SpinLock.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "HAL/PlatformProcess.h"
#include <atomic>
 
namespace UE
{
    // A mutex that doesn't put the thread into a WAIT state but instead repeatedly tries to aquire the lock.
    // WARNING: Should be used only for very short locks
    // Use with `TScopeLock`
    class FSpinLock
    {
    public:
        UE_NONCOPYABLE(FSpinLock);
 
        FSpinLock() = default;
 
        void Lock()
        {
            while (true)
            {
                if (!bFlag.exchange(true, std::memory_order_acquire))
                {
                    break;
                }
 
                while (bFlag.load(std::memory_order_relaxed))
                {
                    FPlatformProcess::Yield();
                }
            }
        }
 
        bool TryLock()
        {
            return !bFlag.exchange(true, std::memory_order_acquire);
        }
 
        void Unlock()
        {
            bFlag.store(false, std::memory_order_release);
        }
 
    private:
        std::atomic<bool> bFlag{ false };
    };
}