YiSpinLock.h

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// © You i Labs Inc. 2000-2017. All rights reserved.
#ifndef _YI_SPINLOCK_H_
#define _YI_SPINLOCK_H_

#include "framework/YiPredef.h"

#include <atomic>
#include <thread>

#ifndef YI_SPINLOCK_ATTEMPTS_BEFORE_YIELD
#define YI_SPINLOCK_ATTEMPTS_BEFORE_YIELD 10000
#endif

class CYISpinLock
{
public:
    CYISpinLock();

    bool Lock();

    bool TryLock();

    bool Unlock();

private:
#if defined(_MSC_VER) && _MSC_VER <= 1800 // VS2013 or older. Non-static data member initializer is not implemented, and will be done in the constructor instead.
    std::atomic_flag m_lock;
#else
    std::atomic_flag m_lock = ATOMIC_FLAG_INIT;
#endif

    YI_DISALLOW_COPY_AND_ASSIGN(CYISpinLock)
};

inline CYISpinLock::CYISpinLock()
{
#if defined(_MSC_VER) && _MSC_VER <= 1800 // VS2013 or older. GCC and Clang atomic_flag implementations do not allow operator=.
    m_lock.clear();
#endif
}

inline bool CYISpinLock::Lock()
{
    while (true)
    {
        for (int32_t i = 0; i < YI_SPINLOCK_ATTEMPTS_BEFORE_YIELD; ++i)
        {
            if (!m_lock.test_and_set(std::memory_order_acquire))
            {
                return true; // Lock acquired.
            }
        }
        std::this_thread::yield();
    }
}

inline bool CYISpinLock::TryLock()
{
    return !m_lock.test_and_set(std::memory_order_acquire);
}

inline bool CYISpinLock::Unlock()
{
    m_lock.clear(std::memory_order_release);
    return true;
}

#endif /* _YI_SPINLOCK_H_ */