mirror of https://github.com/facebook/rocksdb.git
85 lines
2.5 KiB
C++
85 lines
2.5 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// 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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// ArenaImpl is an implementation of Arena class. For a request of small size,
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// it allocates a block with pre-defined block size. For a request of big
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// size, it uses malloc to directly get the requested size.
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#pragma once
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#include <cstddef>
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#include <vector>
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#include <assert.h>
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#include <stdint.h>
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#include "rocksdb/arena.h"
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namespace rocksdb {
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class ArenaImpl : public Arena {
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public:
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explicit ArenaImpl(size_t block_size = kMinBlockSize);
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virtual ~ArenaImpl();
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virtual char* Allocate(size_t bytes);
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virtual char* AllocateAligned(size_t bytes);
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// Returns an estimate of the total memory usage of data allocated
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// by the arena (including space allocated but not yet used for user
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// allocations).
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//
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// TODO: Do we need to exclude space allocated but not used?
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virtual const size_t ApproximateMemoryUsage() {
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return blocks_memory_ + blocks_.capacity() * sizeof(char*);
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}
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virtual const size_t MemoryAllocatedBytes() {
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return blocks_memory_;
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}
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private:
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char* AllocateFallback(size_t bytes);
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char* AllocateNewBlock(size_t block_bytes);
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static const size_t kMinBlockSize = 4096;
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static const size_t kMaxBlockSize = 2 << 30;
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// Number of bytes allocated in one block
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size_t block_size_;
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// Allocation state
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char* alloc_ptr_;
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size_t alloc_bytes_remaining_;
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// Array of new[] allocated memory blocks
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std::vector<char*> blocks_;
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// Bytes of memory in blocks allocated so far
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size_t blocks_memory_;
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// No copying allowed
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ArenaImpl(const ArenaImpl&);
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void operator=(const ArenaImpl&);
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};
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inline char* ArenaImpl::Allocate(size_t bytes) {
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// The semantics of what to return are a bit messy if we allow
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// 0-byte allocations, so we disallow them here (we don't need
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// them for our internal use).
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assert(bytes > 0);
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if (bytes <= alloc_bytes_remaining_) {
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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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return AllocateFallback(bytes);
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}
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} // namespace rocksdb
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