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ThreadCachedArena.h
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ThreadCachedArena.h
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/*
* Copyright 2014 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef FOLLY_THREADCACHEDARENA_H_
#define FOLLY_THREADCACHEDARENA_H_
#include <utility>
#include <mutex>
#include <limits>
#include <boost/intrusive/slist.hpp>
#include "folly/Likely.h"
#include "folly/Arena.h"
#include "folly/ThreadLocal.h"
namespace folly {
/**
* Thread-caching arena: allocate memory which gets freed when the arena gets
* destroyed.
*
* The arena itself allocates memory using malloc() in blocks of
* at least minBlockSize bytes.
*
* For speed, each thread gets its own Arena (see Arena.h); when threads
* exit, the Arena gets merged into a "zombie" Arena, which will be deallocated
* when the ThreadCachedArena object is destroyed.
*/
class ThreadCachedArena {
public:
explicit ThreadCachedArena(
size_t minBlockSize = SysArena::kDefaultMinBlockSize);
void* allocate(size_t size) {
SysArena* arena = arena_.get();
if (UNLIKELY(!arena)) {
arena = allocateThreadLocalArena();
}
return arena->allocate(size);
}
void deallocate(void* p) {
// Deallocate? Never!
}
private:
ThreadCachedArena(const ThreadCachedArena&) = delete;
ThreadCachedArena(ThreadCachedArena&&) = delete;
ThreadCachedArena& operator=(const ThreadCachedArena&) = delete;
ThreadCachedArena& operator=(ThreadCachedArena&&) = delete;
SysArena* allocateThreadLocalArena();
// Zombify the blocks in arena, saving them for deallocation until
// the ThreadCachedArena is destroyed.
void zombify(SysArena&& arena);
size_t minBlockSize_;
SysArena zombies_; // allocated from threads that are now dead
std::mutex zombiesMutex_;
ThreadLocalPtr<SysArena> arena_; // per-thread arena
};
} // namespace folly
#endif /* FOLLY_THREADCACHEDARENA_H_ */