App hangs in QPixmap::fromImage

Christian Ehrlicher

Again: it hangs on a mutex lock - nothing to do with the data. Take a look if this mutex is locked in another thread...

mpouchol

@Christian-Ehrlicher the mutex is owned by Qt code inside QPixmap::fromImage
I don't use this function from other threads so I don't see what I did that caused it to stay locked.

Christian Ehrlicher

@mpouchol said in App hangs in QPixmap::fromImage:

I don't use this function from other threads so I don't see what I did that caused it to stay locked.

I'm giving up... looks like it's too hard to look into the other threads while it is hanging to see if another thread is also using this mutex. So try to figure it out by your own.

mpouchol

@Christian-Ehrlicher said in App hangs in QPixmap::fromImage:

I'm giving up... looks like it's too hard to look into the other threads

I did that and that's not the case. Thanks for your help anyway.

Christian Ehrlicher

Ok, taking a deeper look into convert_generic() the qimage is converted with more than one thread. One of these subthreads hangs maybe due to a broken QImage. Look into your other threads to see which one is somewhere hanging inside convertSegment()

mpouchol

I also had a look at the code inside convert_generic(). When the main thread is frozen I don't see other threads hanging in convertSegment which make me think that maybe one of the convertSegment threads has died silently and is not releasing the semaphore in convert_generic because I don't see visual studio raising exceptions in other threads.

Christian Ehrlicher

If you compile Qt by your own build a big try/catch block around convert_segment and simply catch all exceptions to see if there is one.
You can also create a helper thread which writes out the current qimage after a certain period of time when it was not canceled in between so you can inspect the qimage.

Christian Ehrlicher

Ah, see https://bugreports.qt.io/browse/QTBUG-90629 and https://bugreports.qt.io/browse/QTBUG-92188 even I don't see how this should affect windows.

mpouchol

@Christian-Ehrlicher said in App hangs in QPixmap::fromImage:

https://bugreports.qt.io/browse/QTBUG-90629

Indeed when looking at the stack trace it looks very similar to my case, almost the same function calls except for the low level semaphore things on linux.

I think I may have to rebuild Qt and try your suggestion to wrap convert_segment around a try/catch block to have more detail.

Gerald Lodron

@mpouchol
I updated my (working) software from 5.12.11 to 5.15.8 and have exactly the same problem, now the QPixmap::fromImage hangs. I did not debugged into qt but its defenitely in main thread and its my only and first call of it. It happens every time in my case, the image is a Format_Grayscale8 too

is there a solution for it?

Gerald Lodron

it really seems to have something to do with Format_Grayscale8, Format_RGB888 and QImage::Format_Mono works...

X-Hawk

There must be some bug in QThreadPool cause QPixmap hangs.
Set setExpiryTimeout to -1 may help, just a workaround, not bug fix.

QThreadPool *threadPool = QThreadPool::globalInstance();
if (threadPool) {
    threadPool->setExpiryTimeout(-1);
}