folly/folly/memory/Arena.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once
#define FOLLY_ARENA_H_

#include <cassert>
#include <limits>
#include <stdexcept>
#include <utility>

#include <boost/intrusive/slist.hpp>

#include <folly/Conv.h>
#include <folly/Likely.h>
#include <folly/Memory.h>
#include <folly/lang/Align.h>
#include <folly/lang/CheckedMath.h>
#include <folly/lang/Exception.h>
#include <folly/memory/Malloc.h>

namespace folly {

/**
 * Simple arena: allocate memory which gets freed when the arena gets
 * destroyed.
 *
 * The arena itself allocates memory using a custom allocator which conforms
 * to the C++ concept Allocator.
 *
 *   http://en.cppreference.com/w/cpp/concept/Allocator
 *
 * You may also specialize ArenaAllocatorTraits for your allocator type to
 * provide:
 *
 *   size_t goodSize(const Allocator& alloc, size_t size) const;
 *      Return a size (>= the provided size) that is considered "good" for your
 *      allocator (for example, if your allocator allocates memory in 4MB
 *      chunks, size should be rounded up to 4MB).  The provided value is
 *      guaranteed to be rounded up to a multiple of the maximum alignment
 *      required on your system; the returned value must be also.
 *
 * An implementation that uses malloc() / free() is defined below, see SysArena.
 */
template <class Alloc>
struct ArenaAllocatorTraits;
template <class Alloc>
class Arena { … };

AllocatorHasTrivialDeallocate<Arena<Alloc>>;

/**
 * By default, don't pad the given size.
 */
template <class Alloc>
struct ArenaAllocatorTraits { … };

template <>
struct ArenaAllocatorTraits<SysAllocator<char>> { … };

/**
 * Arena that uses the system allocator (malloc / free)
 */
class SysArena : public Arena<SysAllocator<char>> { … };

template <>
struct AllocatorHasTrivialDeallocate<SysArena> : std::true_type { … };

ArenaAllocator;

SysArenaAllocator;

FallbackArenaAllocator;

FallbackSysArenaAllocator;

} // namespace folly

#include <folly/memory/Arena-inl.h>