autoLoader/threadData.cpp

//
//  Copyright 2012 Autodesk, Inc.  All rights reserved.
//
//  Use of this software is subject to the terms of the Autodesk license 
//  agreement provided at the time of installation or download, or which 
//  otherwise accompanies this software in either electronic or hard copy form.   
//

//-----------------------------------------------------------------------------

#include "threadData.h"
#include "moduleLogic.h"
#include <maya/MCommonSystemUtils.h>
#include <maya/MSpinLock.h>

#include <thread>
#include <chrono>

/*static*/ volatile bool threadData::bThreadToExecute =true ;
/*static*/ volatile bool threadData::bWaitingForCommand =false ;
static threadData tdata ;

struct _threadData *threadData::getThreadData () {
    return (&tdata) ;
}

//-----------------------------------------------------------------------------
// Compute function. This function is called from multiple asynchronous threads
MThreadRetVal threadData::AsyncModuleThread (void *data) {
    threadData *myData =(threadData *)data ;
    while ( threadData::bThreadToExecute ) {
        int ithreadDataDelay =threadDataDelayDefault ;
        char *val =getenv (threadDataDelayName) ;
        if ( val != NULL && *val != _T('\0') )
            ithreadDataDelay =atoi (val) ;

        MModuleLogic::ModuleDetectionLogicCmdExecute (myData) ;
        std::this_thread::sleep_for(std::chrono::seconds(ithreadDataDelay));
    }
    return (0) ;
}

//-----------------------------------------------------------------------------
// Variable to track threads. As each thread finishes it's work it
// increments this variable. The main thread will wait until this
// variable is equal to the thread count, meaning all threads have
// completed their work variable will equal the thread count
static volatile int g_async_count =0 ;
static MSpinLock asyncSpinLock ;

// Thread completion callback.
// Increment thread completion variable. Uses a lock to prevent race
// conditions where two threads attempt to update the variable simultaneously
void threadData::AsyncModuleThreadEnded (void *data) {
    asyncSpinLock.lock () ;
    g_async_count++ ;
    asyncSpinLock.unlock () ;
}

MStatus threadData::startThread () {
    // Define Thread Laps as an environment variable
    if ( MCommonSystemUtils::getEnv (threadDataDelayName) == "" )
    {
        MCommonSystemUtils::putEnv (threadDataDelayName, szthreadDataDelayDefault) ;
    }

    // Start threads. Each thread makes a call to AsyncModuleThread
    // The stopThread function called in uninitializePlugin() waits until 
    // all threads have completed (but we got only one here).
    threadData::bThreadToExecute =true ;
    threadData::bWaitingForCommand =false ;
    MStatus ms =MThreadAsync::init () ;
    if ( ms != MS::kSuccess )
        return (ms) ;
    ms =MThreadAsync::createTask (
        threadData::AsyncModuleThread,
        (void *)threadData::getThreadData (),
        threadData::AsyncModuleThreadEnded,
        NULL
    ) ;
    return (ms) ;
}

//-----------------------------------------------------------------------------
// Test if variable matches the expected value. Locks required to
// ensure thread safe access to variables.
/*static*/ MSpinLock threadData::exchangeSpinLock ;

bool threadData::Maya_InterlockedCompare (volatile int *variable, int compareValue) {
    exchangeSpinLock.lock () ;
    bool rtn =(*variable == compareValue) ;
    exchangeSpinLock.unlock () ;
    return (rtn) ;
}

// Barrier function. Main thread enters here and polls the count
// variable until all worker threads have indicated they have
// completed by incrementing this count.
void threadData::WaitForAsyncThreads (int val) {
    while ( !threadData::Maya_InterlockedCompare (&g_async_count, val)) {
        std::this_thread::yield();
    }
}

void threadData::stopThread () {
    // Ask the thread to terminate
    threadData::bThreadToExecute =false ;

    // Waits until all threads have completed before continuing
    threadData::WaitForAsyncThreads (1) ;
    MThreadAsync::release () ; // release async thread
}