util/include/chre/util/memory_pool_impl.h

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * 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 CHRE_UTIL_MEMORY_POOL_IMPL_H_
#define CHRE_UTIL_MEMORY_POOL_IMPL_H_

#include "chre/util/memory_pool.h"

#include <utility>

namespace chre {

template<typename ElementType, size_t kSize>
MemoryPool<ElementType, kSize>::MemoryPool() {
  // Initialize the free block list. The initial condition is such that each
  // block points to the next as being empty. The mFreeBlockCount is used to
  // ensure that we never allocate out of bounds so we don't need to worry about
  // the last block referring to one that is non-existent.
  for (size_t i = 0; i < kSize; i++) {
    mBlocks.emplace_back(i + 1);
  }
}

template<typename ElementType, size_t kSize>
template<typename... Args>
ElementType *MemoryPool<ElementType, kSize>::allocate(Args&&... args) {
  if (mFreeBlockCount == 0) {
    return nullptr;
  }

  size_t blockIndex = mNextFreeBlockIndex;
  mNextFreeBlockIndex = mBlocks[blockIndex].mNextFreeBlockIndex;
  mFreeBlockCount--;

  return new (&mBlocks[blockIndex].mElement)
      ElementType(std::forward<Args>(args)...);
}

template<typename ElementType, size_t kSize>
void MemoryPool<ElementType, kSize>::deallocate(ElementType *element) {
  uintptr_t elementAddress = reinterpret_cast<uintptr_t>(element);
  uintptr_t baseAddress = reinterpret_cast<uintptr_t>(&mBlocks[0].mElement);
  size_t blockIndex = (elementAddress - baseAddress) / sizeof(MemoryPoolBlock);

  mBlocks[blockIndex].mElement.~ElementType();
  mBlocks[blockIndex].mNextFreeBlockIndex = mNextFreeBlockIndex;
  mNextFreeBlockIndex = blockIndex;
  mFreeBlockCount++;
}

template<typename ElementType, size_t kSize>
MemoryPool<ElementType, kSize>::MemoryPoolBlock::MemoryPoolBlock(
    size_t nextFreeBlockIndex) : mNextFreeBlockIndex(nextFreeBlockIndex) {}

}  // namespace chre

#endif  // CHRE_UTIL_MEMORY_POOL_IMPL_H_