.start));
+}
+
+Arena& Arena::operator=(Arena&& other) {
+  if (this != &other) {
+    // In case std::vector ever gets small object optimization.
+    size_t idx = other.reusable_ ? other.top_ - other.blocks_.data() : 0;
+    opt_ = other.opt_;
+    blocks_ = std::move(other.blocks_);
+    reusable_ = other.reusable_;
+    top_ = reusable_ ? blocks_.data() + idx : &g_empty_block;
+    other.blocks_.clear();
+    other.reusable_ = 0;
+    other.top_ = &g_empty_block;
+  }
+  return *this;
+}
+
+void Arena::Reuse(size_t num_blocks) {
+  reusable_ = std::min(reusable_, num_blocks);
+  for (size_t i = reusable_; i != blocks_.size(); ++i) {
+    const Block& b = blocks_[i];
+    // See comments in Makefile for the reason sized deallocation is not used.
+    ::operator delete(reinterpret_cast<void*>(b.start));
+  }
+  blocks_.resize(reusable_);
+  if (reusable_) {
+    top_ = blocks_.data();
+    top_->tip = top_->start;
+  } else {
+    top_ = &g_empty_block;
+  }
+}
+
+void Arena::AddBlock(size_t size, size_t alignment) {
+  if (alignment > alignof(std::max_align_t)) {
+    size += alignment - 1;
+  } else {
+    size = std::max(size, alignment);
+  }
+  if (size <= top_->size() && top_ < blocks_.data() + reusable_ - 1) {
+    assert(blocks_.front().size() == top_->size());
+    ++top_;
+    top_->tip = top_->start;
+    return;
+  }
+  if (size <= opt_.max_alloc_threshold) {
+    size =
+        std::max(size, Clamp(opt_.min_block_size, NextPow2(top_->size() + 1), opt_.max_block_size));
+  }
+
+  auto p = reinterpret_cast<uintptr_t>(::operator new(size));
+  blocks_.push_back(Block{p, p, p + size});
+  if (reusable_) {
+    if (size < blocks_.front().size()) {
+      top_ = &blocks_.back();
+      return;
+    }
+    if (size > blocks_.front().size()) reusable_ = 0;
+  }
+  std::swap(blocks_.back(), blocks_[reusable_]);
+  top_ = &blocks_[reusable_++];
+}
+
+void* Arena::AllocateSlow(size_t size, size_t alignment) {
+  assert(alignment && !(alignment & (alignment - 1)));
+  AddBlock(size, alignment);
+  assert(Align(top_->tip, alignment) + size <= top_->end);
+  return Allocate(size, alignment);
+}
+
+}  // namespace gitstatus
diff --git a/src/arena.h b/src/arena.h
new file mode 100644
index 00000000..0bad0bfa
--- /dev/null
+++ b/src/arena.h
@@ -0,0 +1,273 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_ARENA_H_
+#define ROMKATV_GITSTATUS_ARENA_H_
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <limits>
+#include <new>
+#include <type_traits>
+#include <vector>
+
+#include "string_view.h"
+
+namespace gitstatus {
+
+// Thread-compatible. Very fast and very flexible w.r.t. allocation size and alignment.
+//
+// Natural API extensions:
+//
+//   // Donates a block to the arena. When the time comes, it'll be freed with
+//   // free(p, size, userdata).
+//   void Donate(void* p, size_t size, void* userdata, void(*free)(void*, void*));
+class Arena {
+ public:
+  struct Options {
+    // The first call to Allocate() will allocate a block of this size. There is one exception when
+    // the first requested allocation size is larger than this limit. Subsequent blocks will be
+    // twice as large as the last until they saturate at max_block_size.
+    size_t min_block_size = 64;
+
+    // Allocate blocks at most this large. There is one exception when the requested allocation
+    // size is larger than this limit.
+    size_t max_block_size = 8 << 10;
+
+    // When the size of the first allocation in a block is larger than this threshold, the block
+    // size will be equal to the allocation size. This is meant to reduce memory waste when making
+    // many allocations with sizes slightly over max_block_size / 2. With max_alloc_threshold equal
+    // to max_block_size / N, the upper bound on wasted memory when making many equally-sized
+    // allocations is 100.0 / (N + 1) percent. When making allocations of different sizes, the upper
+    // bound on wasted memory is 50%.
+    size_t max_alloc_threshold = 1 << 10;
+
+    // Natural extensions:
+    //
+    //   void* userdata;
+    //   void (*alloc)(size_t size, size_t alignment, void* userdata);
+    //   void (*free)(size_t size, void* userdata);
+  };
+
+  // Requires: opt.min_block_size <= opt.max_block_size.
+  //
+  // Doesn't allocate any memory.
+  Arena(Options opt);
+  Arena() : Arena(Options()) {}
+  Arena(Arena&&);
+  ~Arena();
+
+  Arena& operator=(Arena&& other);
+
+  // Requires: alignment is a power of 2.
+  //
+  // Result is never null and always aligned. If size is zero, the result may be equal to the last.
+  // Alignment above alignof(std::max_align_t) is supported. There is no requirement for alignment
+  // to be less than size or to divide it.
+  inline void* Allocate(size_t size, size_t alignment) {
+    assert(alignment && !(alignment & (alignment - 1)));
+    uintptr_t p = Align(top_->tip, alignment);
+    uintptr_t e = p + size;
+    if (e <= top_->end) {
+      top_->tip = e;
+      return reinterpret_cast<void*>(p);
+    }
+    return AllocateSlow(size, alignment);
+  }
+
+  template <class T>
+  inline T* Allocate(size_t n) {
+    static_assert(!std::is_reference<T>(), "");
+    return static_cast<T*>(Allocate(n * sizeof(T), alignof(T)));
+  }
+
+  template <class T>
+  inline T* Allocate() {
+    return Allocate<T>(1);
+  }
+
+  inline char* MemDup(const char* p, size_t len) {
+    char* res = Allocate<char>(len);
+    std::memcpy(res, p, len);
+    return res;
+  }
+
+  // Copies the null-terminated string (including the trailing null character) to the arena and
+  // returns a pointer to the copy.
+  inline char* StrDup(const char* s) {
+    size_t len = std::strlen(s);
+    return MemDup(s, len + 1);
+  }
+
+  // Guarantees: !StrDup(p, len)[len].
+  inline char* StrDup(const char* p, size_t len) {
+    char* res = Allocate<char>(len + 1);
+    std::memcpy(res, p, len);
+    res[len] = 0;
+    return res;
+  }
+
+  // Guarantees: !StrDup(s)[s.len].
+  inline char* StrDup(StringView s) {
+    return StrDup(s.ptr, s.len);
+  }
+
+  template <class... Ts>
+  inline char* StrCat(const Ts&... ts) {
+    return [&](std::initializer_list<StringView> ss) {
+      size_t len = 0;
+      for (StringView s : ss) len += s.len;
+      char* p = Allocate<char>(len + 1);
+      for (StringView s : ss) {
+        std::memcpy(p, s.ptr, s.len);
+        p += s.len;
+      }
+      *p = 0;
+      return p - len;
+    }({ts...});
+  }
+
+  // Copies/moves `val` to the arena and returns a pointer to it.
+  template <class T>
+  inline std::remove_const_t<std::remove_reference_t<T>>* Dup(T&& val) {
+    return DirectInit<std::remove_const_t<std::remove_reference_t<T>>>(std::forward<T>(val));
+  }
+
+  // The same as `new T{args...}` but on the arena.
+  template <class T, class... Args>
+  inline T* DirectInit(Args&&... args) {
+    T* res = Allocate<T>();
+    ::new (const_cast<void*>(static_cast<const void*>(res))) T(std::forward<Args>(args)...);
+    return res;
+  }
+
+  // The same as `new T(args...)` but on the arena.
+  template <class T, class... Args>
+  inline T* BraceInit(Args&&... args) {
+    T* res = Allocate<T>();
+    ::new (const_cast<void*>(static_cast<const void*>(res))) T{std::forward<Args>(args)...};
+    return res;
+  }
+
+  // Tip() and TipSize() allow you to allocate the remainder of the current block. They can be
+  // useful if you are flexible w.r.t. the allocation size.
+  //
+  // Invariant:
+  //
+  //   const void* tip = Tip();
+  //   void* p = Allocate(TipSize(), 1);  // grab the remainder of the current block
+  //   assert(p == tip);
+  const void* Tip() const { return reinterpret_cast<const void*>(top_->tip); }
+  size_t TipSize() const { return top_->end - top_->tip; }
+
+  // Invalidates all allocations (without running destructors of allocated objects) and frees all
+  // blocks except at most the specified number of blocks. The retained blocks will be used to
+  // fulfil future allocation requests.
+  void Reuse(size_t num_blocks = std::numeric_limits<size_t>::max());
+
+ private:
+  struct Block {
+    size_t size() const { return end - start; }
+    uintptr_t start;
+    uintptr_t tip;
+    uintptr_t end;
+  };
+
+  inline static size_t Align(size_t n, size_t m) { return (n + m - 1) & ~(m - 1); };
+
+  void AddBlock(size_t size, size_t alignment);
+  bool ReuseBlock(size_t size, size_t alignment);
+
+  __attribute__((noinline)) void* AllocateSlow(size_t size, size_t alignment);
+
+  Options opt_;
+  std::vector<Block> blocks_;
+  // Invariant: !blocks_.empty() <= reusable_ && reusable_ <= blocks_.size().
+  size_t reusable_ = 0;
+  // Invariant: (top_ == &g_empty_block) == blocks_.empty().
+  // Invariant: blocks_.empty() || top_ == &blocks_.back() || top_ < blocks_.data() + reusable_.
+  Block* top_;
+
+  static Block g_empty_block;
+};
+
+// Copies of ArenaAllocator use the same thread-compatible Arena without synchronization.
+template <class T>
+class ArenaAllocator {
+ public:
+  using value_type = T;
+  using pointer = T*;
+  using const_pointer = const T*;
+  using reference = T&;
+  using const_reference = const T&;
+  using size_type = size_t;
+  using difference_type = ptrdiff_t;
+  using propagate_on_container_move_assignment = std::true_type;
+  template <class U>
+  struct rebind {
+    using other = ArenaAllocator<U>;
+  };
+  using is_always_equal = std::false_type;
+
+  ArenaAllocator(Arena* arena = nullptr) : arena_(*arena) {}
+
+  Arena& arena() const { return arena_; }
+
+  pointer address(reference x) const { return &x; }
+  const_pointer address(const_reference x) const { return &x; }
+  pointer allocate(size_type n, const void* hint = nullptr) { return arena_.Allocate<T>(n); }
+  void deallocate(T* p, std::size_t n) {}
+  size_type max_size() const { return std::numeric_limits<size_type>::max() / sizeof(value_type); }
+
+  template <class U, class... Args>
+  void construct(U* p, Args&&... args) {
+    ::new (const_cast<void*>(static_cast<const void*>(p))) U(std::forward<Args>(args)...);
+  }
+
+  template <class U>
+  void destroy(U* p) {
+    p->~U();
+  }
+
+  bool operator==(const ArenaAllocator& other) const { return &arena_ == &other.arena_; }
+  bool operator!=(const ArenaAllocator& other) const { return &arena_ != &other.arena_; }
+
+ private:
+  Arena& arena_;
+};
+
+template <class C>
+struct LazyWithArena;
+
+template <template <class, class> class C, class T1, class A>
+struct LazyWithArena<C<T1, A>> {
+  using type = C<T1, ArenaAllocator<typename C<T1, A>::value_type>>;
+};
+
+template <template <class, class, class> class C, class T1, class T2, class A>
+struct LazyWithArena<C<T1, T2, A>> {
+  using type = C<T1, T2, ArenaAllocator<typename C<T1, T2, A>::value_type>>;
+};
+
+template <class C>
+using WithArena = typename LazyWithArena<C>::type;
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_DIR_H_
diff --git a/src/bits.h b/src/bits.h
new file mode 100644
index 00000000..c1a7dcb6
--- /dev/null
+++ b/src/bits.h
@@ -0,0 +1,29 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_BITS_H_
+#define ROMKATV_GITSTATUS_BITS_H_
+
+#include <cstddef>
+
+namespace gitstatus {
+
+inline size_t NextPow2(size_t n) { return n < 2 ? 1 : (~size_t{0} >> __builtin_clzll(n - 1)) + 1; }
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_BITS_H_
diff --git a/src/check.h b/src/check.h
new file mode 100644
index 00000000..82dceae1
--- /dev/null
+++ b/src/check.h
@@ -0,0 +1,61 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_CHECK_H_
+#define ROMKATV_GITSTATUS_CHECK_H_
+
+#include "logging.h"
+
+#include <stdexcept>
+
+// The argument must be an expression convertible to bool.
+// Does nothing if the expression evalutes to true. Otherwise
+// it's equivalent to LOG(FATAL).
+#define CHECK(cond...) \
+  static_cast<void>(0), (!!(cond)) ? static_cast<void>(0) : LOG(FATAL) << #cond << ": "
+
+#define VERIFY(cond...)                                               \
+  static_cast<void>(0), ::gitstatus::internal_check::Thrower(!(cond)) \
+                            ? static_cast<void>(0)                    \
+                            : LOG(ERROR) << #cond << ": "
+
+namespace gitstatus {
+
+struct Exception : std::exception {
+  const char* what() const noexcept override { return "Exception"; }
+};
+
+namespace internal_check {
+
+class Thrower {
+ public:
+  Thrower(bool should_throw) : throw_(should_throw) {}
+  Thrower(Thrower&&) = delete;
+  explicit operator bool() const { return !throw_; }
+  ~Thrower() noexcept(false) {
+    if (throw_) throw Exception();
+  }
+
+ private:
+  bool throw_;
+};
+
+}  // namespace internal_check
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_CHECK_H_
diff --git a/src/check_dir_mtime.cc b/src/check_dir_mtime.cc
new file mode 100644
index 00000000..bb60ffe5
--- /dev/null
+++ b/src/check_dir_mtime.cc
@@ -0,0 +1,157 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "check_dir_mtime.h"
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <time.h>
+#include <unistd.h>
+
+#include <cerrno>
+#include <cstring>
+#include <ctime>
+#include <string>
+#include <vector>
+
+#include "check.h"
+#include "dir.h"
+#include "logging.h"
+#include "print.h"
+#include "scope_guard.h"
+#include "stat.h"
+
+namespace gitstatus {
+
+namespace {
+
+constexpr char kDirPrefix[] = ".gitstatus.";
+
+void Touch(const char* path) {
+  int fd = creat(path, 0444);
+  VERIFY(fd >= 0) << Errno();
+  CHECK(!close(fd)) << Errno();
+}
+
+bool StatChanged(const char* path, const struct stat& prev) {
+  struct stat cur;
+  VERIFY(!lstat(path, &cur)) << Errno();
+  return !StatEq(prev, cur);
+}
+
+void RemoveStaleDirs(const char* root_dir) {
+  int dir_fd = open(root_dir, O_DIRECTORY | O_CLOEXEC);
+  if (dir_fd < 0) return;
+  ON_SCOPE_EXIT(&) { CHECK(!close(dir_fd)) << Errno(); };
+
+  Arena arena;
+  std::vector<char*> entries;
+  const std::time_t now = std::time(nullptr);
+  if (!ListDir(dir_fd, arena, entries,
+               /* precompose_unicode = */ false,
+               /* case_sensitive = */ true)) {
+    return;
+  }
+
+  std::string path = root_dir;
+  const size_t root_dir_len = path.size();
+
+  for (const char* entry : entries) {
+    if (std::strlen(entry) < std::strlen(kDirPrefix)) continue;
+    if (std::memcmp(entry, kDirPrefix, std::strlen(kDirPrefix))) continue;
+
+    struct stat st;
+    if (fstatat(dir_fd, entry, &st, AT_SYMLINK_NOFOLLOW)) {
+      LOG(WARN) << "Cannot stat " << Print(entry) << " in " << Print(root_dir) << ": " << Errno();
+      continue;
+    }
+    if (MTim(st).tv_sec + 10 > now) continue;
+
+    path.resize(root_dir_len);
+    path += entry;
+    size_t dir_len = path.size();
+
+    path += "/b/1";
+    if (unlink(path.c_str()) && errno != ENOENT) {
+      LOG(WARN) << "Cannot unlink " << Print(path) << ": " << Errno();
+      continue;
+    }
+
+    for (const char* d : {"/a/1", "/a", "/b", ""}) {
+      path.resize(dir_len);
+      path += d;
+      if (rmdir(path.c_str()) && errno != ENOENT) {
+        LOG(WARN) << "Cannot remove " << Print(path) << ": " << Errno();
+        break;
+      }
+    }
+  }
+}
+
+}  // namespace
+
+bool CheckDirMtime(const char* root_dir) {
+  try {
+    RemoveStaleDirs(root_dir);
+
+    std::string tmp = std::string() + root_dir + kDirPrefix + "XXXXXX";
+    VERIFY(mkdtemp(&tmp[0])) << Errno();
+    ON_SCOPE_EXIT(&) { rmdir(tmp.c_str()); };
+
+    std::string a_dir = tmp + "/a";
+    VERIFY(!mkdir(a_dir.c_str(), 0755)) << Errno();
+    ON_SCOPE_EXIT(&) { rmdir(a_dir.c_str()); };
+    struct stat a_st;
+    VERIFY(!lstat(a_dir.c_str(), &a_st)) << Errno();
+
+    std::string b_dir = tmp + "/b";
+    VERIFY(!mkdir(b_dir.c_str(), 0755)) << Errno();
+    ON_SCOPE_EXIT(&) { rmdir(b_dir.c_str()); };
+    struct stat b_st;
+    VERIFY(!lstat(b_dir.c_str(), &b_st)) << Errno();
+
+    while (sleep(1)) {
+      // zzzz
+    }
+
+    std::string a1 = a_dir + "/1";
+    VERIFY(!mkdir(a1.c_str(), 0755)) << Errno();
+    ON_SCOPE_EXIT(&) { rmdir(a1.c_str()); };
+    if (!StatChanged(a_dir.c_str(), a_st)) {
+      LOG(WARN) << "Creating a directory doesn't change mtime of the parent: " << Print(root_dir);
+      return false;
+    }
+
+    std::string b1 = b_dir + "/1";
+    Touch(b1.c_str());
+    ON_SCOPE_EXIT(&) { unlink(b1.c_str()); };
+    if (!StatChanged(b_dir.c_str(), b_st)) {
+      LOG(WARN) << "Creating a file doesn't change mtime of the parent: " << Print(root_dir);
+      return false;
+    }
+
+    LOG(INFO) << "All mtime checks have passes. Enabling untracked cache: " << Print(root_dir);
+    return true;
+  } catch (const Exception&) {
+    LOG(WARN) << "Error while testing for mtime capability: " << Print(root_dir);
+    return false;
+  }
+}
+
+}  // namespace gitstatus
diff --git a/src/check_dir_mtime.h b/src/check_dir_mtime.h
new file mode 100644
index 00000000..c9204e95
--- /dev/null
+++ b/src/check_dir_mtime.h
@@ -0,0 +1,31 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_CHECK_DIR_MTIME_H_
+#define ROMKATV_GITSTATUS_CHECK_DIR_MTIME_H_
+
+namespace gitstatus {
+
+// Similar to `git update-index --test-untracked-cache` but performs all tests
+// in parallel, so the total testing time is one second regardless of the number
+// of tests. It also performs fewer tests because gitstatus imposes fewer
+// requirements on the filesystem in order to take advantage of untracked cache.
+bool CheckDirMtime(const char* root_dir);
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_CHECK_DIR_MTIME_H_
diff --git a/src/dir.cc b/src/dir.cc
new file mode 100644
index 00000000..14bc6ac4
--- /dev/null
+++ b/src/dir.cc
@@ -0,0 +1,234 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "dir.h"
+
+#include <algorithm>
+#include <atomic>
+#include <cerrno>
+#include <cstring>
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#ifdef __linux__
+#include <endian.h>
+#include <sys/syscall.h>
+#endif
+
+#ifdef __APPLE__
+#include <iconv.h>
+#endif
+
+#include "bits.h"
+#include "check.h"
+#include "scope_guard.h"
+#include "string_cmp.h"
+#include "tribool.h"
+
+namespace gitstatus {
+
+namespace {
+
+bool Dots(const char* name) {
+  if (name[0] == '.') {
+    if (name[1] == 0) return true;
+    if (name[1] == '.' && name[2] == 0) return true;
+  }
+  return false;
+}
+
+}  // namespace
+
+// The linux-specific implementation is about 20% faster than the generic (posix) implementation.
