text: /*
   * Copyright 2016 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 = alloc.allocate(allocSize);
    return std::make_pair(new (mem) Block(), allocSize - sizeof(Block));
  }
  
  template <class Alloc>
  void Arena<Alloc>::Block::deallocate(Alloc& alloc) {
    this->~Block();
    alloc.deallocate(this);
  }
  
  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 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
  