Parallel calculation leads to random corruption of the results

nulluse

I am learning Qt parallel namespace on the Mandelbrot set test app.
When I run regular single-threaded calculation over the data vector, the result is always the same.
But when the parallel calculation runs using QtConcurrent::map, the results become corrupt after about 300,000 elements of the vector and corruption is seemingly random (the last screen shows that no corruption occurred even though the 1st and 2nd were corrupt).

Attaching the Zipped Netbeans project and the screenshots of parallel computation.
Project
Snapshot1
Snapshot2
Snapshot3

Can anyone please point me in the right direction of what I am doing wrong?

Thank you!

SGaist

Hi,

You don't wait for map to finish before updating the picture.

nulluse

Excellent, I totally mis-read the tutorials and was convinced that assigning to the future was supposed to do that.
Now this works perfect:

    QFutureWatcher<void> fw;
    fw.setFuture(QtConcurrent::map(vec, mandelbrot));    
    fw.waitForFinished();

SGaist

Since you want to do multithreading, why not use the finished signal ? Beware, you'll have to refactor the code a bit.