Best way to send data from a GUI thread to a processing thread?

[dmginc]

Reasonable - sure.
But its hard to tell exactly without getting deeper in to the logic of your application.

The only non related comment I have is that you are locking the mutex basically the hole run() duration, which is not good - it is legal, but it cause your application or parts of the logic to wait longer they they should/could.
You should only mutex where data is accessed, and try to be as atomic as possible.

Thanks - I must point out that the slots (connected to signals triggered by the main window GUI) in the ProcessingThread are quite short and only copy a small amount of data. As I said before, my goal in using the mutexes is merely to make sure the update of the flags/settings is predictable and does not occur in the middle of processing. So it looks like the maximum penalty I would pay is a one iteration delay of run() in updating these flags/settings I guess...
Would you agree?

On a related note: When using mutexes to protect different data in the same thread, should I declare seperate mutexes?

eg:

void ProcessingThread::run()
{
    while(1)
    {
    frame=grabFrame();
    mutex.lock();
    if(flag1)
         doProcessingOnFrame1(frame,setting1,setting2);
    if(flag2)
         doProcessingOnFrame2(frame,setting3,setting4);
    if(flag3)
         doProcessingOnFrame3(frame,setting5,setting6);
    mutex.unlock();
    emit newFrame(frame);
    mutex2.lock();
   updateFPSvalue(); // saves current FPS value in a private member (this member is accessed by the GUI thread using a "get" function containing a QMutexLocker)
   mutex2.unlock();
    }
}

void ProcessingThread::run()
{
    while(1)
    {
    frame=grabFrame();
    mutex.lock();
    if(flag1)
         doProcessingOnFrame1(frame,setting1,setting2);
    if(flag2)
         doProcessingOnFrame2(frame,setting3,setting4);
    if(flag3)
         doProcessingOnFrame3(frame,setting5,setting6);
    mutex.unlock();
    emit newFrame(frame);
    mutex2.lock();
   updateFPSvalue(); // saves current FPS value in a private member (this member is accessed by the GUI thread using a "get" function containing a QMutexLocker)
   mutex2.unlock();
    }
}

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Thanks again.