+#ifdef __linux__
+
+uint64_t Read64(const void* p) {
+  uint64_t res;
+  std::memcpy(&res, p, 8);
+  return res;
+}
+
+void Write64(uint64_t x, void* p) { std::memcpy(p, &x, 8); }
+
+void SwapBytes(char** begin, char** end) {
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+  for (; begin != end; ++begin) Write64(__builtin_bswap64(Read64(*begin)), *begin);
+#elif __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__
+#error "sorry, not implemented"
+#endif
+}
+
+template <bool kCaseSensitive>
+void SortEntries(char** begin, char** end) {
+  static_assert(kCaseSensitive, "");
+  SwapBytes(begin, end);
+  std::sort(begin, end, [](const char* a, const char* b) {
+    uint64_t x = Read64(a);
+    uint64_t y = Read64(b);
+    // Add 5 for good luck.
+    return x < y || (x == y && std::memcmp(a + 5, b + 5, 256) < 0);
+  });
+  SwapBytes(begin, end);
+}
+
+template <>
+void SortEntries<false>(char** begin, char** end) {
+  std::sort(begin, end, StrLt<false>());
+}
+
+bool ListDir(int dir_fd, Arena& arena, std::vector<char*>& entries, bool precompose_unicode,
+             bool case_sensitive) {
+  struct linux_dirent64 {
+    ino64_t d_ino;
+    off64_t d_off;
+    unsigned short d_reclen;
+    unsigned char d_type;
+    char d_name[];
+  };
+
+  constexpr size_t kBufSize = 8 << 10;
+  entries.clear();
+
+  while (true) {
+    char* buf = static_cast<char*>(arena.Allocate(kBufSize, alignof(linux_dirent64)));
+    // Save 256 bytes for the rainy day.
+    int n = syscall(SYS_getdents64, dir_fd, buf, kBufSize - 256);
+    if (n < 0) {
+      entries.clear();
+      return false;
+    }
+    if (n == 0) break;
+    for (int pos = 0; pos < n;) {
+      auto* ent = reinterpret_cast<linux_dirent64*>(buf + pos);
+      if (!Dots(ent->d_name)) entries.push_back(ent->d_name);
+      pos += ent->d_reclen;
+      // It's tempting to bail here if n + sizeof(linux_dirent64) + 512 <= n. After all, there
+      // was enough space for another entry but SYS_getdents64 didn't write it, so this must be
+      // the end of the directory listing, right? Unfortuatenly, no. SYS_getdents64 is finicky.
+      // It sometimes writes a partial list of entries even if the full list would fit.
+    }
+  }
+
+  if (case_sensitive) {
+    SortEntries<true>(entries.data(), entries.data() + entries.size());
+  } else {
+    SortEntries<false>(entries.data(), entries.data() + entries.size());
+  }
+
+  return true;
+}
+
+#else  // __linux__
+
+namespace {
+
+char* DirentDup(Arena& arena, const struct dirent& ent, size_t len) {
+  char* p = arena.Allocate<char>(len + 2);
+  *p++ = ent.d_type;
+  std::memcpy(p, ent.d_name, len + 1);
+  return p;
+}
+
+#ifdef __APPLE__
+
+std::atomic<bool> g_iconv_error(true);
+
+Tribool IConvTry(char* inp, size_t ins, char* outp, size_t outs) {
+  if (outs == 0) return Tribool::kUnknown;
+  iconv_t ic = iconv_open("UTF-8", "UTF-8-MAC");
+  if (ic == (iconv_t)-1) {
+    if (g_iconv_error.load(std::memory_order_relaxed) &&
+        g_iconv_error.exchange(false, std::memory_order_relaxed)) {
+      LOG(ERROR) << "iconv_open(\"UTF-8\", \"UTF-8-MAC\") failed";
+    }
+    return Tribool::kFalse;
+  }
+  ON_SCOPE_EXIT(&) { CHECK(iconv_close(ic) == 0) << Errno(); };
+  --outs;
+  if (iconv(ic, &inp, &ins, &outp, &outs) >= 0) {
+    *outp = 0;
+    return Tribool::kTrue;
+  }
+  return errno == E2BIG ? Tribool::kUnknown : Tribool::kFalse;
+}
+
+char* DirenvConvert(Arena& arena, struct dirent& ent, bool do_convert) {
+  if (!do_convert) return DirentDup(arena, ent, std::strlen(ent.d_name));
+
+  size_t len = 0;
+  do_convert = false;
+  for (unsigned char c; (c = ent.d_name[len]); ++len) {
+    if (c & 0x80) do_convert = true;
+  }
+  if (!do_convert) return DirentDup(arena, ent, len);
+
+  size_t n = NextPow2(len + 2);
+  while (true) {
+    char* p = arena.Allocate<char>(n);
+    switch (IConvTry(ent.d_name, len, p + 1, n - 1)) {
+      case Tribool::kFalse:
+        return DirentDup(arena, ent, len);
+      case Tribool::kTrue:
+        *p = ent.d_type;
+        return p + 1;
+      case Tribool::kUnknown:
+        break;
+    }
+    n *= 2;
+  }
+}
+
+#else  // __APPLE__
+
+char* DirenvConvert(Arena& arena, struct dirent& ent, bool do_convert) {
+  return DirentDup(arena, ent, std::strlen(ent.d_name));
+}
+
+#endif  // __APPLE__
+
+}  // namespace
+
+bool ListDir(int dir_fd, Arena& arena, std::vector<char*>& entries, bool precompose_unicode,
+             bool case_sensitive) {
+  VERIFY((dir_fd = dup(dir_fd)) >= 0);
+  DIR* dir = fdopendir(dir_fd);
+  if (!dir) {
+    CHECK(!close(dir_fd)) << Errno();
+    return -1;
+  }
+  ON_SCOPE_EXIT(&) { CHECK(!closedir(dir)) << Errno(); };
+  entries.clear();
+  while (struct dirent* ent = (errno = 0, readdir(dir))) {
+    if (Dots(ent->d_name)) continue;
+    entries.push_back(DirenvConvert(arena, *ent, precompose_unicode));
+  }
+  if (errno) {
+    entries.clear();
+    return false;
+  }
+  StrSort(entries.data(), entries.data() + entries.size(), case_sensitive);
+  return true;
+}
+
+#endif  // __linux__
+
+}  // namespace gitstatus
diff --git a/src/dir.h b/src/dir.h
new file mode 100644
index 00000000..42ab29bb
--- /dev/null
+++ b/src/dir.h
@@ -0,0 +1,50 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_DIR_H_
+#define ROMKATV_GITSTATUS_DIR_H_
+
+#include <cstddef>
+#include <vector>
+
+#include "arena.h"
+
+namespace gitstatus {
+
+// On error, clears entries and returns false. Does not throw.
+//
+// On success, fills entries with the names of files from the specified directory and returns true.
+// Every entry is a null-terminated string. At -1 offset is its d_type. All elements point into the
+// arena. They are sorted either by strcmp or strcasecmp depending on case_sensitive.
+//
+// Does not close dir_fd.
+//
+// There are two distinct implementations of ListDir -- one for Linux and another for everything
+// else. The linux-specific implementation is 20% faster.
+//
+// The reason sorting is bundled with directory listing is performance on Linux. The API of
+// getdents64 allows for much faster sorting than what can be done with a plain vector<char*>.
+// For the POSIX implementation there is no need to bundle sorting in this way. In fact, it's
+// done at the end with a generic StrSort() call.
+//
+// For best results, reuse the arena and vector for multiple calls to avoid heap allocations.
+bool ListDir(int dir_fd, Arena& arena, std::vector<char*>& entries, bool precompose_unicode,
+             bool case_sensitive);
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_DIR_H_
diff --git a/src/git.cc b/src/git.cc
new file mode 100644
index 00000000..029b02bf
--- /dev/null
+++ b/src/git.cc
@@ -0,0 +1,242 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "git.h"
+
+#include <cstdlib>
+#include <cstring>
+#include <fstream>
+#include <sstream>
+#include <utility>
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "arena.h"
+#include "check.h"
+#include "print.h"
+#include "scope_guard.h"
+
+namespace gitstatus {
+
+const char* GitError() {
+  const git_error* err = git_error_last();
+  return err && err->message ? err->message : "unknown error";
+}
+
+std::string RepoState(git_repository* repo) {
+  Arena arena;
+  StringView gitdir(git_repository_path(repo));
+
+  // These names mostly match gitaction in vcs_info:
+  // https://github.com/zsh-users/zsh/blob/master/Functions/VCS_Info/Backends/VCS_INFO_get_data_git.
+  auto State = [&]() {
+    switch (git_repository_state(repo)) {
+      case GIT_REPOSITORY_STATE_NONE:
+        return "";
+      case GIT_REPOSITORY_STATE_MERGE:
+        return "merge";
+      case GIT_REPOSITORY_STATE_REVERT:
+        return "revert";
+      case GIT_REPOSITORY_STATE_REVERT_SEQUENCE:
+        return "revert-seq";
+      case GIT_REPOSITORY_STATE_CHERRYPICK:
+        return "cherry";
+      case GIT_REPOSITORY_STATE_CHERRYPICK_SEQUENCE:
+        return "cherry-seq";
+      case GIT_REPOSITORY_STATE_BISECT:
+        return "bisect";
+      case GIT_REPOSITORY_STATE_REBASE:
+        return "rebase";
+      case GIT_REPOSITORY_STATE_REBASE_INTERACTIVE:
+        return "rebase-i";
+      case GIT_REPOSITORY_STATE_REBASE_MERGE:
+        return "rebase-m";
+      case GIT_REPOSITORY_STATE_APPLY_MAILBOX:
+        return "am";
+      case GIT_REPOSITORY_STATE_APPLY_MAILBOX_OR_REBASE:
+        return "am/rebase";
+    }
+    return "action";
+  };
+
+  auto DirExists = [&](StringView name) {
+    int fd = open(arena.StrCat(gitdir, "/", name), O_DIRECTORY | O_CLOEXEC);
+    if (fd < 0) return false;
+    CHECK(!close(fd)) << Errno();
+    return true;
+  };
+
+  auto ReadFile = [&](StringView name) {
+    std::ifstream strm(arena.StrCat(gitdir, "/", name));
+    std::string res;
+    strm >> res;
+    return res;
+  };
+
+  std::string next;
+  std::string last;
+
+  if (DirExists("rebase-merge")) {
+    next = ReadFile("rebase-merge/msgnum");
+    last = ReadFile("rebase-merge/end");
+  } else if (DirExists("rebase-apply")) {
+    next = ReadFile("rebase-apply/next");
+    last = ReadFile("rebase-apply/last");
+  }
+
+  std::ostringstream res;
+  res << State();
+  if (!next.empty() && !last.empty()) res << ' ' << next << '/' << last;
+  return res.str();
+}
+
+size_t CountRange(git_repository* repo, const std::string& range) {
+  git_revwalk* walk = nullptr;
+  VERIFY(!git_revwalk_new(&walk, repo)) << GitError();
+  ON_SCOPE_EXIT(=) { git_revwalk_free(walk); };
+  VERIFY(!git_revwalk_push_range(walk, range.c_str())) << GitError();
+  size_t res = 0;
+  while (true) {
+    git_oid oid;
+    switch (git_revwalk_next(&oid, walk)) {
+      case 0:
+        ++res;
+        break;
+      case GIT_ITEROVER:
+        return res;
+      default:
+        LOG(ERROR) << "git_revwalk_next: " << range << ": " << GitError();
+        throw Exception();
+    }
+  }
+}
+
+size_t NumStashes(git_repository* repo) {
+  size_t res = 0;
+  auto* cb = +[](size_t index, const char* message, const git_oid* stash_id, void* payload) {
+    ++*static_cast<size_t*>(payload);
+    return 0;
+  };
+  if (!git_stash_foreach(repo, cb, &res)) return res;
+  // Example error: failed to parse signature - malformed e-mail.
+  // See https://github.com/romkatv/powerlevel10k/issues/216.
+  LOG(WARN) << "git_stash_foreach: " << GitError();
+  return 0;
+}
+
+git_reference* Head(git_repository* repo) {
+  git_reference* symbolic = nullptr;
+  switch (git_reference_lookup(&symbolic, repo, "HEAD")) {
+    case 0:
+      break;
+    case GIT_ENOTFOUND:
+      return nullptr;
+    default:
+      LOG(ERROR) << "git_reference_lookup: " << GitError();
+      throw Exception();
+  }
+
+  git_reference* direct = nullptr;
+  if (git_reference_resolve(&direct, symbolic)) {
+    LOG(INFO) << "Empty git repo (no HEAD)";
+    return symbolic;
+  }
+  git_reference_free(symbolic);
+  return direct;
+}
+
+const char* LocalBranchName(const git_reference* ref) {
+  CHECK(ref);
+  git_reference_t type = git_reference_type(ref);
+  switch (type) {
+    case GIT_REFERENCE_DIRECT: {
+      return git_reference_is_branch(ref) ? git_reference_shorthand(ref) : "";
+    }
+    case GIT_REFERENCE_SYMBOLIC: {
+      static constexpr char kHeadPrefix[] = "refs/heads/";
+      const char* target = git_reference_symbolic_target(ref);
+      if (!target) return "";
+      size_t len = std::strlen(target);
+      if (len < sizeof(kHeadPrefix)) return "";
+      if (std::memcmp(target, kHeadPrefix, sizeof(kHeadPrefix) - 1)) return "";
+      return target + (sizeof(kHeadPrefix) - 1);
+    }
+    case GIT_REFERENCE_INVALID:
+    case GIT_REFERENCE_ALL:
+      break;
+  }
+  LOG(ERROR) << "Invalid reference type: " << type;
+  throw Exception();
+}
+
+RemotePtr GetRemote(git_repository* repo, const git_reference* local) {
+  git_remote* remote;
+  git_buf symref = {};
+  if (git_branch_remote(&remote, &symref, repo, git_reference_name(local))) return nullptr;
+  ON_SCOPE_EXIT(&) {
+    git_remote_free(remote);
+    git_buf_free(&symref);
+  };
+
+  git_reference* ref;
+  if (git_reference_lookup(&ref, repo, symref.ptr)) return nullptr;
+  ON_SCOPE_EXIT(&) { if (ref) git_reference_free(ref); };
+
+  const char* branch = nullptr;
+  std::string name = remote ? git_remote_name(remote) : ".";
+  if (git_branch_name(&branch, ref)) {
+    branch = "";
+  } else if (remote) {
+    VERIFY(std::strstr(branch, name.c_str()) == branch);
+    VERIFY(branch[name.size()] == '/');
+    branch += name.size() + 1;
+  }
+
+  auto res = std::make_unique<Remote>();
+  res->name = std::move(name);
+  res->branch = branch;
+  res->url = remote ? (git_remote_url(remote) ?: "") : "";
+  res->ref = std::exchange(ref, nullptr);
+  return RemotePtr(res.release());
+}
+
+PushRemotePtr GetPushRemote(git_repository* repo, const git_reference* local) {
+  git_remote* remote;
+  git_buf symref = {};
+  if (git_branch_push_remote(&remote, &symref, repo, git_reference_name(local))) return nullptr;
+  ON_SCOPE_EXIT(&) {
+    git_remote_free(remote);
+    git_buf_free(&symref);
+  };
+
+  git_reference* ref;
+  if (git_reference_lookup(&ref, repo, symref.ptr)) return nullptr;
+  ON_SCOPE_EXIT(&) { if (ref) git_reference_free(ref); };
+
+  std::string name = remote ? git_remote_name(remote) : ".";
+
+  auto res = std::make_unique<PushRemote>();
+  res->name = std::move(name);
+  res->url = remote ? (git_remote_url(remote) ?: "") : "";
+  res->ref = std::exchange(ref, nullptr);
+  return PushRemotePtr(res.release());
+}
+
+}  // namespace gitstatus
diff --git a/src/git.h b/src/git.h
new file mode 100644
index 00000000..7e5a6f9d
--- /dev/null
+++ b/src/git.h
@@ -0,0 +1,106 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_GIT_H_
+#define ROMKATV_GITSTATUS_GIT_H_
+
+#include <git2.h>
+
+#include <cstddef>
+#include <memory>
+#include <string>
+
+namespace gitstatus {
+
+// Not null.
+const char* GitError();
+
+// Not null.
+std::string RepoState(git_repository* repo);
+
+// Returns the number of commits in the range.
+size_t CountRange(git_repository* repo, const std::string& range);
+
+// How many stashes are there?
+size_t NumStashes(git_repository* repo);
+
+// Returns the origin URL or an empty string. Not null.
+std::string RemoteUrl(git_repository* repo, const git_reference* ref);
+
+// Returns reference to HEAD or null if not found. The reference is symbolic if the repo is empty
+// and direct otherwise.
+git_reference* Head(git_repository* repo);
+
+// Returns the name of the local branch, or an empty string.
+const char* LocalBranchName(const git_reference* ref);
+
+struct Remote {
+  // Tip of the remote branch.
+  git_reference* ref;
+
+  // Name of the tracking remote. For example, "origin".
+  std::string name;
+
+  // Name of the tracking remote branch. For example, "master".
+  std::string branch;
+
+  // URL of the tracking remote. For example, "https://foo.com/repo.git".
+  std::string url;
+
+  // Note: pushurl is not exposed (but could be).
+
+  struct Free {
+    void operator()(const Remote* p) const {
+      if (p) {
+        if (p->ref) git_reference_free(p->ref);
+        delete p;
+      }
+    }
+  };
+};
+
+struct PushRemote {
+  // Tip of the remote branch.
+  git_reference* ref;
+
+  // Name of the tracking remote. For example, "origin".
+  std::string name;
+
+  // URL of the tracking remote. For example, "https://foo.com/repo.git".
+  std::string url;
+
+  // Note: pushurl is not exposed (but could be).
+
+  struct Free {
+    void operator()(const PushRemote* p) const {
+      if (p) {
+        if (p->ref) git_reference_free(p->ref);
+        delete p;
+      }
+    }
+  };
+};
+
+using RemotePtr = std::unique_ptr<Remote, Remote::Free>;
+using PushRemotePtr = std::unique_ptr<PushRemote, PushRemote::Free>;
+
+RemotePtr GetRemote(git_repository* repo, const git_reference* local);
+PushRemotePtr GetPushRemote(git_repository* repo, const git_reference* local);
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_GIT_H_
diff --git a/src/gitstatus.cc b/src/gitstatus.cc
new file mode 100644
index 00000000..35351b85
--- /dev/null
+++ b/src/gitstatus.cc
@@ -0,0 +1,210 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include <time.h>
+
+#include <cstddef>
+#include <future>
+#include <string>
+
+#include <git2.h>
+
+#include "check.h"
+#include "git.h"
+#include "logging.h"
+#include "options.h"
+#include "print.h"
+#include "repo.h"
+#include "repo_cache.h"
+#include "request.h"
+#include "response.h"
+#include "scope_guard.h"
+#include "thread_pool.h"
+#include "timer.h"
+
+namespace gitstatus {
+namespace {
+
+using namespace std::string_literals;
+
+void ProcessRequest(const Options& opts, RepoCache& cache, Request req) {
+  Timer timer;
+  ON_SCOPE_EXIT(&) { timer.Report("request"); };
+
+  ResponseWriter resp(req.id);
+  Repo* repo = cache.Open(req.dir, req.from_dotgit);
+  if (!repo) return;
+
+  git_config* cfg;
+  VERIFY(!git_repository_config(&cfg, repo->repo())) << GitError();
+  ON_SCOPE_EXIT(=) { git_config_free(cfg); };
+  VERIFY(!git_config_refresh(cfg)) << GitError();
+
+  // Symbolic reference if and only if the repo is empty.
+  git_reference* head = Head(repo->repo());
+  if (!head) return;
+  ON_SCOPE_EXIT(=) { git_reference_free(head); };
+
+  // Null if and only if the repo is empty.
+  const git_oid* head_target = git_reference_target(head);
+
+  // Looking up tags may take some time. Do it in the background while we check for stuff.
