PThreadEvent.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
// HEADER_UNIT_UNSUPPORTED - Unsupported platform
 
#include "Misc/AssertionMacros.h"
#include "HAL/Event.h"
 
/**
 * This is the PThreads version of FEvent.
 */
class FPThreadEvent
    : public FEvent
{
    // This is a little complicated, in an attempt to match Win32 Event semantics...
    typedef enum
    {
        TRIGGERED_NONE,
        TRIGGERED_ONE,
        TRIGGERED_ALL,
    } TriggerType;
 
    bool bInitialized;
    bool bIsManualReset;
    volatile TriggerType Triggered;
    volatile int32 WaitingThreads;
    pthread_mutex_t Mutex;
    pthread_cond_t Condition;
 
    inline void LockEventMutex()
    {
        const int rc = pthread_mutex_lock(&Mutex);
        check(rc == 0);
    }
 
    inline void UnlockEventMutex()
    {
        const int rc = pthread_mutex_unlock(&Mutex);
        check(rc == 0);
    }
 
    static inline void SubtractTimevals( const struct timeval *FromThis, struct timeval *SubThis, struct timeval *Difference )
    {
        if (FromThis->tv_usec < SubThis->tv_usec)
        {
            int nsec = (SubThis->tv_usec - FromThis->tv_usec) / 1000000 + 1;
            SubThis->tv_usec -= 1000000 * nsec;
            SubThis->tv_sec += nsec;
        }
 
        if (FromThis->tv_usec - SubThis->tv_usec > 1000000)
        {
            int nsec = (FromThis->tv_usec - SubThis->tv_usec) / 1000000;
            SubThis->tv_usec += 1000000 * nsec;
            SubThis->tv_sec -= nsec;
        }
 
        Difference->tv_sec = FromThis->tv_sec - SubThis->tv_sec;
        Difference->tv_usec = FromThis->tv_usec - SubThis->tv_usec;
    }
 
public:
 
    FPThreadEvent()
    {
        bInitialized = false;
        bIsManualReset = false;
        Triggered = TRIGGERED_NONE;
        WaitingThreads = 0;
    }
 
    virtual ~FPThreadEvent()
    {
        // Safely destructing an Event is VERY delicate, so it can handle badly-designed
        //  calling code that might still be waiting on the event.
        if (bInitialized)
        {
            // try to flush out any waiting threads...
            LockEventMutex();
            bIsManualReset = true;
            UnlockEventMutex();
            Trigger();  // any waiting threads should start to wake up now.
 
            LockEventMutex();
            bInitialized = false;  // further incoming calls to this object will now crash in check().
            while (WaitingThreads)  // spin while waiting threads wake up.
            {
                UnlockEventMutex();  // cycle through waiting threads...
                LockEventMutex();
            }
            // No threads are currently waiting on Condition and we hold the Mutex. Kill it.
            pthread_cond_destroy(&Condition);
            // Unlock and kill the mutex, since nothing else can grab it now.
            UnlockEventMutex();
            pthread_mutex_destroy(&Mutex);
        }
    }
 
    // FEvent interface
 
    virtual bool Create( bool _bIsManualReset = false ) override
    {
        check(!bInitialized);
        bool RetVal = false;
        Triggered = TRIGGERED_NONE;
        bIsManualReset = _bIsManualReset;
 
        if (pthread_mutex_init(&Mutex, nullptr) == 0)
        {
            if (pthread_cond_init(&Condition, nullptr) == 0)
            {
                bInitialized = true;
                RetVal = true;
            }
            else
            {
                pthread_mutex_destroy(&Mutex);
            }
        }
        return RetVal;
    }
 
    virtual bool IsManualReset() override
    {
        return bIsManualReset;
    }
 
    virtual void Trigger() override
    {
        TriggerForStats();
 
        check(bInitialized);
 
        LockEventMutex();
 
        if (bIsManualReset)
        {
            // Release all waiting threads at once.
            Triggered = TRIGGERED_ALL;
            int rc = pthread_cond_broadcast(&Condition);
            check(rc == 0);
        }
        else
        {
            // Release one or more waiting threads (first one to get the mutex
            //  will reset Triggered, rest will go back to waiting again).
            Triggered = TRIGGERED_ONE;
            int rc = pthread_cond_signal(&Condition);  // may release multiple threads anyhow!
            check(rc == 0);
        }
 
        UnlockEventMutex();
    }
 
    virtual void Reset() override
    {
        ResetForStats();
 
        check(bInitialized);
        LockEventMutex();
        Triggered = TRIGGERED_NONE;
        UnlockEventMutex();
    }
 
    virtual bool Wait( uint32 WaitTime = (uint32)-1, const bool bIgnoreThreadIdleStats = false ) override;
};