Using QtConcurrent::run() with QMutex results in unexpected deadlock or warning.

I have created a simple application that demonstrates this error/behavior. The application is called qtThreads.exe and the source is listed at the bottom of this post.

In the following examples the application is being run from a Windows console.

See similar problem with QReadWriteLock: QTBUG-7886

Example #1 - Works as expected
qtThreads.exe && echo Test Complete

• Output:

  Non-Threaded
  Test Complete
  

Example #2 - Generates warning
qtThreads.exe wait && echo Test Complete

• Output:

  Threaded
  QWaitCondition: Destroyed while threads are still waiting
  Test Complete
  

Example #3 - Generates deadlock
qtThreads.exe nowait && echo Test Complete

• Output:

  Threaded
  

Source Code:

#include <QtCore/QtConcurrentRun>
#include <QtCore/QMutex>

#include <iostream>

void foo()
{
    QMutex lock;
    lock.lock();
    lock.unlock();
}

int main(int argc, char* argv[])
{
    if (argc > 1)
    {
        std::cerr << "Threaded\n";
        QFuture<void> future = QtConcurrent::run(&foo);

        if (strcmp(argv[1], "wait") == 0)
        {
            future.waitForFinished();
        }

    }
    else
    {
        std::cerr << "Non-Threaded\n";
        foo();
    }

    return 0;
}