+  // Note that GetTagName() doesn't access index, so it'll overlap with index reading and
+  // parsing.
+  std::future<std::string> tag = repo->GetTagName(head_target);
+  ON_SCOPE_EXIT(&) {
+    if (tag.valid()) {
+      try {
+        tag.wait();
+      } catch (const Exception&) {
+      }
+    }
+  };
+
+  // Repository working directory. Absolute; no trailing slash. E.g., "/home/romka/gitstatus".
+  StringView workdir(git_repository_workdir(repo->repo()));
+  if (workdir.len == 0) return;
+  if (workdir.len > 1 && workdir.ptr[workdir.len - 1] == '/') --workdir.len;
+  resp.Print(workdir);
+
+  // Revision. Either 40 hex digits or an empty string for empty repo.
+  resp.Print(head_target ? git_oid_tostr_s(head_target) : "");
+
+  // Local branch name (e.g., "master") or empty string if not on a branch.
+  resp.Print(LocalBranchName(head));
+
+  // Remote tracking branch or null.
+  RemotePtr remote = GetRemote(repo->repo(), head);
+
+  // Tracking remote branch name (e.g., "master") or empty string if there is no tracking remote.
+  resp.Print(remote ? remote->branch : "");
+
+  // Tracking remote name (e.g., "origin") or empty string if there is no tracking remote.
+  resp.Print(remote ? remote->name : "");
+
+  // Tracking remote URL or empty string if there is no tracking remote.
+  resp.Print(remote ? remote->url : "");
+
+  // Repository state, A.K.A. action. For example, "merge".
+  resp.Print(RepoState(repo->repo()));
+
+  IndexStats stats;
+  // Look for staged, unstaged and untracked. This is where most of the time is spent.
+  if (req.diff) stats = repo->GetIndexStats(head_target, cfg);
+
+  // The number of files in the index.
+  resp.Print(stats.index_size);
+  // The number of staged changes. At most opts.max_num_staged.
+  resp.Print(stats.num_staged);
+  // The number of unstaged changes. At most opts.max_num_unstaged. 0 if index is too large.
+  resp.Print(stats.num_unstaged);
+  // The number of conflicted changes. At most opts.max_num_conflicted. 0 if index is too large.
+  resp.Print(stats.num_conflicted);
+  // The number of untracked changes. At most opts.max_num_untracked. 0 if index is too large.
+  resp.Print(stats.num_untracked);
+
+  if (remote && remote->ref) {
+    const char* ref = git_reference_shorthand(remote->ref);
+    // Number of commits we are ahead of upstream. Non-negative integer.
+    resp.Print(CountRange(repo->repo(), ref + "..HEAD"s));
+    // Number of commits we are behind upstream. Non-negative integer.
+    resp.Print(CountRange(repo->repo(), "HEAD.."s + ref));
+  } else {
+    resp.Print("0");
+    resp.Print("0");
+  }
+
+  // Number of stashes. Non-negative integer.
+  resp.Print(NumStashes(repo->repo()));
+
+  // Tag that points to HEAD (e.g., "v4.2") or empty string if there aren't any. The same as
+  // `git describe --tags --exact-match`.
+  resp.Print(tag.get());
+
+  // The number of unstaged deleted files. At most stats.num_unstaged.
+  resp.Print(stats.num_unstaged_deleted);
+  // The number of staged new files. At most stats.num_staged.
+  resp.Print(stats.num_staged_new);
+  // The number of staged deleted files. At most stats.num_staged.
+  resp.Print(stats.num_staged_deleted);
+
+  // Push remote or null.
+  PushRemotePtr push_remote = GetPushRemote(repo->repo(), head);
+
+  // Push remote name (e.g., "origin") or empty string if there is no push remote.
+  resp.Print(push_remote ? push_remote->name : "");
+
+  // Push remote URL or empty string if there is no push remote.
+  resp.Print(push_remote ? push_remote->url : "");
+
+  if (push_remote && push_remote->ref) {
+    const char* ref = git_reference_shorthand(push_remote->ref);
+    // Number of commits we are ahead of push remote. Non-negative integer.
+    resp.Print(CountRange(repo->repo(), ref + "..HEAD"s));
+    // Number of commits we are behind upstream. Non-negative integer.
+    resp.Print(CountRange(repo->repo(), "HEAD.."s + ref));
+  } else {
+    resp.Print("0");
+    resp.Print("0");
+  }
+
+  // The number of files in the index with skip-worktree bit set.
+  resp.Print(stats.num_skip_worktree);
+  // The number of files in the index with assume-unchanged bit set.
+  resp.Print(stats.num_assume_unchanged);
+
+  resp.Dump("with git status");
+}
+
+int GitStatus(int argc, char** argv) {
+  tzset();
+  Options opts = ParseOptions(argc, argv);
+  g_min_log_level = opts.log_level;
+  for (int i = 0; i != argc; ++i) LOG(INFO) << "argv[" << i << "]: " << Print(argv[i]);
+  RequestReader reader(fileno(stdin), opts.lock_fd, opts.parent_pid);
+  RepoCache cache(opts);
+
+  InitGlobalThreadPool(opts.num_threads);
+  git_libgit2_opts(GIT_OPT_ENABLE_STRICT_HASH_VERIFICATION, 0);
+  git_libgit2_opts(GIT_OPT_DISABLE_INDEX_CHECKSUM_VERIFICATION, 1);
+  git_libgit2_opts(GIT_OPT_DISABLE_INDEX_FILEPATH_VALIDATION, 1);
+  git_libgit2_opts(GIT_OPT_DISABLE_READNG_PACKED_TAGS, 1);
+  git_libgit2_init();
+
+  while (true) {
+    try {
+      Request req;
+      if (reader.ReadRequest(req)) {
+        LOG(INFO) << "Processing request: " << req;
+        try {
+          ProcessRequest(opts, cache, req);
+          LOG(INFO) << "Successfully processed request: " << req;
+        } catch (const Exception&) {
+          LOG(ERROR) << "Error processing request: " << req;
+        }
+      } else if (opts.repo_ttl >= Duration()) {
+        cache.Free(Clock::now() - opts.repo_ttl);
+      }
+    } catch (const Exception&) {
+    }
+  }
+}
+
+}  // namespace
+}  // namespace gitstatus
+
+int main(int argc, char** argv) { gitstatus::GitStatus(argc, argv); }
diff --git a/src/index.cc b/src/index.cc
new file mode 100644
index 00000000..ae8ca54c
--- /dev/null
+++ b/src/index.cc
@@ -0,0 +1,455 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "index.h"
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <condition_variable>
+#include <cstdint>
+#include <cstring>
+#include <iomanip>
+#include <iterator>
+#include <mutex>
+#include <stack>
+
+#include "algorithm.h"
+#include "check.h"
+#include "dir.h"
+#include "git.h"
+#include "index.h"
+#include "print.h"
+#include "scope_guard.h"
+#include "stat.h"
+#include "string_cmp.h"
+#include "thread_pool.h"
+
+namespace gitstatus {
+
+namespace {
+
+void CommonDir(Str<> str, const char* a, const char* b, size_t* dir_len, size_t* dir_depth) {
+  *dir_len = 0;
+  *dir_depth = 0;
+  for (size_t i = 1; str.Eq(*a, *b) && *a; ++i, ++a, ++b) {
+    if (*a == '/') {
+      *dir_len = i;
+      ++*dir_depth;
+    }
+  }
+}
+
+size_t Weight(const IndexDir& dir) { return 1 + dir.subdirs.size() + dir.files.size(); }
+
+bool MTimeEq(const git_index_time& index, const struct timespec& workdir) {
+  if (index.seconds != workdir.tv_sec) return false;
+  if (int64_t{index.nanoseconds} == workdir.tv_nsec) return true;
+#ifdef GITSTATUS_ZERO_NSEC
+  return index.nanoseconds == 0;
+#else
+  return false;
+#endif
+}
+
+bool IsModified(const git_index_entry* entry, const struct stat& st, const RepoCaps& caps) {
+  mode_t mode = st.st_mode;
+  if (S_ISREG(mode)) {
+    if (!caps.has_symlinks && S_ISLNK(entry->mode)) {
+      mode = entry->mode;
+    } else if (!caps.trust_filemode) {
+      mode = entry->mode;
+    } else {
+      mode = S_IFREG | (mode & 0100 ? 0755 : 0644);
+    }
+  } else {
+    mode &= S_IFMT;
+  }
+
+  bool res = false;
+
+#define COND(field, cond...) \
+  if (cond) {                \
+  } else                     \
+    res = true,              \
+    LOG(DEBUG) << "Dirty candidate (modified): " << Print(entry->path) << ": " #field " "
+
+  COND(ino, !entry->ino || entry->ino == static_cast<std::uint32_t>(st.st_ino))
+      << entry->ino << " => " << static_cast<std::uint32_t>(st.st_ino);
+
+  COND(stage, GIT_INDEX_ENTRY_STAGE(entry) == 0) << "=> " << GIT_INDEX_ENTRY_STAGE(entry);
+  COND(fsize, int64_t{entry->file_size} == st.st_size) << entry->file_size << " => " << st.st_size;
+  COND(mtime, MTimeEq(entry->mtime, MTim(st))) << Print(entry->mtime) << " => " << Print(MTim(st));
+  COND(mode, entry->mode == mode) << std::oct << entry->mode << " => " << std::oct << mode;
+
+#undef COND
+
+  return res;
+}
+
+int OpenDir(int parent_fd, const char* name) {
+  return openat(parent_fd, name, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+}
+
+void OpenTail(int* fds, size_t nfds, int root_fd, StringView dirname, Arena& arena) {
+  CHECK(fds && nfds && root_fd >= 0);
+  std::fill(fds, fds + nfds, -1);
+  if (!dirname.len) return;
+  CHECK(dirname.len > 1);
+  CHECK(dirname.ptr[0] != '/');
+  CHECK(dirname.ptr[dirname.len - 1] == '/');
+
+  char* begin = arena.StrDup(dirname.ptr, dirname.len - 1);
+  WithArena<std::vector<const char*>> subdirs(&arena);
+  subdirs.reserve(nfds + 1);
+
+  for (char* sep = begin + dirname.len - 1; subdirs.size() < nfds;) {
+    sep = FindLast(begin, sep, '/');
+    if (sep == begin) break;
+    *sep = 0;
+    subdirs.push_back(sep + 1);
+  }
+  subdirs.push_back(begin);
+  if (subdirs.size() < nfds + 1) subdirs.push_back(".");
+  CHECK(subdirs.size() <= nfds + 1);
+
+  for (size_t i = subdirs.size(); i != 1; --i) {
+    const char* path = subdirs[i - 1];
+    if ((root_fd = OpenDir(root_fd, path)) < 0) {
+      for (; i != subdirs.size(); ++i) {
+        CHECK(!close(fds[i - 1])) << Errno();
+        fds[i - 1] = -1;
+      }
+      return;
+    }
+    fds[i - 2] = root_fd;
+  }
+}
+
+std::vector<const char*> ScanDirs(git_index* index, int root_fd, IndexDir* const* begin,
+                                  IndexDir* const* end, const RepoCaps& caps,
+                                  const ScanOpts& opts) {
+  const Str<> str(caps.case_sensitive);
+
+  Arena arena;
+  std::vector<const char*> dirty_candidates;
+  std::vector<char*> entries;
+  entries.reserve(128);
+
+  auto AddCandidate = [&](const char* kind, const char* path) {
+    if (kind) LOG(DEBUG) << "Dirty candidate (" << kind << "): " << Print(path);
+    dirty_candidates.push_back(path);
+  };
+
+  constexpr ssize_t kDirStackSize = 5;
+  int dir_fd[kDirStackSize];
+  std::fill(std::begin(dir_fd), std::end(dir_fd), -1);
+  auto Close = [](int& fd) {
+    if (fd >= 0) {
+      CHECK(!close(fd)) << Errno();
+      fd = -1;
+    }
+  };
+  auto CloseAll = [&] { std::for_each(std::begin(dir_fd), std::end(dir_fd), Close); };
+  ON_SCOPE_EXIT(&) { CloseAll(); };
+  if (begin != end) OpenTail(dir_fd, kDirStackSize, root_fd, (*begin)->path, arena);
+
+  for (IndexDir* const* it = begin; it != end; ++it) {
+    IndexDir& dir = **it;
+
+    auto Basename = [&](const git_index_entry* e) { return e->path + dir.path.len; };
+
+    auto AddUnmached = [&](StringView basename) {
+      if (!basename.len) {
+        dir.st = {};
+        dir.unmatched.clear();
+        dir.arena.Reuse();
+      } else if (str.Eq(basename, StringView(".git/"))) {
+        return;
+      }
+      char* path = dir.arena.StrCat(dir.path, basename);
+      dir.unmatched.push_back(path);
+      AddCandidate(basename.len ? "new" : "unreadable", path);
+    };
+
+    auto StatFiles = [&]() {
+      struct stat st;
+      for (const git_index_entry* file : dir.files) {
+        if (fstatat(*dir_fd, Basename(file), &st, AT_SYMLINK_NOFOLLOW)) {
+          AddCandidate(errno == ENOENT ? "deleted" : "unreadable", file->path);
+        } else if (IsModified(file, st, caps)) {
+          AddCandidate(nullptr, file->path);
+        }
+      }
+    };
+
+    ssize_t d = 0;
+    if ((it == begin || (d = it[-1]->depth + 1 - dir.depth) < kDirStackSize) && dir_fd[d] >= 0) {
+      CHECK(d >= 0);
+      int fd = OpenDir(dir_fd[d], arena.StrDup(dir.basename.ptr, dir.basename.len));
+      for (ssize_t i = 0; i != d; ++i) Close(dir_fd[i]);
+      std::rotate(dir_fd, dir_fd + (d ? d : kDirStackSize) - 1, dir_fd + kDirStackSize);
+      Close(*dir_fd);
+      *dir_fd = fd;
+    } else {
+      CloseAll();
+      if (dir.path.len) {
+        CHECK(dir.path.ptr[0] != '/');
+        CHECK(dir.path.ptr[dir.path.len - 1] == '/');
+        *dir_fd = OpenDir(root_fd, arena.StrDup(dir.path.ptr, dir.path.len - 1));
+      } else {
+        VERIFY((*dir_fd = dup(root_fd)) >= 0) << Errno();
+      }
+    }
+    if (*dir_fd < 0) {
+      CloseAll();
+      AddUnmached("");
+      continue;
+    }
+
+    if (!opts.include_untracked) {
+      StatFiles();
+      continue;
+    }
+
+    if (opts.untracked_cache != Tribool::kFalse) {
+      struct stat st;
+      if (fstat(*dir_fd, &st)) {
+        AddUnmached("");
+        continue;
+      }
+      if (opts.untracked_cache == Tribool::kTrue && StatEq(st, dir.st)) {
+        StatFiles();
+        for (const char* path : dir.unmatched) AddCandidate("new", path);
+        continue;
+      }
+      dir.st = st;
+    }
+
+    arena.Reuse();
+    if (!ListDir(*dir_fd, arena, entries, caps.precompose_unicode, caps.case_sensitive)) {
+      AddUnmached("");
+      continue;
+    }
+    dir.unmatched.clear();
+    dir.arena.Reuse();
+
+    const git_index_entry* const* file = dir.files.data();
+    const git_index_entry* const* file_end = file + dir.files.size();
+    const StringView* subdir = dir.subdirs.data();
+    const StringView* subdir_end = subdir + dir.subdirs.size();
+
+    for (char* entry : entries) {
+      bool matched = false;
+
+      for (; file != file_end; ++file) {
+        int cmp = str.Cmp(Basename(*file), entry);
+        if (cmp < 0) {
+          AddCandidate("deleted", (*file)->path);
+        } else if (cmp == 0) {
+          struct stat st;
+          if (fstatat(*dir_fd, entry, &st, AT_SYMLINK_NOFOLLOW)) {
+            AddCandidate("unreadable", (*file)->path);
+          } else if (IsModified(*file, st, caps)) {
+            AddCandidate(nullptr, (*file)->path);
+          }
+          matched = true;
+          ++file;
+          break;
+        } else {
+          break;
+        }
+      }
+
+      if (matched) continue;
+
+      for (; subdir != subdir_end; ++subdir) {
+        int cmp = str.Cmp(*subdir, entry);
+        if (cmp > 0) break;
+        if (cmp == 0) {
+          matched = true;
+          ++subdir;
+          break;
+        }
+      }
+
+      if (!matched) {
+        StringView basename(entry);
+        if (entry[-1] == DT_DIR) entry[basename.len++] = '/';
+        AddUnmached(basename);
+      }
+    }
+
+    for (; file != file_end; ++file) AddCandidate("deleted", (*file)->path);
+  }
+
+  return dirty_candidates;
+}
+
+}  // namespace
+
+RepoCaps::RepoCaps(git_repository* repo, git_index* index) {
+  trust_filemode = git_index_is_filemode_trustworthy(index);
+  has_symlinks = git_index_supports_symlinks(index);
+  case_sensitive = git_index_is_case_sensitive(index);
+  precompose_unicode = git_index_precompose_unicode(index);
+  LOG(DEBUG) << "Repository capabilities for " << Print(git_repository_workdir(repo)) << ": "
+             << "is_filemode_trustworthy = " << std::boolalpha << trust_filemode << ", "
+             << "index_supports_symlinks = " << std::boolalpha << has_symlinks << ", "
+             << "index_is_case_sensitive = " << std::boolalpha << case_sensitive << ", "
+             << "precompose_unicode = " << std::boolalpha << precompose_unicode;
+}
+
+Index::Index(git_repository* repo, git_index* index)
+    : dirs_(&arena_),
+      splits_(&arena_),
+      git_index_(index),
+      root_dir_(git_repository_workdir(repo)),
+      caps_(repo, index) {
+  size_t total_weight = InitDirs(index);
+  InitSplits(total_weight);
+}
+
+size_t Index::InitDirs(git_index* index) {
+  const Str<> str(git_index_is_case_sensitive(index));
+  const size_t index_size = git_index_entrycount(index);
+  dirs_.reserve(index_size / 8);
+  std::stack<IndexDir*> stack;
+  stack.push(arena_.DirectInit<IndexDir>(&arena_));
+
+  size_t total_weight = 0;
+  auto PopDir = [&] {
+    CHECK(!stack.empty());
+    IndexDir* top = stack.top();
+    CHECK(top->depth + 1 == stack.size());
+    if (!std::is_sorted(top->subdirs.begin(), top->subdirs.end(), str.Lt)) {
+      StrSort(top->subdirs.begin(), top->subdirs.end(), str.case_sensitive);
+    }
+    total_weight += Weight(*top);
+    dirs_.push_back(top);
+    stack.pop();
+  };
+
+  for (size_t i = 0; i != index_size; ++i) {
+    const git_index_entry* entry = git_index_get_byindex_no_sort(index, i);
+    IndexDir* prev = stack.top();
+    size_t common_len, common_depth;
+    CommonDir(str, prev->path.ptr, entry->path, &common_len, &common_depth);
+    CHECK(common_depth <= prev->depth);
+
+    for (size_t i = common_depth; i != prev->depth; ++i) PopDir();
+
+    for (const char* p = entry->path + common_len; (p = std::strchr(p, '/')); ++p) {
+      IndexDir* top = stack.top();
+      StringView subdir(entry->path + top->path.len, p);
+      top->subdirs.push_back(subdir);
+      IndexDir* dir = arena_.DirectInit<IndexDir>(&arena_);
+      dir->path = StringView(entry->path, p - entry->path + 1);
+      dir->basename = subdir;
+      dir->depth = stack.size();
+      CHECK(dir->path.ptr[dir->path.len - 1] == '/');
+      stack.push(dir);
+    }
+
+    CHECK(!stack.empty());
+    IndexDir* dir = stack.top();
+    dir->files.push_back(entry);
+  }
+
+  CHECK(!stack.empty());
+  do {
+    PopDir();
+  } while (!stack.empty());
+  std::reverse(dirs_.begin(), dirs_.end());
+
+  return total_weight;
+}
+
+void Index::InitSplits(size_t total_weight) {
+  constexpr size_t kMinShardWeight = 512;
+  const size_t kNumShards = 16 * GlobalThreadPool()->num_threads();
+  const size_t shard_weight = std::max(kMinShardWeight, total_weight / kNumShards);
+
+  splits_.reserve(kNumShards + 1);
+  splits_.push_back(0);
+
+  for (size_t i = 0, w = 0; i != dirs_.size(); ++i) {
+    w += Weight(*dirs_[i]);
+    if (w >= shard_weight) {
+      w = 0;
+      splits_.push_back(i + 1);
+    }
+  }
+
+  if (splits_.back() != dirs_.size()) splits_.push_back(dirs_.size());
+  CHECK(splits_.size() <= kNumShards + 1);
+  CHECK(std::is_sorted(splits_.begin(), splits_.end()));
+  CHECK(std::adjacent_find(splits_.begin(), splits_.end()) == splits_.end());
+}
+
+std::vector<const char*> Index::GetDirtyCandidates(const ScanOpts& opts) {
+  int root_fd = open(root_dir_, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+  VERIFY(root_fd >= 0);
+  ON_SCOPE_EXIT(&) { CHECK(!close(root_fd)) << Errno(); };
+
+  CHECK(!splits_.empty());
+
+  std::mutex mutex;
+  std::condition_variable cv;
+  size_t inflight = splits_.size() - 1;
+  bool error = false;
+  std::vector<const char*> res;
+
+  for (size_t i = 0; i != splits_.size() - 1; ++i) {
+    size_t from = splits_[i];
+    size_t to = splits_[i + 1];
+
+    GlobalThreadPool()->Schedule([&, from, to]() {
+      ON_SCOPE_EXIT(&) {
+        std::unique_lock<std::mutex> lock(mutex);
+        CHECK(inflight);
+        if (--inflight == 0) cv.notify_one();
+      };
+      try {
+        std::vector<const char*> candidates =
+            ScanDirs(git_index_, root_fd, dirs_.data() + from, dirs_.data() + to, caps_, opts);
+        if (!candidates.empty()) {
+          std::unique_lock<std::mutex> lock(mutex);
+          res.insert(res.end(), candidates.begin(), candidates.end());
+        }
+      } catch (const Exception&) {
+        std::unique_lock<std::mutex> lock(mutex);
+        error = true;
+      }
+    });
+  }
+
+  {
+    std::unique_lock<std::mutex> lock(mutex);
+    while (inflight) cv.wait(lock);
+  }
+
+  VERIFY(!error);
+  StrSort(res.begin(), res.end(), git_index_is_case_sensitive(git_index_));
+  auto StrEq = [](const char* a, const char* b) { return !strcmp(a, b); };
+  res.erase(std::unique(res.begin(), res.end(), StrEq), res.end());
+  return res;
+}
+
+}  // namespace gitstatus
diff --git a/src/index.h b/src/index.h
new file mode 100644
index 00000000..bbf95673
--- /dev/null
+++ b/src/index.h
@@ -0,0 +1,84 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_INDEX_H_
+#define ROMKATV_GITSTATUS_INDEX_H_
+
+#include <sys/stat.h>
+
+#include <git2.h>
+
+#include <cstddef>
+#include <string>
+#include <vector>
+
+#include "arena.h"
+#include "options.h"
+#include "string_view.h"
+#include "tribool.h"
+
+namespace gitstatus {
+
+struct RepoCaps {
+  RepoCaps(git_repository* repo, git_index* index);
+
+  bool trust_filemode;
+  bool has_symlinks;
+  bool case_sensitive;
+  bool precompose_unicode;
+};
+
+struct ScanOpts {
+  bool include_untracked;
+  Tribool untracked_cache;
+};
+
+struct IndexDir {
+  explicit IndexDir(Arena* arena) : files(arena), subdirs(arena) {}
+
+  StringView path;
+  StringView basename;
+  size_t depth = 0;
+  struct stat st = {};
+  WithArena<std::vector<const git_index_entry*>> files;
+  WithArena<std::vector<StringView>> subdirs;
+
+  Arena arena;
+  std::vector<const char*> unmatched;
+};
+
+class Index {
+ public:
+  Index(git_repository* repo, git_index* index);
+
+  std::vector<const char*> GetDirtyCandidates(const ScanOpts& opts);
+
+ private:
+  size_t InitDirs(git_index* index);
+  void InitSplits(size_t total_weight);
+
+  Arena arena_;
+  WithArena<std::vector<IndexDir*>> dirs_;
+  WithArena<std::vector<size_t>> splits_;
+  git_index* git_index_;
+  const char* root_dir_;
+  RepoCaps caps_;
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_GIT_H_
