// 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