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88 lines
2.4 KiB
C++
88 lines
2.4 KiB
C++
/*
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* Copyright 2016 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <type_traits>
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#include <folly/Arena.h>
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#include <folly/Likely.h>
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#include <folly/Synchronized.h>
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#include <folly/ThreadLocal.h>
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namespace folly {
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/**
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* Thread-caching arena: allocate memory which gets freed when the arena gets
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* destroyed.
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*
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* The arena itself allocates memory using malloc() in blocks of
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* at least minBlockSize bytes.
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*
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* For speed, each thread gets its own Arena (see Arena.h); when threads
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* exit, the Arena gets merged into a "zombie" Arena, which will be deallocated
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* when the ThreadCachedArena object is destroyed.
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*/
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class ThreadCachedArena {
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public:
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explicit ThreadCachedArena(
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size_t minBlockSize = SysArena::kDefaultMinBlockSize,
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size_t maxAlign = SysArena::kDefaultMaxAlign);
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void* allocate(size_t size) {
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SysArena* arena = arena_.get();
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if (UNLIKELY(!arena)) {
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arena = allocateThreadLocalArena();
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}
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return arena->allocate(size);
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}
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void deallocate(void* /* p */) {
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// Deallocate? Never!
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}
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// Gets the total memory used by the arena
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size_t totalSize() const;
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private:
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struct ThreadLocalPtrTag {};
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ThreadCachedArena(const ThreadCachedArena&) = delete;
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ThreadCachedArena(ThreadCachedArena&&) = delete;
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ThreadCachedArena& operator=(const ThreadCachedArena&) = delete;
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ThreadCachedArena& operator=(ThreadCachedArena&&) = delete;
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SysArena* allocateThreadLocalArena();
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// Zombify the blocks in arena, saving them for deallocation until
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// the ThreadCachedArena is destroyed.
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void zombify(SysArena&& arena);
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const size_t minBlockSize_;
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const size_t maxAlign_;
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ThreadLocalPtr<SysArena, ThreadLocalPtrTag> arena_; // Per-thread arena.
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// Allocations from threads that are now dead.
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Synchronized<SysArena> zombies_;
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};
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template <>
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struct IsArenaAllocator<ThreadCachedArena> : std::true_type { };
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} // namespace folly
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