diff --git a/src/logging.cc b/src/logging.cc
new file mode 100644
index 00000000..fb9ac9ea
--- /dev/null
+++ b/src/logging.cc
@@ -0,0 +1,139 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "logging.h"
+
+#include <pthread.h>
+#include <time.h>
+
+#include <cerrno>
+#include <cstdio>
+#include <cstring>
+#include <ctime>
+#include <mutex>
+#include <string>
+
+namespace gitstatus {
+
+namespace internal_logging {
+
+namespace {
+
+std::mutex g_log_mutex;
+
+constexpr char kHexLower[] = {'0', '1', '2', '3', '4', '5', '6', '7',
+                              '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
+
+void FormatThreadId(char (&out)[2 * sizeof(std::uintptr_t) + 1]) {
+  std::uintptr_t tid = (std::uintptr_t)pthread_self();
+  char* p = out + sizeof(out) - 1;
+  *p = 0;
+  do {
+    --p;
+    *p = kHexLower[tid & 0xF];
+    tid >>= 4;
+  } while (p != out);
+}
+
+void FormatCurrentTime(char (&out)[64]) {
+  std::time_t time = std::time(nullptr);
+  struct tm tm;
+  if (localtime_r(&time, &tm) != &tm || std::strftime(out, sizeof(out), "%F %T", &tm) == 0) {
+    std::strcpy(out, "undef");
+  }
+}
+
+}  // namespace
+
+LogStreamBase::LogStreamBase(const char* file, int line, LogLevel lvl)
+    : errno_(errno), file_(file), line_(line), lvl_(LogLevelStr(lvl)) {
+  strm_ = std::make_unique<std::ostringstream>();
+}
+
+void LogStreamBase::Flush() {
+  {
+    std::string msg = strm_->str();
+    char tid[2 * sizeof(std::uintptr_t) + 1];
+    FormatThreadId(tid);
+    char time[64];
+    FormatCurrentTime(time);
+
+    std::unique_lock<std::mutex> lock(g_log_mutex);
+    std::fprintf(stderr, "[%s %s %s %s:%d] %s\n", time, tid, lvl_, file_, line_, msg.c_str());
+  }
+  strm_.reset();
+  errno = errno_;
+}
+
+std::ostream& operator<<(std::ostream& strm, Errno e) {
+  // GNU C Library uses a buffer of 1024 characters for strerror(). Mimic to avoid truncations.
+  char buf[1024];
+  auto x = strerror_r(e.err, buf, sizeof(buf));
+  // There are two versions of strerror_r with different semantics. We can figure out which
+  // one we've got by looking at the result type.
+  if (std::is_same<decltype(x), int>::value) {
+    // XSI-compliant version.
+    strm << (x ? "unknown error" : buf);
+  } else if (std::is_same<decltype(x), char*>::value) {
+    // GNU-specific version.
+    strm << x;
+  } else {
+    // Something else entirely.
+    strm << "unknown error";
+  }
+  return strm;
+}
+
+}  // namespace internal_logging
+
+LogLevel g_min_log_level = INFO;
+
+const char* LogLevelStr(LogLevel lvl) {
+  switch (lvl) {
+    case DEBUG:
+      return "DEBUG";
+    case INFO:
+      return "INFO";
+    case WARN:
+      return "WARN";
+    case ERROR:
+      return "ERROR";
+    case FATAL:
+      return "FATAL";
+  }
+  return "UNKNOWN";
+}
+
+bool ParseLogLevel(const char* s, LogLevel& lvl) {
+  if (!s)
+    return false;
+  else if (!std::strcmp(s, "DEBUG"))
+    lvl = DEBUG;
+  else if (!std::strcmp(s, "INFO"))
+    lvl = INFO;
+  else if (!std::strcmp(s, "WARN"))
+    lvl = WARN;
+  else if (!std::strcmp(s, "ERROR"))
+    lvl = ERROR;
+  else if (!std::strcmp(s, "FATAL"))
+    lvl = FATAL;
+  else
+    return false;
+  return true;
+}
+
+}  // namespace gitstatus
diff --git a/src/logging.h b/src/logging.h
new file mode 100644
index 00000000..6ddb2e16
--- /dev/null
+++ b/src/logging.h
@@ -0,0 +1,124 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_LOGGING_H_
+#define ROMKATV_GITSTATUS_LOGGING_H_
+
+#include <cstdlib>
+#include <memory>
+#include <ostream>
+#include <sstream>
+
+#define LOG(severity) LOG_I(severity)
+
+#define LOG_I(severity)                                                                            \
+  (::gitstatus::severity < ::gitstatus::g_min_log_level)                                           \
+      ? static_cast<void>(0)                                                                       \
+      : ::gitstatus::internal_logging::Assignable() =                                              \
+            ::gitstatus::internal_logging::LogStream<::gitstatus::severity>(__FILE__, __LINE__,    \
+                                                                            ::gitstatus::severity) \
+                .ref()
+
+namespace gitstatus {
+
+enum LogLevel {
+  DEBUG,
+  INFO,
+  WARN,
+  ERROR,
+  FATAL,
+};
+
+const char* LogLevelStr(LogLevel lvl);
+bool ParseLogLevel(const char* s, LogLevel& lvl);
+
+extern LogLevel g_min_log_level;
+
+namespace internal_logging {
+
+struct Assignable {
+  template <class T>
+  void operator=(const T&) const {}
+};
+
+class LogStreamBase {
+ public:
+  LogStreamBase(const char* file, int line, LogLevel lvl);
+
+  LogStreamBase& ref() { return *this; }
+  std::ostream& strm() { return *strm_; }
+  int stashed_errno() const { return errno_; }
+
+ protected:
+  void Flush();
+
+ private:
+  int errno_;
+  const char* file_;
+  int line_;
+  const char* lvl_;
+  std::unique_ptr<std::ostringstream> strm_;
+};
+
+template <LogLevel>
+class LogStream : public LogStreamBase {
+ public:
+  using LogStreamBase::LogStreamBase;
+  ~LogStream() { this->Flush(); }
+};
+
+template <>
+class LogStream<FATAL> : public LogStreamBase {
+ public:
+  using LogStreamBase::LogStreamBase;
+  ~LogStream() __attribute__((noreturn)) {
+    this->Flush();
+    std::abort();
+  }
+};
+
+template <class T>
+LogStreamBase& operator<<(LogStreamBase& strm, const T& val) {
+  strm.strm() << val;
+  return strm;
+}
+
+inline LogStreamBase& operator<<(LogStreamBase& strm, std::ostream& (*manip)(std::ostream&)) {
+  strm.strm() << manip;
+  return strm;
+}
+
+struct Errno {
+  int err;
+};
+
+std::ostream& operator<<(std::ostream& strm, Errno e);
+
+struct StashedErrno {};
+
+inline LogStreamBase& operator<<(LogStreamBase& strm, StashedErrno) {
+  return strm << Errno{strm.stashed_errno()};
+}
+
+}  // namespace internal_logging
+
+inline internal_logging::Errno Errno(int err) { return {err}; }
+inline internal_logging::StashedErrno Errno() { return {}; }
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_LOGGING_H_
diff --git a/src/options.cc b/src/options.cc
new file mode 100644
index 00000000..421e5854
--- /dev/null
+++ b/src/options.cc
@@ -0,0 +1,342 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "options.h"
+
+#include <fnmatch.h>
+#include <getopt.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <climits>
+#include <cstdlib>
+#include <cstring>
+#include <iostream>
+
+#include "print.h"
+
+namespace gitstatus {
+
+namespace {
+
+long ParseLong(const char* s) {
+  errno = 0;
+  char* end = nullptr;
+  long res = std::strtol(s, &end, 10);
+  if (*end || end == s || errno) {
+    std::cerr << "gitstatusd: not an integer: " << s << std::endl;
+    std::exit(10);
+  }
+  return res;
+}
+
+long ParseInt(const char* s) {
+  long res = ParseLong(s);
+  if (res < INT_MIN || res > INT_MAX) {
+    std::cerr << "gitstatusd: integer out of bounds: " << s << std::endl;
+    std::exit(10);
+  }
+  return res;
+}
+
+void PrintUsage() {
+  std::cout << "Usage: gitstatusd [OPTION]...\n"
+            << "Print machine-readable status of the git repos for directores in stdin.\n"
+            << "\n"
+            << "OPTIONS\n"
+            << "  -l, --lock-fd=NUM [default=-1]\n"
+            << "   If non-negative, check whether the specified file descriptor is locked when\n"
+            << "   not receiving any requests for one second; exit if it isn't locked.\n"
+            << "\n"
+            << "  -p, --parent-pid=NUM [default=-1]\n"
+            << "   If non-negative, send signal 0 to the specified PID when not receiving any\n"
+            << "   requests for one second; exit if signal sending fails.\n"
+            << "\n"
+            << "  -t, --num-threads=NUM [default=1]\n"
+            << "   Use this many threads to scan git workdir for unstaged and untracked files.\n"
+            << "   Empirically, setting this parameter to twice the number of virtual CPU yields\n"
+            << "   maximum performance.\n"
+            << "\n"
+            << "  -v, --log-level=STR [default=INFO]\n"
+            << "   Don't write entires to log whose log level is below this. Log levels in\n"
+            << "   increasing order: DEBUG, INFO, WARN, ERROR, FATAL.\n"
+            << "\n"
+            << "  -r, --repo-ttl-seconds=NUM [default=3600]\n"
+            << "   Close git repositories that haven't been used for this long. This is meant to\n"
+            << "   release resources such as memory and file descriptors. The next request for a\n"
+            << "   repo that's been closed is much slower than for a repo that hasn't been.\n"
+            << "   Negative value means infinity.\n"
+            << "\n"
+            << "  -s, --max-num-staged=NUM [default=1]\n"
+            << "   Report at most this many staged changes; negative value means infinity.\n"
+            << "\n"
+            << "  -u, --max-num-unstaged=NUM [default=1]\n"
+            << "   Report at most this many unstaged changes; negative value means infinity.\n"
+            << "\n"
+            << "  -d, --max-num-untracked=NUM [default=1]\n"
+            << "   Report at most this many untracked files; negative value means infinity.\n"
+            << "\n"
+            << "  -m, --dirty-max-index-size=NUM [default=-1]\n"
+            << "   If a repo has more files in its index than this, override --max-num-unstaged\n"
+            << "   and --max-num-untracked (but not --max-num-staged) with zeros; negative value\n"
+            << "   means infinity.\n"
+            << "\n"
+            << "  -e, --recurse-untracked-dirs\n"
+            << "   Count files within untracked directories like `git status --untracked-files`.\n"
+            << "\n"
+            << "  -U, --ignore-status-show-untracked-files\n"
+            << "   Unless this option is specified, report zero untracked files for repositories\n"
+            << "   with status.showUntrackedFiles = false.\n"
+            << "\n"
+            << "  -W, --ignore-bash-show-untracked-files\n"
+            << "   Unless this option is specified, report zero untracked files for repositories\n"
+            << "   with bash.showUntrackedFiles = false.\n"
+            << "\n"
+            << "  -D, --ignore-bash-show-dirty-state\n"
+            << "   Unless this option is specified, report zero staged, unstaged and conflicted\n"
+            << "   changes for repositories with bash.showDirtyState = false.\n"
+            << "\n"
+            << "  -V, --version\n"
+            << "   Print gitstatusd version and exit.\n"
+            << "\n"
+            << "  -G, --version-glob=STR [default=*]\n"
+            << "   Immediately exit with code 11 if gitstatusd version (see --version) doesn't\n"
+            << "   does not match the specified pattern. Matching is done with fnmatch(3)\n"
+            << "   without flags.\n"
+            << "\n"
+            << "  -h, --help\n"
+            << "  Display this help and exit.\n"
+            << "\n"
+            << "INPUT\n"
+            << "\n"
+            << "  Requests are read from stdin, separated by ascii 30 (record separator). Each\n"
+            << "  request is made of the following fields, in the specified order, separated by\n"
+            << "  ascii 31 (unit separator):\n"
+            << "\n"
+            << "    1. Request ID. Any string. Can be empty.\n"
+            << "    2. Path to the directory for which git stats are being requested.\n"
+            << "       If the first character is ':', it is removed and the remaning path\n"
+            << "       is treated as GIT_DIR.\n"
+            << "    3. (Optional) '1' to disable computation of anything that requires reading\n"
+            << "       git index; '0' for the default behavior of computing everything.\n"
+            << "\n"
+            << "OUTPUT\n"
+            << "\n"
+            << "  For every request read from stdin there is response written to stdout.\n"
+            << "  Responses are separated by ascii 30 (record separator). Each response is made\n"
+            << "  of the following fields, in the specified order, separated by ascii 31\n"
+            << "  (unit separator):\n"
+            << "\n"
+            << "     1. Request id. The same as the first field in the request.\n"
+            << "     2. 0 if the directory isn't a git repo, 1 otherwise. If 0, all the\n"
+            << "        following fields are missing.\n"
+            << "     3. Absolute path to the git repository workdir.\n"
+            << "     4. Commit hash that HEAD is pointing to. 40 hex digits.\n"
+            << "     5. Local branch name or empty if not on a branch.\n"
+            << "     6. Upstream branch name. Can be empty.\n"
+            << "     7. The remote name, e.g. \"upstream\" or \"origin\".\n"
+            << "     8. Remote URL. Can be empty.\n"
+            << "     9. Repository state, A.K.A. action. Can be empty.\n"
+            << "    10. The number of files in the index.\n"
+            << "    11. The number of staged changes.\n"
+            << "    12. The number of unstaged changes.\n"
+            << "    13. The number of conflicted changes.\n"
+            << "    14. The number of untracked files.\n"
+            << "    15. Number of commits the current branch is ahead of upstream.\n"
+            << "    16. Number of commits the current branch is behind upstream.\n"
+            << "    17. The number of stashes.\n"
+            << "    18. The last tag (in lexicographical order) that points to the same\n"
+            << "        commit as HEAD.\n"
+            << "    19. The number of unstaged deleted files.\n"
+            << "    20. The number of staged new files.\n"
+            << "    21. The number of staged deleted files.\n"
+            << "    22. The push remote name, e.g. \"upstream\" or \"origin\".\n"
+            << "    23. Push remote URL. Can be empty.\n"
+            << "    24. Number of commits the current branch is ahead of push remote.\n"
+            << "    25. Number of commits the current branch is behind push remote.\n"
+            << "    26. Number of files in the index with skip-worktree bit set.\n"
+            << "    27. Number of files in the index with assume-unchanged bit set.\n"
+            << "\n"
+            << "Note: Renamed files are reported as deleted plus new.\n"
+            << "\n"
+            << "EXAMPLE\n"
+            << "\n"
+            << "  Send a single request and print response (zsh syntax):\n"
+            << "\n"
+            << "    local req_id=id\n"
+            << "    local dir=$PWD\n"
+            << "    echo -nE $req_id$'\\x1f'$dir$'\\x1e' | ./gitstatusd | {\n"
+            << "      local resp\n"
+            << "      IFS=$'\\x1f' read -rd $'\\x1e' -A resp && print -lr -- \"${(@qq)resp}\"\n"
+            << "    }\n"
+            << "\n"
+            << "  Output:"
+            << "\n"
+            << "    'id'\n"
+            << "    '1'\n"
+            << "    '/home/romka/gitstatus'\n"
+            << "    'bf46bf03dbab7108801b53f8a720caee8464c9c3'\n"
+            << "    'master'\n"
+            << "    'master'\n"
+            << "    'origin'\n"
+            << "    'git@github.com:romkatv/gitstatus.git'\n"
+            << "    ''\n"
+            << "    '70'\n"
+            << "    '1'\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "    '2'\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "    ''\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "    ''\n"
+            << "    ''\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "    '0'\n"
+            << "\n"
+            << "EXIT STATUS\n"
+            << "\n"
+            << "  The command returns zero on success (when printing help or on EOF),\n"
+            << "  non-zero on failure. In the latter case the output is unspecified.\n"
+            << "\n"
+            << "COPYRIGHT\n"
+            << "\n"
+            << "  Copyright 2019 Roman Perepelitsa\n"
+            << "  This is free software; see https://github.com/romkatv/gitstatus for copying\n"
+            << "  conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR\n"
+            << "  A PARTICULAR PURPOSE." << std::endl;
+}
+
+const char* Version() {
+#define _INTERNAL_GITSTATUS_STRINGIZE(x) _INTERNAL_GITSTATUS_STRINGIZE_I(x)
+#define _INTERNAL_GITSTATUS_STRINGIZE_I(x) #x
+  return _INTERNAL_GITSTATUS_STRINGIZE(GITSTATUS_VERSION);
+#undef _INTERNAL_GITSTATUS_STRINGIZE_I
+#undef _INTERNAL_GITSTATUS_STRINGIZE
+}
+
+}  // namespace
+
+Options ParseOptions(int argc, char** argv) {
+  const struct option opts[] = {{"help", no_argument, nullptr, 'h'},
+                                {"version", no_argument, nullptr, 'V'},
+                                {"version-glob", no_argument, nullptr, 'G'},
+                                {"lock-fd", required_argument, nullptr, 'l'},
+                                {"parent-pid", required_argument, nullptr, 'p'},
+                                {"num-threads", required_argument, nullptr, 't'},
+                                {"log-level", required_argument, nullptr, 'v'},
+                                {"repo-ttl-seconds", required_argument, nullptr, 'r'},
+                                {"max-num-staged", required_argument, nullptr, 's'},
+                                {"max-num-unstaged", required_argument, nullptr, 'u'},
+                                {"max-num-conflicted", required_argument, nullptr, 'c'},
+                                {"max-num-untracked", required_argument, nullptr, 'd'},
+                                {"dirty-max-index-size", required_argument, nullptr, 'm'},
+                                {"recurse-untracked-dirs", no_argument, nullptr, 'e'},
+                                {"ignore-status-show-untracked-files", no_argument, nullptr, 'U'},
+                                {"ignore-bash-show-untracked-files", no_argument, nullptr, 'W'},
+                                {"ignore-bash-show-dirty-state", no_argument, nullptr, 'D'},
+                                {}};
+  Options res;
+  while (true) {
+    switch (getopt_long(argc, argv, "hVG:l:p:t:v:r:s:u:c:d:m:eUWD", opts, nullptr)) {
+      case -1:
+        if (optind != argc) {
+          std::cerr << "unexpected positional argument: " << argv[optind] << std::endl;
+          std::exit(10);
+        }
+        return res;
+      case 'h':
+        PrintUsage();
+        std::exit(0);
+      case 'V':
+        std::cout << Version() << std::endl;
+        std::exit(0);
+      case 'G':
+        if (int err = fnmatch(optarg, Version(), 0)) {
+          if (err != FNM_NOMATCH) {
+            std::cerr << "Cannot match " << Print(Version()) << " against pattern "
+                                         << Print(optarg) << ": error " << err;
+            std::exit(10);
+          }
+          std::cerr << "Version mismatch. Wanted (pattern): " << Print(optarg)
+                    << ". Actual: " << Print(Version()) << "." << std::endl;
+          std::exit(11);
+        }
+        break;
+      case 'l':
+        res.lock_fd = ParseInt(optarg);
+        break;
+      case 'p':
+        res.parent_pid = ParseInt(optarg);
+        break;
+      case 'v':
+        if (!ParseLogLevel(optarg, res.log_level)) {
+          std::cerr << "invalid log level: " << optarg << std::endl;
+          std::exit(10);
+        }
+        break;
+      case 'r':
+        res.repo_ttl = std::chrono::seconds(ParseLong(optarg));
+        break;
+      case 't': {
+        long n = ParseLong(optarg);
+        if (n <= 0) {
+          std::cerr << "invalid number of threads: " << n << std::endl;
+          std::exit(10);
+        }
+        res.num_threads = n;
+        break;
+      }
+      case 's':
+        res.max_num_staged = ParseLong(optarg);
+        break;
+      case 'u':
+        res.max_num_unstaged = ParseLong(optarg);
+        break;
+      case 'c':
+        res.max_num_conflicted = ParseLong(optarg);
+        break;
+      case 'd':
+        res.max_num_untracked = ParseLong(optarg);
+        break;
+      case 'm':
+        res.dirty_max_index_size = ParseLong(optarg);
+        break;
+      case 'e':
+        res.recurse_untracked_dirs = true;
+        break;
+      case 'U':
+        res.ignore_status_show_untracked_files = true;
+        break;
+      case 'W':
+        res.ignore_bash_show_untracked_files = true;
+        break;
+      case 'D':
+        res.ignore_bash_show_dirty_state = true;
+        break;
+      default:
+        std::exit(10);
+    }
+  }
+}
+
+}  // namespace gitstatus
diff --git a/src/options.h b/src/options.h
new file mode 100644
index 00000000..7cbfeed8
--- /dev/null
+++ b/src/options.h
@@ -0,0 +1,76 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_OPTIONS_H_
+#define ROMKATV_GITSTATUS_OPTIONS_H_
+
+#include <chrono>
+#include <string>
+
+#include "logging.h"
+#include "time.h"
+
+namespace gitstatus {
+
+struct Limits {
+  // Report at most this many staged changes.
