RecursiveMutex.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include <atomic>
 
#define UE_API CORE_API
 
namespace UE
{
 
class FRecursiveMutex final
{
public:
    constexpr FRecursiveMutex() = default;
 
    FRecursiveMutex(const FRecursiveMutex&) = delete;
    FRecursiveMutex& operator=(const FRecursiveMutex&) = delete;
 
    [[nodiscard]] inline bool IsLocked() const
    {
        return !!(State.load(std::memory_order_relaxed) & LockCountMask);
    }
 
    [[nodiscard]] UE_API bool TryLock();
    UE_API void Lock();
    UE_API void Unlock();
 
private:
    void LockSlow(uint32 CurrentState, uint32 CurrentThreadId);
    void WakeWaitingThread();
 
    static constexpr uint32 MayHaveWaitingLockFlag = 1 << 0;
    static constexpr uint32 LockCountShift = 1;
    static constexpr uint32 LockCountMask = 0xffff'fffe;
 
    std::atomic<uint32> State = 0;
    std::atomic<uint32> ThreadId = 0;
};
 
} // UE
 
#undef UE_API