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71 行
1.9 KiB
71 行
1.9 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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#ifndef STORAGE_LEVELDB_UTIL_ARENA_H_
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#define STORAGE_LEVELDB_UTIL_ARENA_H_
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#include <atomic>
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
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#include <vector>
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namespace leveldb {
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class Arena {
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public:
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Arena();
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Arena(const Arena&) = delete;
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Arena& operator=(const Arena&) = delete;
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~Arena();
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// Return a pointer to a newly allocated memory block of "bytes" bytes.
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char* Allocate(size_t bytes);
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// Allocate memory with the normal alignment guarantees provided by malloc.
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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.
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size_t MemoryUsage() const {
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return memory_usage_.load(std::memory_order_relaxed);
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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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// 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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// Total memory usage of the arena.
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//
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// TODO(costan): This member is accessed via atomics, but the others are
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// accessed without any locking. Is this OK?
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std::atomic<size_t> memory_usage_;
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};
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inline char* Arena::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 leveldb
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#endif // STORAGE_LEVELDB_UTIL_ARENA_H_
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