C++ SpinLock、RecursiveSpinLock 基于原子CAS实现自旋锁（TASLock、TTASLock）

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本文使用内存屏障来 VolatileRead、VolatileWrite 保证读写重入自旋锁的当前线程ID（tid），如果不愿意采用内存屏障的方式来处理，人们可以选择使用原子变量读写来代替。

C++ 置R/W内存屏障：

            static inline void							MemoryBarrier() noexcept{std::atomic_thread_fence(std::memory_order_seq_cst);}

头文件：

#pragma once#include <ppp/stdafx.h>namespace ppp
{namespace threading{class SpinLock final{public:explicit SpinLock() noexcept;SpinLock(const SpinLock&) = delete;SpinLock(SpinLock&&) = delete;~SpinLock() noexcept(false);public:SpinLock&                   operator=(const SpinLock&) = delete;public:bool                        TryEnter() noexcept;bool                        TryEnter(int loop, int timeout) noexcept;void                        Enter() noexcept;void                        Leave();inline bool                 IsLockTaken() noexcept { return _.load(); }public:inline void                 lock() noexcept { Enter(); }inline void                 unlock() noexcept { Leave(); }public:std::atomic<bool>           _;};class RecursiveSpinLock final{public:explicit RecursiveSpinLock() noexcept;RecursiveSpinLock(const RecursiveSpinLock&) = delete;RecursiveSpinLock(RecursiveSpinLock&&) = delete;~RecursiveSpinLock() = default;public:RecursiveSpinLock&          operator=(const RecursiveSpinLock&) = delete;public:bool                        TryEnter() noexcept;bool                        TryEnter(int loop, int timeout) noexcept;void                        Enter() noexcept;void                        Leave();inline bool                 IsLockTaken() noexcept { return lockobj_.IsLockTaken(); }public:inline void                 lock() noexcept { Enter(); }inline void                 unlock() noexcept { Leave(); }public:SpinLock                    lockobj_;volatile int                tid_;std::atomic<int>            reentries_;};}
}

源文件：

#include <ppp/threading/SpinLock.h>
#include <ppp/threading/Thread.h>namespace ppp
{namespace threading{template <class LockObject>static constexpr bool Lock_TryEnter(LockObject&                                             lock, int                                                     loop,int                                                     timeout) noexcept{bool lockTaken = false;if (loop > -1){uint64_t last = GetTickCount();for (int i = 0; i < loop; i++){lockTaken = lock.TryEnter();if (lockTaken){break;}if (timeout > -1){uint64_t now = GetTickCount();int64_t diff = now - last;if (diff >= timeout){break;}}}}else{uint64_t last = GetTickCount();for (;;){lockTaken = lock.TryEnter();if (lockTaken){break;}if (timeout > -1){uint64_t now = GetTickCount();int64_t diff = now - last;if (diff >= timeout){break;}}}}return lockTaken;}template <class LockObject, class LockInternalObject, typename... TryEnterArguments>static constexpr bool RecursiveLock_TryEnter(LockObject&    lock, LockInternalObject&                                     lock_internal, volatile int*                                           tid,std::atomic<int>&                                       reentries, TryEnterArguments&&...                                  arguments){int n = ++reentries;assert(n > 0);int current_tid = std::hash<std::thread::id>{}(std::this_thread::get_id());if (n == 1){bool lockTaken = lock_internal.TryEnter(std::forward<TryEnterArguments>(arguments)...);if (!lockTaken){reentries--;return false;}Thread::MemoryBarrier();*tid = current_tid;Thread::MemoryBarrier();}else{Thread::MemoryBarrier();int lockTaken_tid = *tid;Thread::MemoryBarrier();if (lockTaken_tid == current_tid){lock.Leave();return false;}}return true;}SpinLock::SpinLock() noexcept: _(false){}SpinLock::~SpinLock() noexcept(false){bool lockTaken = IsLockTaken();if (lockTaken){throw std::runtime_error("fail to release the atomic lock.");}}void SpinLock::Enter() noexcept{for (;;) {bool lockTaken = TryEnter();if (lockTaken){break;}}}bool SpinLock::TryEnter(int loop, int timeout) noexcept{return Lock_TryEnter(*this, loop, timeout);}bool SpinLock::TryEnter() noexcept{bool expected = false;return _.compare_exchange_strong(expected, true, std::memory_order_acquire);}void SpinLock::Leave(){bool expected = true;if (!_.compare_exchange_strong(expected, false, std::memory_order_release)){throw std::runtime_error("failed to acquire the atomic lock.");}}RecursiveSpinLock::RecursiveSpinLock() noexcept: lockobj_(), tid_(0), reentries_(0){}bool RecursiveSpinLock::TryEnter() noexcept{return RecursiveLock_TryEnter(*this, lockobj_, &tid_, reentries_);}bool RecursiveSpinLock::TryEnter(int loop, int timeout) noexcept{return RecursiveLock_TryEnter(*this, lockobj_, &tid_, reentries_, loop, timeout);}void RecursiveSpinLock::Enter() noexcept{for (;;){bool lockTaken = TryEnter();if (lockTaken){break;}}}void RecursiveSpinLock::Leave() {int n = --reentries_;assert(n >= 0);if (n == 0){lockobj_.Leave();}}}
}

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