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