Arena-inl.h

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/*
 * Copyright 2012-present Facebook, Inc.
 *
 * 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.
 */

#ifndef FOLLY_ARENA_H_
#error This file may only be included from Arena.h
#endif

// Implementation of Arena.h functions

namespace folly {

template <class Alloc>
std::pair<typename Arena<Alloc>::Block*, size_t>
Arena<Alloc>::Block::allocate(Alloc& alloc, size_t size, bool allowSlack) {
  size_t allocSize = sizeof(Block) + size;
  if (allowSlack) {
    allocSize = ArenaAllocatorTraits<Alloc>::goodSize(alloc, allocSize);
  }

  void* mem = std::allocator_traits<Alloc>::allocate(alloc, allocSize);
  return std::make_pair(new (mem) Block(), allocSize - sizeof(Block));
}

template <class Alloc>
void Arena<Alloc>::Block::deallocate(Alloc& alloc) {
  this->~Block();
  std::allocator_traits<Alloc>::deallocate(alloc, this, 1);
}

template <class Alloc>
void* Arena<Alloc>::allocateSlow(size_t size) {
  std::pair<Block*, size_t> p;
  char* start;

  size_t allocSize = std::max(size, minBlockSize()) + sizeof(Block);
  if (sizeLimit_ != kNoSizeLimit &&
      allocSize > sizeLimit_ - totalAllocatedSize_) {
    throw_exception(std::bad_alloc());
  }

  if (size > minBlockSize()) {
    // Allocate a large block for this chunk only, put it at the back of the
    // list so it doesn't get used for small allocations; don't change ptr_
    // and end_, let them point into a normal block (or none, if they're
    // null)
    p = Block::allocate(alloc(), size, false);
    start = p.first->start();
    blocks_.push_back(*p.first);
  } else {
    // Allocate a normal sized block and carve out size bytes from it
    p = Block::allocate(alloc(), minBlockSize(), true);
    start = p.first->start();
    blocks_.push_front(*p.first);
    ptr_ = start + size;
    end_ = start + p.second;
  }

  assert(p.second >= size);
  totalAllocatedSize_ += p.second + sizeof(Block);
  return start;
}

template <class Alloc>
void Arena<Alloc>::merge(Arena<Alloc>&& other) {
  blocks_.splice_after(blocks_.before_begin(), other.blocks_);
  other.blocks_.clear();
  other.ptr_ = other.end_ = nullptr;
  totalAllocatedSize_ += other.totalAllocatedSize_;
  other.totalAllocatedSize_ = 0;
}

template <class Alloc>
Arena<Alloc>::~Arena() {
  auto disposer = [this](Block* b) { b->deallocate(this->alloc()); };
  while (!blocks_.empty()) {
    blocks_.pop_front_and_dispose(disposer);
  }
}

} // namespace folly