// 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_
