git / moonbite-core / src/leveldb/util/arena.cc · raw

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.// Use of this source code is governed by a BSD-style license that can be// found in the LICENSE file. See the AUTHORS file for names of contributors.#include "util/arena.h"namespace leveldb {static const int kBlockSize = 4096;Arena::Arena()    : alloc_ptr_(nullptr), alloc_bytes_remaining_(0), memory_usage_(0) {}Arena::~Arena() {  for (size_t i = 0; i < blocks_.size(); i++) {    delete[] blocks_[i];  }}char* Arena::AllocateFallback(size_t bytes) {  if (bytes > kBlockSize / 4) {    // Object is more than a quarter of our block size.  Allocate it separately    // to avoid wasting too much space in leftover bytes.    char* result = AllocateNewBlock(bytes);    return result;  }  // We waste the remaining space in the current block.  alloc_ptr_ = AllocateNewBlock(kBlockSize);  alloc_bytes_remaining_ = kBlockSize;  char* result = alloc_ptr_;  alloc_ptr_ += bytes;  alloc_bytes_remaining_ -= bytes;  return result;}char* Arena::AllocateAligned(size_t bytes) {  const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;  static_assert((align & (align - 1)) == 0,                "Pointer size should be a power of 2");  size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align - 1);  size_t slop = (current_mod == 0 ? 0 : align - current_mod);  size_t needed = bytes + slop;  char* result;  if (needed <= alloc_bytes_remaining_) {    result = alloc_ptr_ + slop;    alloc_ptr_ += needed;    alloc_bytes_remaining_ -= needed;  } else {    // AllocateFallback always returned aligned memory    result = AllocateFallback(bytes);  }  assert((reinterpret_cast<uintptr_t>(result) & (align - 1)) == 0);  return result;}char* Arena::AllocateNewBlock(size_t block_bytes) {  char* result = new char[block_bytes];  blocks_.push_back(result);  memory_usage_.fetch_add(block_bytes + sizeof(char*),                          std::memory_order_relaxed);  return result;}}  // namespace leveldb