作者: 谢瑞阳 10225101483 徐翔宇 10225101535
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// 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.
#ifndef STORAGE_LEVELDB_UTIL_ARENA_H_
#define STORAGE_LEVELDB_UTIL_ARENA_H_
#include <atomic>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <vector>
namespace leveldb {
class Arena {
public:
Arena();
~Arena();
// Return a pointer to a newly allocated memory block of "bytes" bytes.
char* Allocate(size_t bytes);
// Allocate memory with the normal alignment guarantees provided by malloc.
char* AllocateAligned(size_t bytes);
// Returns an estimate of the total memory usage of data allocated
// by the arena.
size_t MemoryUsage() const {
return memory_usage_.load(std::memory_order_relaxed);
}
private:
char* AllocateFallback(size_t bytes);
char* AllocateNewBlock(size_t block_bytes);
// Allocation state
char* alloc_ptr_;
size_t alloc_bytes_remaining_;
// Array of new[] allocated memory blocks
std::vector<char*> blocks_;
// Total memory usage of the arena.
//
// TODO(costan): This member is accessed via atomics, but the others are
// accessed without any locking. Is this OK?
std::atomic<size_t> memory_usage_;
// No copying allowed
Arena(const Arena&);
void operator=(const Arena&);
};
inline char* Arena::Allocate(size_t bytes) {
// The semantics of what to return are a bit messy if we allow
// 0-byte allocations, so we disallow them here (we don't need
// them for our internal use).
assert(bytes > 0);
if (bytes <= alloc_bytes_remaining_) {
char* result = alloc_ptr_;
alloc_ptr_ += bytes;
alloc_bytes_remaining_ -= bytes;
return result;
}
return AllocateFallback(bytes);
}
} // namespace leveldb
#endif // STORAGE_LEVELDB_UTIL_ARENA_H_