PThreadSemaphore.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Misc/Timespan.h"
#include "Misc/AssertionMacros.h"
#include <pthread.h>
#include <errno.h>
#include <semaphore.h>
 
class FPThreadSemaphore
{
public:
    UE_NONCOPYABLE(FPThreadSemaphore);
 
    FPThreadSemaphore(int32 InitialCount, int32 MaxCount)
    {
        int Res = sem_init(&Semaphore, /*pshared = */ 0, InitialCount);
        checkfSlow(Res == 0, TEXT("Failed to create semaphore (%d:%d): %d"), InitialCount, MaxCount, errno);
    }
 
    ~FPThreadSemaphore()
    {
        int Res = sem_destroy(&Semaphore);
        checkfSlow(Res == 0, TEXT("Error destroying semaphore: %d"), errno);
    }
 
    void Acquire()
    {
        int Res = sem_wait(&Semaphore);
        checkfSlow(Res == 0, TEXT("Acquiring semaphore failed: %d"), errno);
    }
 
    bool TryAcquire(FTimespan Timeout = FTimespan::Zero())
    {
        timespec ts;
        int Res = clock_gettime(CLOCK_REALTIME, &ts);
        checkfSlow(Res == 0, TEXT("clock_gettime failed: %d"), errno);
 
        ts.tv_sec += (uint64)Timeout.GetTotalSeconds();
        ts.tv_nsec += Timeout.GetFractionNano();
        Res = sem_timedwait(&Semaphore, &ts);
        checkfSlow(Res == 0 || Res == ETIMEDOUT, TEXT("sem_timedwait failed: %d"), errno);
        return Res == 0;
    }
 
    void Release(int32 Count = 1)
    {
        checkfSlow(Count > 0, TEXT("Releasing semaphore with Count = %d, that should be greater than 0"), Count);
        for (int i = 0; i != Count; ++i)
        {
            int Res = sem_post(&Semaphore);
            checkfSlow(Res == 0, TEXT("Releasing semaphore failed: %d"), errno);
        }
    }
 
private:
    sem_t Semaphore;
};
 
typedef FPThreadSemaphore FSemaphore;