| // 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" |
| #include <assert.h> |
| |
| namespace leveldb { |
| |
| static const int kBlockSize = 4096; |
| |
| Arena::Arena() { |
| blocks_memory_ = 0; |
| alloc_ptr_ = NULL; // First allocation will allocate a block |
| alloc_bytes_remaining_ = 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; |
| 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_memory_ += block_bytes; |
| blocks_.push_back(result); |
| return result; |
| } |
| |
| } // namespace leveldb |