+  size_t max_num_staged = 1;
+  // Report at most this many unstaged changes.
+  size_t max_num_unstaged = 1;
+  // Report at most this many conflicted changes.
+  size_t max_num_conflicted = 1;
+  // Report at most this many untracked files.
+  size_t max_num_untracked = 1;
+  // If a repo has more files in its index than this, override max_num_unstaged and
+  // max_num_untracked (but not max_num_staged) with zeros.
+  size_t dirty_max_index_size = -1;
+  // If true, report untracked files like `git status --untracked-files`.
+  bool recurse_untracked_dirs = false;
+  // Unless true, report zero untracked files for repositories with
+  // status.showUntrackedFiles = false.
+  bool ignore_status_show_untracked_files = false;
+  // Unless true, report zero untracked files for repositories with
+  // bash.showUntrackedFiles = false.
+  bool ignore_bash_show_untracked_files = false;
+  // Unless true, report zero staged, unstaged and conflicted changes for repositories with
+  // bash.showDirtyState = false.
+  bool ignore_bash_show_dirty_state = false;
+};
+
+struct Options : Limits {
+  // Use this many threads to scan git workdir for unstaged and untracked files. Must be positive.
+  size_t num_threads = 1;
+  // If non-negative, check whether the specified file descriptor is locked when not receiving any
+  // requests for one second; exit if it isn't locked.
+  int lock_fd = -1;
+  // If non-negative, send signal 0 to the specified PID when not receiving any requests for one
+  // second; exit if signal sending fails.
+  int parent_pid = -1;
+  // Don't write entires to log whose log level is below this. Log levels in increasing order:
+  // DEBUG, INFO, WARN, ERROR, FATAL.
+  LogLevel log_level = INFO;
+  // Close git repositories that haven't been used for this long. This is meant to release resources
+  // such as memory and file descriptors. The next request for a repo that's been closed is much
+  // slower than for a repo that hasn't been. Negative value means infinity.
+  Duration repo_ttl = std::chrono::seconds(3600);
+};
+
+Options ParseOptions(int argc, char** argv);
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_OPTIONS_H_
diff --git a/src/print.h b/src/print.h
new file mode 100644
index 00000000..949f946b
--- /dev/null
+++ b/src/print.h
@@ -0,0 +1,101 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_PRINT_H_
+#define ROMKATV_GITSTATUS_PRINT_H_
+
+#include <sys/stat.h>
+
+#include <iomanip>
+#include <ostream>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include <git2.h>
+
+#include "string_view.h"
+#include "strings.h"
+
+namespace gitstatus {
+
+template <class T>
+struct Printable {
+  const T& value;
+};
+
+template <class T>
+Printable<T> Print(const T& val) {
+  return {val};
+}
+
+template <class T>
+std::ostream& operator<<(std::ostream& strm, const Printable<T>& p) {
+  static_assert(!std::is_pointer<std::decay_t<T>>(), "");
+  return strm << p.value;
+}
+
+inline std::ostream& operator<<(std::ostream& strm, const Printable<StringView>& p) {
+  Quote(strm, p.value.ptr, p.value.ptr + p.value.len);
+  return strm;
+}
+
+inline std::ostream& operator<<(std::ostream& strm, const Printable<std::string>& p) {
+  Quote(strm, p.value.data(), p.value.data() + p.value.size());
+  return strm;
+}
+
+inline std::ostream& operator<<(std::ostream& strm, const Printable<const char*>& p) {
+  Quote(strm, p.value, p.value ? p.value + std::strlen(p.value) : nullptr);
+  return strm;
+}
+
+inline std::ostream& operator<<(std::ostream& strm, const Printable<char*>& p) {
+  Quote(strm, p.value, p.value ? p.value + std::strlen(p.value) : nullptr);
+  return strm;
+}
+
+template <class T, class U>
+std::ostream& operator<<(std::ostream& strm, const Printable<std::pair<T, U>>& p) {
+  return strm << '{' << Print(p.value.first) << ", " << Print(p.value.second) << '}';
+}
+
+template <class T>
+std::ostream& operator<<(std::ostream& strm, const Printable<std::vector<T>>& p) {
+  strm << '[';
+  for (size_t i = 0; i != p.value.size(); ++i) {
+    if (i) strm << ", ";
+    strm << Print(p.value[i]);
+  }
+  strm << ']';
+  return strm;
+}
+
+inline std::ostream& operator<<(std::ostream& strm, const Printable<struct timespec>& p) {
+  strm << p.value.tv_sec << '.' << std::setw(9) << std::setfill('0') << p.value.tv_nsec;
+  return strm;
+}
+
+inline std::ostream& operator<<(std::ostream& strm, const Printable<git_index_time>& p) {
+  strm << p.value.seconds << '.' << std::setw(9) << std::setfill('0') << p.value.nanoseconds;
+  return strm;
+}
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_PRINT_H_
diff --git a/src/repo.cc b/src/repo.cc
new file mode 100644
index 00000000..d7ea7d3e
--- /dev/null
+++ b/src/repo.cc
@@ -0,0 +1,503 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "repo.h"
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <atomic>
+#include <cstdlib>
+#include <cstring>
+#include <exception>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+#include "arena.h"
+#include "check.h"
+#include "check_dir_mtime.h"
+#include "dir.h"
+#include "git.h"
+#include "print.h"
+#include "scope_guard.h"
+#include "stat.h"
+#include "string_cmp.h"
+#include "thread_pool.h"
+#include "timer.h"
+
+namespace gitstatus {
+
+namespace {
+
+using namespace std::string_literals;
+
+template <class T>
+T Load(const std::atomic<T>& x) {
+  return x.load(std::memory_order_relaxed);
+}
+
+template <class T>
+void Store(std::atomic<T>& x, T v) {
+  x.store(v, std::memory_order_relaxed);
+}
+
+template <class T>
+T Inc(std::atomic<T>& x, T by = 1) {
+  return x.fetch_add(by, std::memory_order_relaxed);
+}
+
+template <class T>
+T Dec(std::atomic<T>& x) {
+  return x.fetch_sub(1, std::memory_order_relaxed);
+}
+
+template <class T>
+T Exchange(std::atomic<T>& x, T v) {
+  return x.exchange(v, std::memory_order_relaxed);
+}
+
+const char* DeltaStr(git_delta_t t) {
+  switch (t) {
+    case GIT_DELTA_UNMODIFIED: return "unmodified";
+    case GIT_DELTA_ADDED: return "added";
+    case GIT_DELTA_DELETED: return "deleted";
+    case GIT_DELTA_MODIFIED: return "modified";
+    case GIT_DELTA_RENAMED: return "renamed";
+    case GIT_DELTA_COPIED: return "copied";
+    case GIT_DELTA_IGNORED: return "ignored";
+    case GIT_DELTA_UNTRACKED: return "untracked";
+    case GIT_DELTA_TYPECHANGE: return "typechange";
+    case GIT_DELTA_UNREADABLE: return "unreadable";
+    case GIT_DELTA_CONFLICTED: return "conflicted";
+  }
+  return "unknown";
+}
+
+}  // namespace
+
+bool Repo::Shard::Contains(Str<> str, StringView path) const {
+  if (str.Lt(path, start_s)) return false;
+  if (end_s.empty()) return true;
+  path.len = std::min(path.len, end_s.size());
+  return !str.Lt(end_s, path);
+}
+
+Repo::Repo(git_repository* repo, Limits lim) : lim_(std::move(lim)), repo_(repo), tag_db_(repo) {
+  if (lim_.max_num_untracked) {
+    GlobalThreadPool()->Schedule([this] {
+      bool check = CheckDirMtime(git_repository_path(repo_));
+      std::unique_lock<std::mutex> lock(mutex_);
+      CHECK(Load(untracked_cache_) == Tribool::kUnknown);
+      Store(untracked_cache_, check ? Tribool::kTrue : Tribool::kFalse);
+      cv_.notify_one();
+    });
+  } else {
+    untracked_cache_ = Tribool::kFalse;
+  }
+}
+
+Repo::~Repo() {
+  {
+    std::unique_lock<std::mutex> lock(mutex_);
+    while (untracked_cache_ == Tribool::kUnknown) cv_.wait(lock);
+  }
+  if (git_index_) git_index_free(git_index_);
+  git_repository_free(repo_);
+}
+
+IndexStats Repo::GetIndexStats(const git_oid* head, git_config* cfg) {
+  ON_SCOPE_EXIT(this, orig_lim = lim_) { lim_ = orig_lim; };
+  auto Off = [&](const char* name) {
+    int val;
+    if (git_config_get_bool(&val, cfg, name) || val) return false;
+    LOG(INFO) << "Honoring git config option: " << name << " = false";
+    return true;
+  };
+  if (!lim_.ignore_status_show_untracked_files && Off("status.showUntrackedFiles")) {
+    lim_.max_num_untracked = 0;
+  }
+  if (!lim_.ignore_bash_show_untracked_files && Off("bash.showUntrackedFiles")) {
+    lim_.max_num_untracked = 0;
+  }
+  if (!lim_.ignore_bash_show_dirty_state && Off("bash.showDirtyState")) {
+    lim_.max_num_staged = 0;
+    lim_.max_num_unstaged = 0;
+    lim_.max_num_conflicted = 0;
+  }
+
+  if (git_index_) {
+    int new_index;
+    VERIFY(!git_index_read_ex(git_index_, 0, &new_index)) << GitError();
+    if (new_index) {
+      head_ = {};
+      index_.reset();
+    }
+  } else {
+    VERIFY(!git_repository_index(&git_index_, repo_)) << GitError();
+    // Query an attribute (doesn't matter which) to initialize repo's attribute
+    // cache. It's a workaround for synchronization bugs (data races) in libgit2
+    // that result from lazy cache initialization without synchrnonization.
+    // Thankfully, subsequent cache reads and writes are properly synchronized.
