84 lines
2.2 KiB
C++
84 lines
2.2 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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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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/*
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* N.B. You most likely do _not_ want to use SpinLock or any other
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* kind of spinlock. Use std::mutex instead.
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*
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* In short, spinlocks in preemptive multi-tasking operating systems
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* have serious problems and fast mutexes like std::mutex are almost
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* certainly the better choice, because letting the OS scheduler put a
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* thread to sleep is better for system responsiveness and throughput
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* than wasting a timeslice repeatedly querying a lock held by a
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* thread that's blocked, and you can't prevent userspace
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* programs blocking.
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*
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* Spinlocks in an operating system kernel make much more sense than
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* they do in userspace.
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*/
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#pragma once
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#include <type_traits>
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#include <folly/Portability.h>
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#include <folly/synchronization/SmallLocks.h>
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namespace folly {
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class SpinLock {
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public:
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FOLLY_ALWAYS_INLINE SpinLock() noexcept {
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lock_.init();
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}
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FOLLY_ALWAYS_INLINE void lock() const noexcept {
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lock_.lock();
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}
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FOLLY_ALWAYS_INLINE void unlock() const noexcept {
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lock_.unlock();
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}
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FOLLY_ALWAYS_INLINE bool try_lock() const noexcept {
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return lock_.try_lock();
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}
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private:
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mutable folly::MicroSpinLock lock_;
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};
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template <typename LOCK>
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class SpinLockGuardImpl {
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public:
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FOLLY_ALWAYS_INLINE explicit SpinLockGuardImpl(LOCK& lock) noexcept(
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noexcept(lock.lock()))
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: lock_(lock) {
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lock_.lock();
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}
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SpinLockGuardImpl(const SpinLockGuardImpl&) = delete;
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SpinLockGuardImpl& operator=(const SpinLockGuardImpl&) = delete;
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FOLLY_ALWAYS_INLINE ~SpinLockGuardImpl() {
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lock_.unlock();
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}
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private:
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LOCK& lock_;
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};
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typedef SpinLockGuardImpl<SpinLock> SpinLockGuard;
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} // namespace folly
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