[Qt-interest] End thread when work is done

[Cole, Derek]

This may be the case, indeed, but I must have some way to kill the active threads. It doesnt seem like QtConcurrent will let me to create more runnables than I have maxThreadCount() - so how would I know how many threads I can make? My intent is to max out the number of threads running processing a file, when that file is finished, load another and so-on.

Here is the complete code

    QStringList files = dir.entryList();
    for(int i = 0; i < files.size(); i++)
    {

        filename = dir.absolutePath() +"/" + files.at(i);

        QFutureWatcher<void> *copywatcher;
        copywatcher = new QFutureWatcher<void>();
        QFuture<void> copyfuture = QtConcurrent::run(this, &EraserBatch::copyFile,filename);
        copywatcher->setFuture(copyfuture);

        QFutureWatcher<void> *loadwatcher;
        loadwatcher = new QFutureWatcher<void>();
        QFuture<void> loadfuture = QtConcurrent::run(this, &EraserBatch::loadTiles,filename);
        loadwatcher->setFuture(loadfuture);

        std::vector<QFutureWatcher<bool> * > procWatchers;
        std::vector<QFuture<bool> > procFutures;
        int maxThreads = QThreadPool::globalInstance()->maxThreadCount();
        int activeThreads =  QThreadPool::globalInstance()->activeThreadCount();

        for(int j = 0; j < maxThreads - activeThreads; j++ )
        {
            QFutureWatcher<bool> *procwatcher;
            procwatcher = new QFutureWatcher<bool>();
            procWatchers.push_back(procwatcher);
            QFuture<bool> procfuture = QtConcurrent::run(this, &EraserBatch::processTile);
            procFutures.push_back(procfuture);
            procwatcher->setFuture(procfuture);

        }

    //   // only do one file at once, so wait until copy/write is done
        qDebug()<<"Waiting for finish";
        copywatcher->waitForFinished();
    }

so as you can see, I have one thread loading the file, one thread creating a copy that will be over-written with results, and then I want to spawn MAX-2 threads to do the actual processing.

This seems to not be working the way I have it written here. copyWatcher does the write-out of the results, so presumably when it is done, I could do all the work over again with the same number of threads on the next file in the directory

Derek
________________________________________
From: qt-interest-bounces+dcole=integrity-apps.com at qt.nokia.com [qt-interest-bounces+dcole=integrity-apps.com at qt.nokia.com] on behalf of Andreas Pakulat [apaku at gmx.de]
Sent: Wednesday, August 17, 2011 3:00 PM
To: qt-interest at qt.nokia.com
Subject: Re: [Qt-interest] End thread when work is done

On 17.08.11 18:31:10, Cole, Derek wrote:
> Hello, I have the following:
>
>         int maxThreads = QThreadPool::globalInstance()->maxThreadCount();
>         int activeThreads =  QThreadPool::globalInstance()->activeThreadCount();
>
>         for(int j = 0; j < maxThreads - activeThreads; j++ )
>         {
>             QFutureWatcher<bool> *procwatcher;
>             procwatcher = new QFutureWatcher<bool>();
>             procWatchers.push_back(procwatcher);
>
>
>             QFuture<bool> procfuture = QtConcurrent::run(this, &EraserBatch::processTile);
>             procFutures.push_back(procfuture);
>             procwatcher->setFuture(procfuture);
>             qDebug()<<"Active threadcount after proc "<<QThreadPool::globalInstance()->activeThreadCount();
>
>         }
>
> when "processTile" is finished running for each of these, the method
> returns fine, but when I check the activeThreadCount, it shows all of
> them still running. What can I put to make sure that each thread ends
> when the method to run has ended?

I think you may mis-interpret what activeThreadCount tells you. I can't
see any indication that QThreadPool kills threads when the runnable is
done. A thread started by QThreadPool probably simply waits until more
work is to be done, otherwise the whole pool-idea would not make much
sense.

Andreas

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