+    const char* attr;
+    VERIFY(!git_attr_get(&attr, repo_, 0, "x", "x")) << GitError();
+  }
+
+  UpdateShards();
+  Store(error_, false);
+  Store(unstaged_, {});
+  Store(untracked_, {});
+  Store(unstaged_deleted_, {});
+
+  std::vector<const char*> dirty_candidates;
+  const size_t index_size = git_index_entrycount(git_index_);
+
+  if (!lim_.max_num_staged && !lim_.max_num_conflicted) {
+    head_ = {};
+    Store(staged_, {});
+    Store(conflicted_, {});
+    Store(staged_new_, {});
+    Store(staged_deleted_, {});
+    Store(skip_worktree_, {});
+    Store(assume_unchanged_, {});
+  } else if (head) {
+    if (git_oid_equal(head, &head_)) {
+      LOG(INFO) << "Index and HEAD unchanged; staged = " << Load(staged_)
+                << ", conflicted = " << Load(conflicted_);
+    } else {
+      head_ = *head;
+      Store(staged_, {});
+      Store(conflicted_, {});
+      Store(staged_new_, {});
+      Store(staged_deleted_, {});
+      Store(skip_worktree_, {});
+      Store(assume_unchanged_, {});
+      StartStagedScan(head);
+    }
+  } else {
+    head_ = {};
+    size_t staged = 0;
+    size_t skip_worktree = 0;
+    size_t assume_unchanged = 0;
+    for (size_t i = 0; i != index_size; ++i) {
+      const git_index_entry* entry = git_index_get_byindex_no_sort(git_index_, i);
+      if (!(entry->flags_extended & GIT_INDEX_ENTRY_INTENT_TO_ADD)) ++staged;
+      if (entry->flags_extended & GIT_INDEX_ENTRY_SKIP_WORKTREE) ++skip_worktree;
+      if (entry->flags & GIT_INDEX_ENTRY_VALID) ++assume_unchanged;
+    }
+    Store(staged_, staged);
+    Store(conflicted_, {});
+    Store(staged_new_, staged);
+    Store(staged_deleted_, {});
+    Store(skip_worktree_, skip_worktree);
+    Store(assume_unchanged_, assume_unchanged);
+  }
+
+  if (index_size <= lim_.dirty_max_index_size &&
+      (lim_.max_num_unstaged || lim_.max_num_untracked)) {
+    if (!index_) index_ = std::make_unique<Index>(repo_, git_index_);
+    dirty_candidates = index_->GetDirtyCandidates({.include_untracked = lim_.max_num_untracked > 0,
+                                                   .untracked_cache = Load(untracked_cache_)});
+    if (dirty_candidates.empty()) {
+      LOG(INFO) << "Clean repo: no dirty candidates";
+    } else {
+      LOG(INFO) << "Found " << dirty_candidates.size() << " dirty candidate(s) spanning from "
+                << Print(dirty_candidates.front()) << " to " << Print(dirty_candidates.back());
+    }
+    StartDirtyScan(dirty_candidates);
+  }
+
+  Wait();
+  VERIFY(!Load(error_));
+
+  size_t num_staged = std::min(Load(staged_), lim_.max_num_staged);
+  size_t num_unstaged = std::min(Load(unstaged_), lim_.max_num_unstaged);
+  return {.index_size = index_size,
+          .num_staged = num_staged,
+          .num_unstaged = num_unstaged,
+          .num_conflicted = std::min(Load(conflicted_), lim_.max_num_conflicted),
+          .num_untracked = std::min(Load(untracked_), lim_.max_num_untracked),
+          .num_staged_new = std::min(Load(staged_new_), num_staged),
+          .num_staged_deleted = std::min(Load(staged_deleted_), num_staged),
+          .num_unstaged_deleted = std::min(Load(unstaged_deleted_), num_unstaged),
+          .num_skip_worktree = Load(skip_worktree_),
+          .num_assume_unchanged = Load(assume_unchanged_)};
+}
+
+int Repo::OnDelta(const char* type, const git_diff_delta& d, std::atomic<size_t>& c1, size_t m1,
+                  const std::atomic<size_t>& c2, size_t m2) {
+  auto Msg = [&]() {
+    const char* status = DeltaStr(d.status);
+    std::ostringstream strm;
+    strm << "Found " << type << " file";
+    if (strcmp(status, type)) strm << " (" << status << ")";
+    strm << ": " << Print(d.new_file.path);
+    return strm.str();
+  };
+
+  size_t v = Inc(c1);
+  if (v) {
+    LOG(DEBUG) << Msg();
+  } else {
+    LOG(INFO) << Msg();
+  }
+  if (v + 1 < m1) return GIT_DIFF_DELTA_DO_NOT_INSERT;
+  if (Load(c2) < m2) return GIT_DIFF_DELTA_DO_NOT_INSERT | GIT_DIFF_DELTA_SKIP_TYPE;
+  return GIT_EUSER;
+}
+
+void Repo::StartDirtyScan(const std::vector<const char*>& paths) {
+  if (paths.empty()) return;
+
+  git_diff_options opt = GIT_DIFF_OPTIONS_INIT;
+  opt.payload = this;
+  opt.flags = GIT_DIFF_INCLUDE_TYPECHANGE_TREES | GIT_DIFF_SKIP_BINARY_CHECK |
+              GIT_DIFF_DISABLE_PATHSPEC_MATCH | GIT_DIFF_EXEMPLARS;
+  if (lim_.max_num_untracked) {
+    opt.flags |= GIT_DIFF_INCLUDE_UNTRACKED;
+    if (lim_.recurse_untracked_dirs) opt.flags |= GIT_DIFF_RECURSE_UNTRACKED_DIRS;
+  } else {
+    opt.flags |= GIT_DIFF_ENABLE_FAST_UNTRACKED_DIRS;
+  }
+  opt.ignore_submodules = GIT_SUBMODULE_IGNORE_DIRTY;
+  opt.notify_cb = +[](const git_diff* diff, const git_diff_delta* delta,
+                      const char* matched_pathspec, void* payload) -> int {
+    if (delta->status == GIT_DELTA_CONFLICTED) return GIT_DIFF_DELTA_DO_NOT_INSERT;
+    Repo* repo = static_cast<Repo*>(payload);
+    if (Load(repo->error_)) return GIT_EUSER;
+    if (delta->status == GIT_DELTA_UNTRACKED) {
+      return repo->OnDelta("untracked", *delta, repo->untracked_, repo->lim_.max_num_untracked,
+                           repo->unstaged_, repo->lim_.max_num_unstaged);
+    } else {
+      if (delta->status == GIT_DELTA_DELETED) Inc(repo->unstaged_deleted_);
+      return repo->OnDelta("unstaged", *delta, repo->unstaged_, repo->lim_.max_num_unstaged,
+                           repo->untracked_, repo->lim_.max_num_untracked);
+    }
+  };
+
+  const Str<> str(git_index_is_case_sensitive(git_index_));
+  auto shard = shards_.begin();
+  for (auto p = paths.begin(); p != paths.end();) {
+    opt.range_start = *p;
+    opt.range_end = *p;
+    opt.pathspec.strings = const_cast<char**>(&*p);
+    opt.pathspec.count = 1;
+    while (!shard->Contains(str, StringView(*p))) ++shard;
+    while (++p != paths.end() && shard->Contains(str, StringView(*p))) {
+      opt.range_end = *p;
+      ++opt.pathspec.count;
+    }
+    RunAsync([this, opt]() {
+      git_diff* diff = nullptr;
+      LOG(DEBUG) << "git_diff_index_to_workdir from " << Print(opt.range_start) << " to "
+                 << Print(opt.range_end);
+      switch (git_diff_index_to_workdir(&diff, repo_, git_index_, &opt)) {
+        case 0:
+          git_diff_free(diff);
+          break;
+        case GIT_EUSER:
+          break;
+        default:
+          LOG(ERROR) << "git_diff_index_to_workdir: " << GitError();
+          throw Exception();
+      }
+    });
+  }
+}
+
+void Repo::StartStagedScan(const git_oid* head) {
+  git_commit* commit = nullptr;
+  VERIFY(!git_commit_lookup(&commit, repo_, head)) << GitError();
+  ON_SCOPE_EXIT(=) { git_commit_free(commit); };
+  git_tree* tree = nullptr;
+  VERIFY(!git_commit_tree(&tree, commit)) << GitError();
+
+  git_diff_options opt = GIT_DIFF_OPTIONS_INIT;
+  opt.flags = GIT_DIFF_EXEMPLARS | GIT_DIFF_INCLUDE_TYPECHANGE_TREES;
+  opt.payload = this;
+  opt.notify_cb = +[](const git_diff* diff, const git_diff_delta* delta,
+                      const char* matched_pathspec, void* payload) -> int {
+    Repo* repo = static_cast<Repo*>(payload);
+    if (Load(repo->error_)) return GIT_EUSER;
+    if (delta->status == GIT_DELTA_CONFLICTED) {
+      return repo->OnDelta("conflicted", *delta, repo->conflicted_, repo->lim_.max_num_conflicted,
+                           repo->staged_, repo->lim_.max_num_staged);
+    } else {
+      if (delta->status == GIT_DELTA_ADDED) Inc(repo->staged_new_);
+      if (delta->status == GIT_DELTA_DELETED) Inc(repo->staged_deleted_);
+      return repo->OnDelta("staged", *delta, repo->staged_, repo->lim_.max_num_staged,
+                           repo->conflicted_, repo->lim_.max_num_conflicted);
+    }
+  };
+
+  for (const Shard& shard : shards_) {
+    RunAsync([this, tree, opt, shard]() mutable {
+      size_t skip_worktree = 0;
+      size_t assume_unchanged = 0;
+      for (size_t i = shard.start_i; i != shard.end_i; ++i) {
+        const git_index_entry* entry = git_index_get_byindex_no_sort(git_index_, i);
+        if (entry->flags_extended & GIT_INDEX_ENTRY_SKIP_WORKTREE) ++skip_worktree;
+        if (entry->flags & GIT_INDEX_ENTRY_VALID) ++assume_unchanged;
+      }
+      Inc(skip_worktree_, skip_worktree);
+      Inc(assume_unchanged_, assume_unchanged);
+      opt.range_start = shard.start_s.c_str();
+      opt.range_end = shard.end_s.c_str();
+      git_diff* diff = nullptr;
+      LOG(DEBUG) << "git_diff_tree_to_index from " << Print(opt.range_start) << " to "
+                 << Print(opt.range_end);
+      switch (git_diff_tree_to_index(&diff, repo_, tree, git_index_, &opt)) {
+        case 0:
+          git_diff_free(diff);
+          break;
+        case GIT_EUSER:
+          break;
+        default:
+          LOG(ERROR) << "git_diff_tree_to_index: " << GitError();
+          throw Exception();
+      }
+    });
+  }
+}
+
+void Repo::UpdateShards() {
+  constexpr size_t kEntriesPerShard = 512;
+
+  const Str<> str(git_index_is_case_sensitive(git_index_));
+  size_t index_size = git_index_entrycount(git_index_);
+  ON_SCOPE_EXIT(&) {
+    LOG(INFO) << "Splitting " << index_size << " object(s) into " << shards_.size() << " shard(s)";
+  };
+
+  if (index_size <= kEntriesPerShard || GlobalThreadPool()->num_threads() < 2) {
+    shards_ = {{
+      .start_s = "",
+      .end_s = "",
+      .start_i = 0,
+      .end_i = index_size}};
+    return;
+  }
+
+  size_t shards =
+      std::min(index_size / kEntriesPerShard + 1, 2 * GlobalThreadPool()->num_threads());
+  shards_.clear();
+  shards_.reserve(shards);
+  std::string last_s;
+  size_t last_i = 0;
+
+  for (size_t i = 0; i != shards - 1; ++i) {
+    size_t idx = (i + 1) * index_size / shards;
+    std::string split = git_index_get_byindex_no_sort(git_index_, idx)->path;
+    auto pos = split.find_last_of('/');
+    if (pos == std::string::npos) continue;
+    split = split.substr(0, pos + 1);
+    Shard shard;
+    shard.end_s = split;
+    --shard.end_s.back();
+    if (!str.Lt(last_s, shard.end_s)) continue;
+    shard.start_s = std::move(last_s);
+    last_s = std::move(split);
+    shard.start_i = last_i;
+    shard.end_i = idx;
+    last_i = idx;
+    shards_.push_back(std::move(shard));
+  }
+  shards_.push_back({
+    .start_s = std::move(last_s),
+    .end_s = "",
+    .start_i = last_i,
+    .end_i = index_size});
+
+  CHECK(!shards_.empty());
+  CHECK(shards_.size() <= shards);
+  CHECK(shards_.front().start_s.empty());
+  CHECK(shards_.front().start_i == 0);
+  CHECK(shards_.back().end_s.empty());
+  CHECK(shards_.back().end_i == index_size);
+  for (size_t i = 0; i != shards_.size(); ++i) {
+    if (i) {
+      const git_index_entry* entry = git_index_get_byindex_no_sort(git_index_, shards_[i].start_i);
+      CHECK(!std::memcmp(shards_[i].start_s.c_str(), entry->path, shards_[i].start_s.size()));
+      CHECK(str.Lt(shards_[i - 1].end_s, shards_[i].start_s));
+      CHECK(shards_[i - 1].end_i == shards_[i].start_i);
+    }
+    if (i != shards_.size() - 1) {
+      CHECK(shards_[i].start_i < shards_[i].end_i);
+      CHECK(str.Lt(shards_[i].start_s, shards_[i].end_s));
+    }
+  }
+}
+
+void Repo::DecInflight() {
+  std::unique_lock<std::mutex> lock(mutex_);
+  CHECK(Load(inflight_) > 0);
+  if (Dec(inflight_) == 1) cv_.notify_one();
+}
+
+void Repo::RunAsync(std::function<void()> f) {
+  Inc(inflight_);
+  try {
+    GlobalThreadPool()->Schedule([this, f = std::move(f)] {
+      try {
+        ON_SCOPE_EXIT(&) { DecInflight(); };
+        f();
+      } catch (const Exception&) {
+        if (!Load(error_)) {
+          std::unique_lock<std::mutex> lock(mutex_);
+          if (!Load(error_)) {
+            Store(error_, true);
+            cv_.notify_one();
+          }
+        }
+      }
+    });
+  } catch (...) {
+    DecInflight();
+    throw;
+  }
+}
+
+void Repo::Wait() {
+  std::unique_lock<std::mutex> lock(mutex_);
+  while (inflight_) cv_.wait(lock);
+}
+
+std::future<std::string> Repo::GetTagName(const git_oid* target) {
+  auto* promise = new std::promise<std::string>;
+  std::future<std::string> res = promise->get_future();
+
+  GlobalThreadPool()->Schedule([=] {
+    ON_SCOPE_EXIT(&) { delete promise; };
+    if (!target) {
+      promise->set_value("");
+      return;
+    }
+    try {
+      promise->set_value(tag_db_.TagForCommit(*target));
+    } catch (const Exception&) {
+      promise->set_exception(std::current_exception());
+    }
+  });
+
+  return res;
+}
+
+}  // namespace gitstatus
diff --git a/src/repo.h b/src/repo.h
new file mode 100644
index 00000000..f243f86e
--- /dev/null
+++ b/src/repo.h
@@ -0,0 +1,126 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_REPO_H_
+#define ROMKATV_GITSTATUS_REPO_H_
+
+#include <stddef.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <git2.h>
+
+#include <algorithm>
+#include <atomic>
+#include <condition_variable>
+#include <cstddef>
+#include <cstring>
+#include <functional>
+#include <future>
+#include <memory>
+#include <mutex>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "check.h"
+#include "index.h"
+#include "options.h"
+#include "string_cmp.h"
+#include "tag_db.h"
+#include "time.h"
+
+namespace gitstatus {
+
+struct IndexStats {
+  size_t index_size = 0;
+  size_t num_staged = 0;
+  size_t num_unstaged = 0;
+  size_t num_conflicted = 0;
+  size_t num_untracked = 0;
+  size_t num_staged_new = 0;
+  size_t num_staged_deleted = 0;
+  size_t num_unstaged_deleted = 0;
+  size_t num_skip_worktree = 0;
+  size_t num_assume_unchanged = 0;
+};
+
+class Repo {
+ public:
+  explicit Repo(git_repository* repo, Limits lim);
+  Repo(Repo&& other) = delete;
+  ~Repo();
+
+  git_repository* repo() const { return repo_; }
+
+  // Head can be null, in which case has_staged will be false.
+  IndexStats GetIndexStats(const git_oid* head, git_config* cfg);
+
+  // Returns the last tag in lexicographical order whose target is equal to the given, or an
+  // empty string. Target can be null, in which case the tag is empty.
+  std::future<std::string> GetTagName(const git_oid* target);
+
+ private:
+  struct Shard {
+    bool Contains(Str<> str, StringView path) const;
+    std::string start_s;
+    std::string end_s;
+    size_t start_i;
+    size_t end_i;
+  };
+
+  void UpdateShards();
+
+  int OnDelta(const char* type, const git_diff_delta& d, std::atomic<size_t>& c1, size_t m1,
+              const std::atomic<size_t>& c2, size_t m2);
+
+  void StartStagedScan(const git_oid* head);
+  void StartDirtyScan(const std::vector<const char*>& paths);
+
+  void DecInflight();
+  void RunAsync(std::function<void()> f);
+  void Wait();
+
+  Limits lim_;
+  git_repository* const repo_;
+  git_index* git_index_ = nullptr;
+  std::vector<Shard> shards_;
+  git_oid head_ = {};
+  TagDb tag_db_;
+
+  std::unique_ptr<Index> index_;
+
+  std::mutex mutex_;
+  std::condition_variable cv_;
+  std::atomic<size_t> inflight_{0};
+  std::atomic<bool> error_{false};
+  std::atomic<size_t> staged_{0};
+  std::atomic<size_t> unstaged_{0};
+  std::atomic<size_t> conflicted_{0};
+  std::atomic<size_t> untracked_{0};
+  std::atomic<size_t> staged_new_{0};
+  std::atomic<size_t> staged_deleted_{0};
+  std::atomic<size_t> unstaged_deleted_{0};
+  std::atomic<size_t> skip_worktree_{0};
+  std::atomic<size_t> assume_unchanged_{0};
+  std::atomic<Tribool> untracked_cache_{Tribool::kUnknown};
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_REPO_H_
diff --git a/src/repo_cache.cc b/src/repo_cache.cc
new file mode 100644
index 00000000..d7f5f9ad
--- /dev/null
+++ b/src/repo_cache.cc
@@ -0,0 +1,167 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "repo_cache.h"
+
+#include <cstring>
+
+#include "check.h"
+#include "git.h"
+#include "print.h"
+#include "scope_guard.h"
+#include "string_view.h"
+
+namespace gitstatus {
+
+namespace {
+
+void GitDirs(const char* dir, bool from_dotgit, std::string& gitdir, std::string& workdir) {
+  git_buf gitdir_buf = {};
+  git_buf workdir_buf = {};
+  ON_SCOPE_EXIT(&) {
+    git_buf_free(&gitdir_buf);
+    git_buf_free(&workdir_buf);
+  };
+  int flags = from_dotgit ? GIT_REPOSITORY_OPEN_NO_SEARCH | GIT_REPOSITORY_OPEN_NO_DOTGIT : 0;
+  switch (git_repository_discover_ex(&gitdir_buf, &workdir_buf, NULL, NULL, dir, flags, nullptr)) {
+    case 0:
+      gitdir.assign(gitdir_buf.ptr, gitdir_buf.size);
+      workdir.assign(workdir_buf.ptr, workdir_buf.size);
+      VERIFY(!gitdir.empty() && gitdir.front() == '/' && gitdir.back() == '/');
+      VERIFY(!workdir.empty() && workdir.front() == '/' && workdir.back() == '/');
+      break;
+    case GIT_ENOTFOUND:
+      gitdir.clear();
+      workdir.clear();
+      break;
+    default:
+      LOG(ERROR) << "git_repository_open_ext: " << Print(dir) << ": " << GitError();
+      throw Exception();
+  }
+}
+
+git_repository* OpenRepo(const std::string& dir, bool from_dotgit) {
+  git_repository* repo = nullptr;
+  int flags = from_dotgit ? GIT_REPOSITORY_OPEN_NO_SEARCH | GIT_REPOSITORY_OPEN_NO_DOTGIT : 0;
+  switch (git_repository_open_ext(&repo, dir.c_str(), flags, nullptr)) {
+    case 0:
+      return repo;
+    case GIT_ENOTFOUND:
+      return nullptr;
+    default:
+      LOG(ERROR) << "git_repository_open_ext: " << Print(dir) << ": " << GitError();
+      throw Exception();
+  }
+}
+
+std::string DirName(std::string path) {
+  if (path.empty()) return "";
+  while (path.back() == '/') {
+    path.pop_back();
+    if (path.empty()) return "";
+  }
+  do {
+    path.pop_back();
+    if (path.empty()) return "";
+  } while (path.back() != '/');
+  return path;
+}
+
+}  // namespace
+
+Repo* RepoCache::Open(const std::string& dir, bool from_dotgit) {
+  if (dir.empty() || dir.front() != '/') return nullptr;
+
+  std::string gitdir, workdir;
+  GitDirs(dir.c_str(), from_dotgit, gitdir, workdir);
+  if (gitdir.empty()) {
+    // This isn't quite correct because of differences in canonicalization, .git files and GIT_DIR.
+    // A proper solution would require tracking the "discovery dir" for every repository and
+    // performing path canonicalization.
+    if (from_dotgit) {
+      Erase(cache_.find(dir.back() == '/' ? dir : dir + '/'));
+    } else {
+      std::string path = dir;
+      if (path.back() != '/') path += '/';
+      do {
+        Erase(cache_.find(path + ".git/"));
+        path = DirName(path);
+      } while (!path.empty());
+    }
+    return nullptr;
+  }
+
+  auto it = cache_.find(gitdir);
+  if (it != cache_.end()) {
+    lru_.erase(it->second->lru);
+    it->second->lru = lru_.insert({Clock::now(), it});
+    return it->second.get();
+  }
+
+  // Opening from gitdir is faster but we cannot use it when gitdir came from a .git file.
+  git_repository* repo =
+      DirName(gitdir) == workdir ? OpenRepo(gitdir, true) : OpenRepo(dir, from_dotgit);
+  if (!repo) return nullptr;
+  ON_SCOPE_EXIT(&) {
+    if (repo) git_repository_free(repo);
+  };
+  if (git_repository_is_bare(repo)) return nullptr;
+  workdir = git_repository_workdir(repo) ?: "";
+  if (workdir.empty()) return nullptr;
+  VERIFY(workdir.front() == '/' && workdir.back() == '/') << Print(workdir);
+
+  auto x = cache_.emplace(gitdir, nullptr);
+  std::unique_ptr<Entry>& elem = x.first->second;
+  if (elem) {
+    lru_.erase(elem->lru);
+  } else {
+    LOG(INFO) << "Initializing new repository: " << Print(gitdir);
+
+    // Libgit2 initializes odb and refdb lazily with double-locking. To avoid useless work
+    // when multiple threads attempt to initialize the same db at the same time, we trigger
+    // initialization manually before threads are in play.
