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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
#ifndef MOZILLA_GFX_ITERABLEARENA_H_
#define MOZILLA_GFX_ITERABLEARENA_H_
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <utility>
#include <vector>
#include "mozilla/Assertions.h"
#include "mozilla/gfx/Logging.h"
namespace mozilla {
namespace gfx {
/// A simple pool allocator for plain data structures.
///
/// Beware that the pool will not attempt to run the destructors. It is the
/// responsibility of the user of this class to either use objects with no
/// destructor or to manually call the allocated objects destructors.
/// If the pool is growable, its allocated objects must be safely moveable in
/// in memory (through memcpy).
class IterableArena {
protected:
struct Header {
size_t mBlocSize;
};
public:
enum ArenaType { FIXED_SIZE, GROWABLE };
IterableArena(ArenaType aType, size_t aStorageSize)
: mSize(aStorageSize), mCursor(0), mIsGrowable(aType == GROWABLE) {
if (mSize == 0) {
mSize = 128;
}
mStorage = (uint8_t*)malloc(mSize);
if (mStorage == nullptr) {
gfxCriticalError() << "Not enough Memory allocate a memory pool of size "
<< aStorageSize;
MOZ_CRASH("GFX: Out of memory IterableArena");
}
}
~IterableArena() { free(mStorage); }
/// Constructs a new item in the pool and returns a positive offset in case of
/// success.
///
/// The offset never changes even if the storage is reallocated, so users
/// of this class should prefer storing offsets rather than direct pointers
/// to the allocated objects.
/// Alloc can cause the storage to be reallocated if the pool was initialized
/// with IterableArena::GROWABLE.
/// If for any reason the pool fails to allocate enough space for the new item
/// Alloc returns a negative offset and the object's constructor is not
/// called.
template <typename T, typename... Args>
ptrdiff_t Alloc(Args&&... aArgs) {
void* storage = nullptr;
auto offset = AllocRaw(sizeof(T), &storage);
if (offset < 0) {
return offset;
}
new (storage) T(std::forward<Args>(aArgs)...);
return offset;
}
ptrdiff_t AllocRaw(size_t aSize, void** aOutPtr = nullptr) {
const size_t blocSize = AlignedSize(sizeof(Header) + aSize);
if (AlignedSize(mCursor + blocSize) > mSize) {
if (!mIsGrowable) {
return -1;
}
size_t newSize = mSize * 2;
while (AlignedSize(mCursor + blocSize) > newSize) {
newSize *= 2;
}
uint8_t* newStorage = (uint8_t*)realloc(mStorage, newSize);
if (!newStorage) {
gfxCriticalError()
<< "Not enough Memory to grow the memory pool, size: " << newSize;
return -1;
}
mStorage = newStorage;
mSize = newSize;
}
ptrdiff_t offset = mCursor;
GetHeader(offset)->mBlocSize = blocSize;
mCursor += blocSize;
if (aOutPtr) {
*aOutPtr = GetStorage(offset);
}
return offset;
}
/// Get access to an allocated item at a given offset (only use offsets
/// returned by Alloc or AllocRaw).
///
/// If the pool is growable, the returned pointer is only valid temporarily.
/// The underlying storage can be reallocated in Alloc or AllocRaw, so do not
/// keep these pointers around and store the offset instead.
void* GetStorage(ptrdiff_t offset = 0) {
MOZ_ASSERT(offset >= 0);
MOZ_ASSERT(offset < mCursor);
return offset >= 0 ? mStorage + offset + sizeof(Header) : nullptr;
}
/// Clears the storage without running any destructor and without deallocating
/// it.
void Clear() { mCursor = 0; }
/// Iterate over the elements allocated in this pool.
///
/// Takes a lambda or function object accepting a void* as parameter.
template <typename Func>
void ForEach(Func cb) {
Iterator it;
while (void* ptr = it.Next(this)) {
cb(ptr);
}
}
/// A simple iterator over an arena.
class Iterator {
public:
Iterator() : mCursor(0) {}
void* Next(IterableArena* aArena) {
if (mCursor >= aArena->mCursor) {
return nullptr;
}
void* result = aArena->GetStorage(mCursor);
const size_t blocSize = aArena->GetHeader(mCursor)->mBlocSize;
MOZ_ASSERT(blocSize != 0);
mCursor += blocSize;
return result;
}
private:
ptrdiff_t mCursor;
};
protected:
Header* GetHeader(ptrdiff_t offset) { return (Header*)(mStorage + offset); }
size_t AlignedSize(size_t aSize) const {
const size_t alignment = sizeof(uintptr_t);
return aSize + (alignment - (aSize % alignment)) % alignment;
}
uint8_t* mStorage;
uint32_t mSize;
ptrdiff_t mCursor;
bool mIsGrowable;
friend class Iterator;
};
} // namespace gfx
} // namespace mozilla
#endif