+    git_odb* odb;
+    VERIFY(!git_repository_odb(&odb, repo)) << GitError();
+    git_odb_free(odb);
+
+    git_refdb* refdb;
+    VERIFY(!git_repository_refdb(&refdb, repo)) << GitError();
+    git_refdb_free(refdb);
+
+    elem = std::make_unique<Entry>(std::exchange(repo, nullptr), lim_);
+  }
+  elem->lru = lru_.insert({Clock::now(), x.first});
+  return elem.get();
+}
+
+void RepoCache::Free(Time cutoff) {
+  while (true) {
+    if (lru_.empty()) break;
+    auto it = lru_.begin();
+    if (it->first > cutoff) break;
+    Erase(it->second);
+  }
+}
+
+void RepoCache::Erase(Cache::iterator it) {
+  if (it == cache_.end()) return;
+  LOG(INFO) << "Closing repository: " << Print(it->first);
+  lru_.erase(it->second->lru);
+  cache_.erase(it);
+}
+
+}  // namespace gitstatus
diff --git a/src/repo_cache.h b/src/repo_cache.h
new file mode 100644
index 00000000..9d14ec06
--- /dev/null
+++ b/src/repo_cache.h
@@ -0,0 +1,60 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_REPO_CACHE_H_
+#define ROMKATV_GITSTATUS_REPO_CACHE_H_
+
+#include <map>
+#include <memory>
+#include <string>
+#include <unordered_map>
+#include <utility>
+
+#include <git2.h>
+
+#include "options.h"
+#include "repo.h"
+#include "time.h"
+
+namespace gitstatus {
+
+class RepoCache {
+ public:
+  explicit RepoCache(Limits lim) : lim_(std::move(lim)) {}
+  Repo* Open(const std::string& dir, bool from_dotgit);
+  void Free(Time cutoff);
+
+ private:
+  struct Entry;
+  using Cache = std::unordered_map<std::string, std::unique_ptr<Entry>>;
+  using LRU = std::multimap<Time, Cache::iterator>;
+
+  void Erase(Cache::iterator it);
+
+  Limits lim_;
+  Cache cache_;
+  LRU lru_;
+
+  struct Entry : Repo {
+    using Repo::Repo;
+    LRU::iterator lru;
+  };
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_REPO_CACHE_H_
diff --git a/src/request.cc b/src/request.cc
new file mode 100644
index 00000000..1a81bffb
--- /dev/null
+++ b/src/request.cc
@@ -0,0 +1,130 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "request.h"
+
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/select.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <cstdlib>
+#include <iostream>
+
+#include "check.h"
+#include "logging.h"
+#include "print.h"
+#include "serialization.h"
+
+namespace gitstatus {
+
+namespace {
+
+Request ParseRequest(const std::string& s) {
+  Request res;
+  auto begin = s.begin(), end = s.end(), sep = std::find(begin, end, kFieldSep);
+  VERIFY(sep != end) << "Malformed request: " << s;
+  res.id.assign(begin, sep);
+
+  begin = sep + 1;
+  if (*begin == ':') {
+    res.from_dotgit = true;
+    ++begin;
+  }
+  sep = std::find(begin, end, kFieldSep);
+  res.dir.assign(begin, sep);
+  if (sep == end) return res;
+
+  begin = sep + 1;
+  VERIFY(begin + 1 == end && (*begin == '0' || *begin == '1')) << "Malformed request: " << s;
+  res.diff = *begin == '0';
+  return res;
+}
+
+bool IsLockedFd(int fd) {
+  CHECK(fd >= 0);
+  struct flock flock = {};
+  flock.l_type = F_RDLCK;
+  flock.l_whence = SEEK_SET;
+  CHECK(fcntl(fd, F_GETLK, &flock) != -1) << Errno();
+  return flock.l_type != F_UNLCK;
+}
+
+}  // namespace
+
+std::ostream& operator<<(std::ostream& strm, const Request& req) {
+  strm << Print(req.id) << " for " << Print(req.dir);
+  if (req.from_dotgit) strm << " [from-dotgit]";
+  if (!req.diff) strm << " [no-diff]";
+  return strm;
+}
+
+RequestReader::RequestReader(int fd, int lock_fd, int parent_pid)
+    : fd_(fd), lock_fd_(lock_fd), parent_pid_(parent_pid) {
+  CHECK(fd != lock_fd);
+}
+
+bool RequestReader::ReadRequest(Request& req) {
+  auto eol = std::find(read_.begin(), read_.end(), kMsgSep);
+  if (eol != read_.end()) {
+    std::string msg(read_.begin(), eol);
+    read_.erase(read_.begin(), eol + 1);
+    req = ParseRequest(msg);
+    return true;
+  }
+
+  char buf[256];
+  while (true) {
+    fd_set fds;
+    FD_ZERO(&fds);
+    FD_SET(fd_, &fds);
+    struct timeval timeout = {.tv_sec = 1};
+
+    int n;
+    CHECK((n = select(fd_ + 1, &fds, NULL, NULL, &timeout)) >= 0) << Errno();
+    if (n == 0) {
+      if (lock_fd_ >= 0 && !IsLockedFd(lock_fd_)) {
+        LOG(INFO) << "Lock on fd " << lock_fd_ << " is gone. Exiting.";
+        std::exit(0);
+      }
+      if (parent_pid_ >= 0 && kill(parent_pid_, 0)) {
+        LOG(INFO) << "Unable to send signal 0 to " << parent_pid_ << ". Exiting.";
+        std::exit(0);
+      }
+      req = {};
+      return false;
+    }
+
+    CHECK((n = read(fd_, buf, sizeof(buf))) >= 0) << Errno();
+    if (n == 0) {
+      LOG(INFO) << "EOF. Exiting.";
+      std::exit(0);
+    }
+    read_.insert(read_.end(), buf, buf + n);
+    int eol = std::find(buf, buf + n, kMsgSep) - buf;
+    if (eol != n) {
+      std::string msg(read_.begin(), read_.end() - (n - eol));
+      read_.erase(read_.begin(), read_.begin() + msg.size() + 1);
+      req = ParseRequest(msg);
+      return true;
+    }
+  }
+}
+
+}  // namespace gitstatus
diff --git a/src/request.h b/src/request.h
new file mode 100644
index 00000000..2cc8baf9
--- /dev/null
+++ b/src/request.h
@@ -0,0 +1,50 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_REQUEST_H_
+#define ROMKATV_GITSTATUS_REQUEST_H_
+
+#include <deque>
+#include <ostream>
+#include <string>
+
+namespace gitstatus {
+
+struct Request {
+  std::string id;
+  std::string dir;
+  bool from_dotgit = false;
+  bool diff = true;
+};
+
+std::ostream& operator<<(std::ostream& strm, const Request& req);
+
+class RequestReader {
+ public:
+  RequestReader(int fd, int lock_fd, int parent_pid);
+  bool ReadRequest(Request& req);
+
+ private:
+  int fd_;
+  int lock_fd_;
+  int parent_pid_;
+  std::deque<char> read_;
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_REQUEST_H_
diff --git a/src/response.cc b/src/response.cc
new file mode 100644
index 00000000..eeb89c44
--- /dev/null
+++ b/src/response.cc
@@ -0,0 +1,73 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "response.h"
+
+#include <cctype>
+#include <cstring>
+#include <iostream>
+
+#include "check.h"
+#include "serialization.h"
+
+namespace gitstatus {
+
+namespace {
+
+constexpr char kUnreadable = '?';
+
+void SafePrint(std::ostream& strm, StringView s) {
+  for (size_t i = 0; i != s.len; ++i) {
+    char c = s.ptr[i];
+    strm << (c > 127 || std::isprint(c) ? c : kUnreadable);
+  }
+}
+
+}  // namespace
+
+ResponseWriter::ResponseWriter(std::string request_id) : request_id_(std::move(request_id)) {
+  SafePrint(strm_, request_id_);
+  Print(1);
+}
+
+ResponseWriter::~ResponseWriter() {
+  if (!done_) {
+    strm_.str("");
+    SafePrint(strm_, request_id_);
+    Print("0");
+    Dump("without git status");
+  }
+}
+
+void ResponseWriter::Print(ssize_t val) {
+  strm_ << kFieldSep;
+  strm_ << val;
+}
+
+void ResponseWriter::Print(StringView val) {
+  strm_ << kFieldSep;
+  SafePrint(strm_, val);
+}
+
+void ResponseWriter::Dump(const char* log) {
+  CHECK(!done_);
+  done_ = true;
+  LOG(INFO) << "Replying " << log;
+  std::cout << strm_.str() << kMsgSep << std::flush;
+}
+
+}  // namespace gitstatus
diff --git a/src/response.h b/src/response.h
new file mode 100644
index 00000000..12de765a
--- /dev/null
+++ b/src/response.h
@@ -0,0 +1,50 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_RESPONSE_H_
+#define ROMKATV_GITSTATUS_RESPONSE_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <sstream>
+#include <string>
+
+#include "string_view.h"
+
+namespace gitstatus {
+
+class ResponseWriter {
+ public:
+  ResponseWriter(std::string request_id);
+  ResponseWriter(ResponseWriter&&) = delete;
+  ~ResponseWriter();
+
+  void Print(ssize_t val);
+  void Print(StringView val);
+  void Print(const char* val) { Print(StringView(val)); }
+
+  void Dump(const char* log);
+
+ private:
+  bool done_ = false;
+  std::string request_id_;
+  std::ostringstream strm_;
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_RESPONSE_H_
diff --git a/src/scope_guard.h b/src/scope_guard.h
new file mode 100644
index 00000000..3a7aa01b
--- /dev/null
+++ b/src/scope_guard.h
@@ -0,0 +1,56 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_SCOPE_GUARD_H_
+#define ROMKATV_GITSTATUS_SCOPE_GUARD_H_
+
+#include <utility>
+
+#define ON_SCOPE_EXIT(capture...)                                     \
+  auto GITSTATUS_INTERNAL_CAT(_gitstatus_scope_guard_, __COUNTER__) = \
+      ::gitstatus::internal_scope_guard::ScopeGuardGenerator() = [capture]()
+
+#define GITSTATUS_INTERNAL_CAT_I(x, y) x##y
+#define GITSTATUS_INTERNAL_CAT(x, y) GITSTATUS_INTERNAL_CAT_I(x, y)
+
+namespace gitstatus {
+namespace internal_scope_guard {
+
+void Undefined();
+
+template <class F>
+class ScopeGuard {
+ public:
+  explicit ScopeGuard(F f) : f_(std::move(f)) {}
+  ~ScopeGuard() { std::move(f_)(); }
+  ScopeGuard(ScopeGuard&& other) : f_(std::move(other.f_)) { Undefined(); }
+
+ private:
+  F f_;
+};
+
+struct ScopeGuardGenerator {
+  template <class F>
+  ScopeGuard<F> operator=(F f) const {
+    return ScopeGuard<F>(std::move(f));
+  }
+};
+
+}  // namespace internal_scope_guard
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_SCOPE_GUARD_H_
diff --git a/src/serialization.h b/src/serialization.h
new file mode 100644
index 00000000..42b24098
--- /dev/null
+++ b/src/serialization.h
@@ -0,0 +1,28 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_SERIALIZATION_H_
+#define ROMKATV_GITSTATUS_SERIALIZATION_H_
+
+namespace gitstatus {
+
+constexpr char kFieldSep = 31;  // ascii 31 is unit separator
+constexpr char kMsgSep = 30;    // ascii 30 is record separator
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_SERIALIZATION_H_
diff --git a/src/stat.h b/src/stat.h
new file mode 100644
index 00000000..4f3195a7
--- /dev/null
+++ b/src/stat.h
@@ -0,0 +1,23 @@
+#ifndef ROMKATV_GITSTATUS_STAT_H_
+#define ROMKATV_GITSTATUS_STAT_H_
+
+#include <sys/stat.h>
+
+namespace gitstatus {
+
+inline const struct timespec& MTim(const struct stat& s) {
+#ifdef __APPLE__
+  return s.st_mtimespec;
+#else
+  return s.st_mtim;
+#endif
+}
+
+inline bool StatEq(const struct stat& x, const struct stat& y) {
+  return MTim(x).tv_sec == MTim(y).tv_sec && MTim(x).tv_nsec == MTim(y).tv_nsec &&
+         x.st_size == y.st_size && x.st_ino == y.st_ino && x.st_mode == y.st_mode;
+}
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_STAT_H_
diff --git a/src/string_cmp.h b/src/string_cmp.h
new file mode 100644
index 00000000..621c724c
--- /dev/null
+++ b/src/string_cmp.h
@@ -0,0 +1,151 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_STRING_CMP_H_
+#define ROMKATV_GITSTATUS_STRING_CMP_H_
+
+#include <string.h>  // because there is no std::strcasecmp in C++
+
+#include <algorithm>
+#include <cctype>
+#include <cstddef>
+#include <cstring>
+
+#include "string_view.h"
+
+namespace gitstatus {
+
+// WARNING: These routines assume no embedded null characters in StringView. Violations cause UB.
+
+template <int kCaseSensitive = -1>
+struct StrCmp;
+
+template <>
+struct StrCmp<0> {
+  int operator()(StringView x, StringView y) const {
+    size_t n = std::min(x.len, y.len);
+    int cmp = strncasecmp(x.ptr, y.ptr, n);
+    if (cmp) return cmp;
+    return static_cast<ssize_t>(x.len) - static_cast<ssize_t>(y.len);
+  }
+
+  int operator()(StringView x, const char* y) const {
+    for (const char *p = x.ptr, *e = p + x.len; p != e; ++p, ++y) {
+      if (int cmp = std::tolower(*p) - std::tolower(*y)) return cmp;
+    }
+    return 0 - *y;
+  }
+
+  int operator()(char x, char y) const { return std::tolower(x) - std::tolower(y); }
+  int operator()(const char* x, const char* y) const { return strcasecmp(x, y); }
+  int operator()(const char* x, StringView y) const { return -operator()(y, x); }
+};
+
+template <>
+struct StrCmp<1> {
+  int operator()(StringView x, StringView y) const {
+    size_t n = std::min(x.len, y.len);
+    int cmp = std::memcmp(x.ptr, y.ptr, n);
+    if (cmp) return cmp;
+    return static_cast<ssize_t>(x.len) - static_cast<ssize_t>(y.len);
+  }
+
+  int operator()(StringView x, const char* y) const {
+    for (const char *p = x.ptr, *e = p + x.len; p != e; ++p, ++y) {
+      if (int cmp = *p - *y) return cmp;
+    }
+    return 0 - *y;
+  }
+
+  int operator()(char x, char y) const { return x - y; }
+  int operator()(const char* x, const char* y) const { return std::strcmp(x, y); }
+  int operator()(const char* x, StringView y) const { return -operator()(y, x); }
+};
+
+template <>
+struct StrCmp<-1> {
+  explicit StrCmp(bool case_sensitive) : case_sensitive(case_sensitive) {}
+
+  template <class X, class Y>
+  int operator()(const X& x, const Y& y) const {
+    return case_sensitive ? StrCmp<1>()(x, y) : StrCmp<0>()(x, y);
+  }
+
+  bool case_sensitive;
+};
+
+template <int kCaseSensitive = -1>
+struct StrLt : private StrCmp<kCaseSensitive> {
+  using StrCmp<kCaseSensitive>::StrCmp;
+
+  template <class X, class Y>
+  bool operator()(const X& x, const Y& y) const {
+    return StrCmp<kCaseSensitive>::operator()(x, y) < 0;
+  }
+};
+
+template <int kCaseSensitive = -1>
+struct StrEq : private StrCmp<kCaseSensitive> {
+  using StrCmp<kCaseSensitive>::StrCmp;
+
+  template <class X, class Y>
+  bool operator()(const X& x, const Y& y) const {
+    return StrCmp<kCaseSensitive>::operator()(x, y) == 0;
+  }
+
+  bool operator()(const StringView& x, const StringView& y) const {
+    return x.len == y.len && StrCmp<kCaseSensitive>::operator()(x, y) == 0;
+  }
+};
+
+template <int kCaseSensitive = -1>
+struct Str {
+  static_assert(kCaseSensitive == 0 || kCaseSensitive == 1, "");
+
+  static const bool case_sensitive = kCaseSensitive;
+
+  StrCmp<kCaseSensitive> Cmp;
+  StrLt<kCaseSensitive> Lt;
+  StrEq<kCaseSensitive> Eq;
+};
+
+template <int kCaseSensitive>
+const bool Str<kCaseSensitive>::case_sensitive;
+
+template <>
+struct Str<-1> {
+  explicit Str(bool case_sensitive)
+      : case_sensitive(case_sensitive),
+        Cmp(case_sensitive),
+        Lt(case_sensitive),
+        Eq(case_sensitive) {}
+
+  bool case_sensitive;
+
+  StrCmp<-1> Cmp;
+  StrLt<-1> Lt;
+  StrEq<-1> Eq;
+};
+
+template <class Iter>
+void StrSort(Iter begin, Iter end, bool case_sensitive) {
+  case_sensitive ? std::sort(begin, end, StrLt<true>()) : std::sort(begin, end, StrLt<false>());
+}
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_STRING_CMP_H_
diff --git a/src/string_view.h b/src/string_view.h
new file mode 100644
index 00000000..e29414b5
--- /dev/null
+++ b/src/string_view.h
@@ -0,0 +1,77 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_STRING_VIEW_H_
+#define ROMKATV_GITSTATUS_STRING_VIEW_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <cstring>
+#include <ostream>
+#include <string>
+
+namespace gitstatus {
+
+// WARNING: StringView must not have embedded null characters. Violations cause UB.
+struct StringView {
+  StringView() : StringView("") {}
+
+  // Requires: !memchr(s.data(), 0, s.size()).
+  //
+  // WARNING: The existence of this requirement and the fact that this constructor is implicit
+  // means it's dangerous to have std::string instances with embedded null characters anywhere
+  // in the program. If you have an std::string `s` with embedded nulls, an innocent-looking
+  // `F(s)` might perform an implicit conversion to StringView and land you squarely in the
+  // Undefined Behavior land.
+  StringView(const std::string& s) : StringView(s.c_str(), s.size()) {}
+
+  // Requires: !memchr(ptr, 0, len).
+  StringView(const char* ptr, size_t len) : ptr(ptr), len(len) {}
+
+  // Requires: end >= begin && !memchr(begin, 0, end - begin).
+  StringView(const char* begin, const char* end) : StringView(begin, end - begin) {}
+
+  // Requires: strchr(s, 0) == s + N.
+  template <size_t N>
+  StringView(const char (&s)[N]) : StringView(s, N - 1) {
+    static_assert(N, "");
+  }
+
+  // Explicit because it's the only constructor that isn't O(1).
+  // Are you sure you don't already known the strings's length?
+  explicit StringView(const char* ptr) : StringView(ptr, ptr ? std::strlen(ptr) : 0) {}
+
+  bool StartsWith(StringView prefix) const {
+    return len >= prefix.len && !std::memcmp(ptr, prefix.ptr, prefix.len);
+  }
+
+  bool EndsWith(StringView suffix) const {
+    return len >= suffix.len && !std::memcmp(ptr + (len - suffix.len), suffix.ptr, suffix.len);
+  }
+
+  const char* ptr;
+  size_t len;
+};
+
+inline std::ostream& operator<<(std::ostream& strm, StringView s) {
+  if (s.ptr) strm.write(s.ptr, s.len);
+  return strm;
+}
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_STRING_VIEW_H_
diff --git a/src/strings.cc b/src/strings.cc
new file mode 100644
index 00000000..a68835d7
--- /dev/null
+++ b/src/strings.cc
@@ -0,0 +1,71 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include <cassert>
+
+#include "strings.h"
+
+namespace gitstatus {
+
+void CEscape(std::ostream& strm, const char* begin, const char* end) {
+  assert(!begin == !end);
+  if (!begin) return;
+  for (; begin != end; ++begin) {
+    const unsigned char c = *begin;
+    switch (c) {
+      case '\t':
+        strm << "\\t";
+        continue;
+      case '\n':
+        strm << "\\n";
+        continue;
+      case '\r':
+        strm << "\\r";
+        continue;
+      case '"':
+        strm << "\\\"";
+        continue;
+      case '\'':
+        strm << "\\'";
+        continue;
+      case '\\':
+        strm << "\\\\";
+        continue;
+    }
+    if (c > 31 && c < 127) {
+      strm << c;
+      continue;
+    }
+    strm << '\\';
+    strm << static_cast<char>('0' + ((c >> 6) & 7));
+    strm << static_cast<char>('0' + ((c >> 3) & 7));
+    strm << static_cast<char>('0' + ((c >> 0) & 7));
+  }
+}
+
+void Quote(std::ostream& strm, const char* begin, const char* end) {
+  assert(!begin == !end);
+  if (!begin) {
+    strm << "null";
+    return;
+  }
+  strm << '"';
+  CEscape(strm, begin, end);
+  strm << '"';
+}
+
+}  // namespace gitstatus
diff --git a/src/strings.h b/src/strings.h
new file mode 100644
index 00000000..a57cf20d
--- /dev/null
+++ b/src/strings.h
@@ -0,0 +1,37 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_STRINGS_H_
+#define ROMKATV_GITSTATUS_STRINGS_H_
+
+#include <ostream>
+
+namespace gitstatus {
+
+// If the pointers are null, prints nothing.
+//
+// Requires: !begin == !end.
+void CEscape(std::ostream& strm, const char* begin, const char* end);
+
+// If the pointers are null, prints null without quotes.
+//
+// Requires: !begin == !end.
+void Quote(std::ostream& strm, const char* begin, const char* end);
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_STRING_VIEW_H_
diff --git a/src/tag_db.cc b/src/tag_db.cc
new file mode 100644
index 00000000..0e440791
--- /dev/null
+++ b/src/tag_db.cc
@@ -0,0 +1,311 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "tag_db.h"
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <cstdlib>
+#include <cstring>
+#include <iterator>
+#include <utility>
+
+#include "check.h"
+#include "dir.h"
+#include "git.h"
+#include "print.h"
+#include "scope_guard.h"
+#include "stat.h"
+#include "string_cmp.h"
+#include "thread_pool.h"
+#include "timer.h"
+
+namespace gitstatus {
+
+namespace {
+
+using namespace std::string_literals;
+
+static constexpr char kTagPrefix[] = "refs/tags/";
+
+constexpr int8_t kUnhex[256] = {
+    0, 0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0,  // 0
+    0, 0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0,  // 1
+    0, 0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0,  // 2
+    0, 1,  2,  3,  4,  5,  6,  7, 8, 9, 0, 0, 0, 0, 0, 0,  // 3
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 4
+    0, 0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0,  // 5
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0   // 6
+};
+
+struct {
+  bool operator()(const Tag* x, const git_oid& y) const {
+    return std::memcmp(x->id.id, y.id, GIT_OID_RAWSZ) < 0;
+  }
+  bool operator()(const git_oid& x, const Tag* y) const {
+    return std::memcmp(x.id, y->id.id, GIT_OID_RAWSZ) < 0;
+  }
+  bool operator()(const Tag* x, const Tag* y) const {
+    return std::memcmp(x->id.id, y->id.id, GIT_OID_RAWSZ) < 0;
+  }
+} constexpr ById = {};
+
+struct {
+  bool operator()(const Tag* x, const char* y) const {
+    return std::strcmp(x->name, y) < 0;
+  }
+  bool operator()(const char* x, const Tag* y) const {
+    return std::strcmp(x, y->name) < 0;
+  }
+  bool operator()(const Tag* x, const Tag* y) const {
+    return std::strcmp(x->name, y->name) < 0;
+  }
+} constexpr ByName = {};
+
+void ParseOid(unsigned char* oid, const char* begin, const char* end) {
+  VERIFY(end >= begin + GIT_OID_HEXSZ);
+  for (size_t i = 0; i != GIT_OID_HEXSZ; i += 2) {
+    *oid++ = kUnhex[+begin[i]] << 4 | kUnhex[+begin[i + 1]];
+  }
+}
+
+const char* StripTag(const char* ref) {
+  for (size_t i = 0; i != sizeof(kTagPrefix) - 1; ++i) {
+    if (*ref++ != kTagPrefix[i]) return nullptr;
+  }
+  return ref;
+}
+
+git_refdb* RefDb(git_repository* repo) {
+  git_refdb* res;
+  VERIFY(!git_repository_refdb(&res, repo)) << GitError();
+  return res;
+}
+
+}  // namespace
+
+TagDb::TagDb(git_repository* repo)
+    : repo_(repo),
+      refdb_(RefDb(repo)),
+      pack_(&pack_arena_),
+      name2id_(&pack_arena_),
+      id2name_(&pack_arena_) {
+  CHECK(repo_ && refdb_);
+}
+
+TagDb::~TagDb() {
+  Wait();
+  git_refdb_free(refdb_);
+}
+
+std::string TagDb::TagForCommit(const git_oid& oid) {
+  ReadLooseTags();
+  UpdatePack();
+
+  std::string res;
+
+  std::string ref = "refs/tags/";
+  size_t prefix_len = ref.size();
+  for (const char* tag : loose_tags_) {
+    ref.resize(prefix_len);
+    ref += tag;
+    if (res < tag && TagHasTarget(ref.c_str(), &oid)) res = tag;
+  }
+
+  if ((std::unique_lock<std::mutex>(mutex_), id2name_dirty_)) {
+    for (auto it = name2id_.rbegin(); it != name2id_.rend(); ++it) {
+      if (!memcmp((*it)->id.id, oid.id, GIT_OID_RAWSZ) && !IsLooseTag((*it)->name)) {
+        if (res < (*it)->name) res = (*it)->name;
+        break;
+      }
+    }
+  } else {
+    auto r = std::equal_range(id2name_.begin(), id2name_.end(), oid, ById);
+    for (auto it = r.first; it != r.second; ++it) {
+      if (!IsLooseTag((*it)->name) && res < (*it)->name) res = (*it)->name;
+    }
+  }
+
+  return res;
+}
+
+void TagDb::ReadLooseTags() {
+  loose_tags_.clear();
+  loose_arena_.Reuse();
+
+  std::string dirname = git_repository_path(repo_) + "refs/tags"s;
+  int dir_fd = open(dirname.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+  if (dir_fd < 0) return;
+  ON_SCOPE_EXIT(&) { CHECK(!close(dir_fd)) << Errno(); };
+  (void)ListDir(dir_fd, loose_arena_, loose_tags_, /* precompose_unicode = */ false,
+                /* case_sensitive = */ true);
+}
+
+void TagDb::UpdatePack() {
+  auto Reset = [&] {
+    auto Wipe = [](auto& x) {
+      x.clear();
+      x.shrink_to_fit();
+    };
+    Wait();
+    Wipe(pack_);
+    Wipe(name2id_);
+    Wipe(id2name_);
+    pack_arena_.Reuse();
+    std::memset(&pack_stat_, 0, sizeof(pack_stat_));
+  };
+
+  std::string pack_path = git_repository_path(repo_) + "packed-refs"s;
+  struct stat st;
+  if (stat(pack_path.c_str(), &st)) {
+    Reset();
+    return;
+  }
+  if (StatEq(pack_stat_, st)) return;
+
+  Reset();
+
+  try {
+    while (true) {
+      LOG(INFO) << "Parsing " << Print(pack_path);
+      int fd = open(pack_path.c_str(), O_RDONLY | O_CLOEXEC);
+      VERIFY(fd >= 0);
+      ON_SCOPE_EXIT(&) { CHECK(!close(fd)) << Errno(); };
+      pack_.resize(st.st_size + 1);
+      ssize_t n = read(fd, &pack_[0], st.st_size + 1);
+      VERIFY(n >= 0) << Errno();
+      VERIFY(!fstat(fd, &pack_stat_)) << Errno();
+      if (!StatEq(st, pack_stat_)) {
+        st = pack_stat_;
+        continue;
+      }
+      VERIFY(n == st.st_size);
+      pack_.pop_back();
+      break;
+    }
+    ParsePack();
+  } catch (const Exception&) {
+    Reset();
+    throw;
+  }
+}
+
+void TagDb::ParsePack() {
+  char* p = &pack_[0];
+  char* e = p + pack_.size();
+
+  if (*p == '#') {
+    char* eol = std::strchr(p, '\n');
+    if (!eol) return;
+    *eol = 0;
+    if (!std::strstr(p, " fully-peeled") || !std::strstr(p, " sorted")) return;
+    p = eol + 1;
+  }
+
+  name2id_.reserve(pack_.size() / 128);
+  id2name_.reserve(pack_.size() / 128);
+
+  std::vector<Tag*> idx;
+  idx.reserve(pack_.size() / 128);
+
+  while (p != e) {
+    Tag* tag = pack_arena_.Allocate<Tag>();
+    ParseOid(tag->id.id, p, e);
+    p += GIT_OID_HEXSZ;
+    VERIFY(*p++ == ' ');
+    const char* ref = p;
+    VERIFY(p = std::strchr(p, '\n'));
+    p[p[-1] == '\r' ? -1 : 0] = 0;
+    ++p;
+    if (*p == '^') {
+      ParseOid(tag->id.id, p + 1, e);
+      p += GIT_OID_HEXSZ + 1;
+      if (p != e) {
+        VERIFY((p = std::strchr(p, '\n')));
+        ++p;
+      }
+    }
+    tag->name = StripTag(ref);
+    if (!tag->name) continue;
+    name2id_.push_back(tag);
+    id2name_.push_back(tag);
+  }
+
+  VERIFY(std::is_sorted(name2id_.begin(), name2id_.end(), ByName));
+
+  id2name_dirty_ = true;
+  GlobalThreadPool()->Schedule([this] {
+    std::sort(id2name_.begin(), id2name_.end(), ById);
+    std::unique_lock<std::mutex> lock(mutex_);
+    CHECK(id2name_dirty_);
+    id2name_dirty_ = false;
+    cv_.notify_one();
+  });
+}
+
+void TagDb::Wait() {
+  std::unique_lock<std::mutex> lock(mutex_);
+  while (id2name_dirty_) cv_.wait(lock);
+}
+
+bool TagDb::IsLooseTag(const char* name) const {
+  return std::binary_search(loose_tags_.begin(), loose_tags_.end(), name,
+                            [](const char* a, const char* b) { return std::strcmp(a, b) < 0; });
+}
+
+bool TagDb::TagHasTarget(const char* name, const git_oid* target) const {
+  static constexpr size_t kMaxDerefCount = 10;
+
+  git_reference* ref;
+  if (git_refdb_lookup(&ref, refdb_, name)) return false;
+  ON_SCOPE_EXIT(&) { git_reference_free(ref); };
+
+  for (int i = 0; i != kMaxDerefCount && git_reference_type(ref) == GIT_REFERENCE_SYMBOLIC; ++i) {
+    git_reference* dst;
+    const char* ref_name = git_reference_name(ref);
+    if (git_refdb_lookup(&dst, refdb_, ref_name)) {
+      const char* tag_name = StripTag(ref_name);
+      auto it = std::lower_bound(name2id_.begin(), name2id_.end(), tag_name, ByName);
+      return it != name2id_.end() && !strcmp((*it)->name, tag_name) && !IsLooseTag(tag_name) &&
+             git_oid_equal(&(*it)->id, target);
+    }
+    git_reference_free(ref);
+    ref = dst;
+  }
+
+  if (git_reference_type(ref) == GIT_REFERENCE_SYMBOLIC) return false;
+  const git_oid* oid = git_reference_target_peel(ref) ?: git_reference_target(ref);
+  if (git_oid_equal(oid, target)) return true;
+
+  for (int i = 0; i != kMaxDerefCount; ++i) {
+    git_tag* tag;
+    if (git_tag_lookup(&tag, repo_, oid)) return false;
+    ON_SCOPE_EXIT(&) { git_tag_free(tag); };
+    if (git_tag_target_type(tag) == GIT_OBJECT_COMMIT) {
+      return git_oid_equal(git_tag_target_id(tag), target);
+    }
+    oid = git_tag_target_id(tag);
+  }
+
+  return false;
+}
+
+}  // namespace gitstatus
diff --git a/src/tag_db.h b/src/tag_db.h
new file mode 100644
index 00000000..b5b14a48
--- /dev/null
+++ b/src/tag_db.h
@@ -0,0 +1,79 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_TAG_DB_H_
+#define ROMKATV_GITSTATUS_TAG_DB_H_
+
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <git2.h>
+
+#include <condition_variable>
+#include <cstring>
+#include <mutex>
+#include <string>
+#include <vector>
+
+#include "arena.h"
+
+namespace gitstatus {
+
+struct Tag {
+  const char* name;
+  git_oid id;
+};
+
+class TagDb {
+ public:
+  explicit TagDb(git_repository* repo);
+  TagDb(TagDb&&) = delete;
+  ~TagDb();
+
+  std::string TagForCommit(const git_oid& oid);
+
+ private:
+  void ReadLooseTags();
+  void UpdatePack();
+  void ParsePack();
+  void Wait();
+
+  bool IsLooseTag(const char* name) const;
+
+  bool TagHasTarget(const char* name, const git_oid* target) const;
+
+  git_repository* const repo_;
+  git_refdb* const refdb_;
+
+  Arena pack_arena_;
+  struct stat pack_stat_ = {};
+  WithArena<std::string> pack_;
+  WithArena<std::vector<const Tag*>> name2id_;
+  WithArena<std::vector<const Tag*>> id2name_;
+
+  Arena loose_arena_;
+  std::vector<char*> loose_tags_;
+
+  std::mutex mutex_;
+  std::condition_variable cv_;
+  bool id2name_dirty_ = false;
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_TAG_DB_H_
diff --git a/src/thread_pool.cc b/src/thread_pool.cc
new file mode 100644
index 00000000..b37eb203
--- /dev/null
+++ b/src/thread_pool.cc
@@ -0,0 +1,87 @@
+#include "thread_pool.h"
+
+#include <cassert>
+#include <utility>
+
+#include "check.h"
+#include "logging.h"
+
+namespace gitstatus {
+
+ThreadPool::ThreadPool(size_t num_threads) : num_inflight_(num_threads) {
+  for (size_t i = 0; i != num_threads; ++i) {
+    threads_.emplace_back([=]() { Loop(i + 1); });
+  }
+}
+
+ThreadPool::~ThreadPool() {
+  {
+    std::lock_guard<std::mutex> lock(mutex_);
+    exit_ = true;
+  }
+  cv_.notify_all();
+  sleeper_cv_.notify_one();
+  for (std::thread& t : threads_) t.join();
+}
+
+void ThreadPool::Schedule(Time t, std::function<void()> f) {
+  std::condition_variable* wake = nullptr;
+  {
+    std::unique_lock<std::mutex> lock(mutex_);
+    work_.push(Work{std::move(t), ++last_idx_, std::move(f)});
+    if (work_.top().idx == last_idx_) wake = have_sleeper_ ? &sleeper_cv_ : &cv_;
+  }
+  if (wake) wake->notify_one();
+}
+
+void ThreadPool::Loop(size_t tid) {
+  auto Next = [&]() -> std::function<void()> {
+    std::unique_lock<std::mutex> lock(mutex_);
+    --num_inflight_;
+    if (work_.empty() && num_inflight_ == 0) idle_cv_.notify_all();
+    while (true) {
+      if (exit_) return nullptr;
+      if (work_.empty()) {
+        cv_.wait(lock);
+        continue;
+      }
+      Time now = Clock::now();
+      const Work& top = work_.top();
+      if (top.t <= now) {
+        std::function<void()> res = std::move(top.f);
+        work_.pop();
+        ++num_inflight_;
+        bool notify = !work_.empty() && !have_sleeper_;
+        lock.unlock();
+        if (notify) cv_.notify_one();
+        return res;
+      }
+      if (have_sleeper_) {
+        cv_.wait(lock);
+        continue;
+      }
+      have_sleeper_ = true;
+      sleeper_cv_.wait_until(lock, top.t);
+      assert(have_sleeper_);
+      have_sleeper_ = false;
+    }
+  };
+  while (std::function<void()> f = Next()) f();
+}
+
+void ThreadPool::Wait() {
+  std::unique_lock<std::mutex> lock(mutex_);
+  idle_cv_.wait(lock, [&] { return work_.empty() && num_inflight_ == 0; });
+}
+
+static ThreadPool* g_thread_pool = nullptr;
+
+void InitGlobalThreadPool(size_t num_threads) {
+  CHECK(!g_thread_pool);
+  LOG(INFO) << "Spawning " << num_threads << " thread(s)";
+  g_thread_pool = new ThreadPool(num_threads);
+}
+
+ThreadPool* GlobalThreadPool() { return g_thread_pool; }
+
+}  // namespace gitstatus
diff --git a/src/thread_pool.h b/src/thread_pool.h
new file mode 100644
index 00000000..1e39b915
--- /dev/null
+++ b/src/thread_pool.h
@@ -0,0 +1,74 @@
+#ifndef ROMKATV_GITSTATUS_THREAD_POOL_H_
+#define ROMKATV_GITSTATUS_THREAD_POOL_H_
+
+#include <condition_variable>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <mutex>
+#include <queue>
+#include <thread>
+#include <tuple>
+#include <utility>
+
+#include "time.h"
+
+namespace gitstatus {
+
+class ThreadPool {
+ public:
+  explicit ThreadPool(size_t num_threads);
+  ThreadPool(ThreadPool&&) = delete;
+
+  // Waits for the currently running functions to finish.
+  // Does NOT wait for the queue of functions to drain.
+  // If you want the latter, call Wait() manually.
+  ~ThreadPool();
+
+  // Runs `f` on one of the threads at or after time `t`. Can be called
+  // from any thread. Can be called concurrently.
+  //
+  // Does not block.
+  void Schedule(Time t, std::function<void()> f);
+
+  void Schedule(std::function<void()> f) { Schedule(Clock::now(), std::move(f)); }
+
+  // Blocks until the work queue is empty and there are no currently
+  // running functions.
+  void Wait();
+
+  size_t num_threads() const { return threads_.size(); }
+
+ private:
+  struct Work {
+    bool operator<(const Work& w) const { return std::tie(w.t, w.idx) < std::tie(t, idx); }
+    Time t;
+    int64_t idx;
+    mutable std::function<void()> f;
+  };
+
+  void Loop(size_t tid);
+
+  int64_t last_idx_ = 0;
+  int64_t num_inflight_;
+  bool exit_ = false;
+  // Do we have a thread waiting on sleeper_cv_?
+  bool have_sleeper_ = false;
+  std::mutex mutex_;
+  // Any number of threads can wait on this condvar. Always without a timeout.
+  std::condition_variable cv_;
+  // At most one thread can wait on this condvar at a time. Always with a timeout.
+  std::condition_variable sleeper_cv_;
+  // Signalled when the work queue is empty and there is nothing inflight.
+  std::condition_variable idle_cv_;
+  std::priority_queue<Work> work_;
+  std::vector<std::thread> threads_;
+};
+
+void InitGlobalThreadPool(size_t num_threads);
+
+ThreadPool* GlobalThreadPool();
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_THREAD_POOL_H_
diff --git a/src/time.h b/src/time.h
new file mode 100644
index 00000000..cdd5fa27
--- /dev/null
+++ b/src/time.h
@@ -0,0 +1,14 @@
+#ifndef ROMKATV_GITSTATUS_TIME_H_
+#define ROMKATV_GITSTATUS_TIME_H_
+
+#include <chrono>
+
+namespace gitstatus {
+
+using Clock = std::chrono::steady_clock;
+using Time = Clock::time_point;
+using Duration = Clock::duration;
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_TIME_H_
diff --git a/src/timer.cc b/src/timer.cc
new file mode 100644
index 00000000..0e9f64e9
--- /dev/null
+++ b/src/timer.cc
@@ -0,0 +1,72 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#include "timer.h"
+
+#include <sys/resource.h>
+#include <sys/time.h>
+#include <time.h>
+
+#include <cmath>
+#include <limits>
+
+#include "check.h"
+#include "logging.h"
+
+namespace gitstatus {
+
+namespace {
+
+double CpuTimeMs() {
+  auto ToMs = [](const timeval& tv) { return 1e3 * tv.tv_sec + 1e-3 * tv.tv_usec; };
+  rusage usage = {};
+  CHECK(getrusage(RUSAGE_SELF, &usage) == 0) << Errno();
+  return ToMs(usage.ru_utime) + ToMs(usage.ru_stime);
+}
+
+double WallTimeMs() {
+  // An attempt to call clock_gettime on an ancient version of MacOS fails at runtime.
+  // It's possible to detect the presence of clock_gettime at runtime but I don't have
+  // an ancient MacOS to test the code. Hence this.
+#ifdef __APPLE__
+  return std::numeric_limits<double>::quiet_NaN();
+#else
+  struct timespec ts;
+  clock_gettime(CLOCK_MONOTONIC, &ts);
+  return 1e3 * ts.tv_sec + 1e-6 * ts.tv_nsec;
+#endif
+}
+
+}  // namespace
+
+void Timer::Start() {
+  cpu_ = CpuTimeMs();
+  wall_ = WallTimeMs();
+}
+
+void Timer::Report(const char* msg) {
+  double cpu = CpuTimeMs() - cpu_;
+  if (std::isnan(wall_)) {
+    LOG(INFO) << "Timing for: " << msg << ": " << cpu << "ms cpu";
+  } else {
+    double wall = WallTimeMs() - wall_;
+    LOG(INFO) << "Timing for: " << msg << ": " << cpu << "ms cpu, " << wall << "ms wall";
+  }
+  Start();
+}
+
+}  // namespace gitstatus
diff --git a/src/timer.h b/src/timer.h
new file mode 100644
index 00000000..51c557ca
--- /dev/null
+++ b/src/timer.h
@@ -0,0 +1,36 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_TIMER_H_
+#define ROMKATV_GITSTATUS_TIMER_H_
+
+namespace gitstatus {
+
+class Timer {
+ public:
+  Timer() { Start(); }
+  void Start();
+  void Report(const char* msg);
+
+ private:
+  double cpu_;
+  double wall_;
+};
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_TIMER_H_
diff --git a/src/tribool.h b/src/tribool.h
new file mode 100644
index 00000000..f06daf30
--- /dev/null
+++ b/src/tribool.h
@@ -0,0 +1,27 @@
+// Copyright 2019 Roman Perepelitsa.
+//
+// This file is part of GitStatus.
+//
+// GitStatus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// GitStatus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with GitStatus. If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef ROMKATV_GITSTATUS_TRIBOOL_H_
+#define ROMKATV_GITSTATUS_TRIBOOL_H_
+
+namespace gitstatus {
+
+enum class Tribool : int { kFalse = 0, kTrue = 1, kUnknown = -1 };
+
+}  // namespace gitstatus
+
+#endif  // ROMKATV_GITSTATUS_TRIBOOL_H_
-- 
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