[solved] How to make a code to wait while a file is written on hard drive?

[mlong]

Of course, if you're using QPixmap outside the main thread, then you're bound to have troubles.

[peterm]

There is no much to show, the code is very simple. And it works fine when I need to save a single image. It leads to the crush only when image savings happen very frequently.

@
int AppWind::updateImage()
{
...

if (iterCurrent%iterPerOut==0) {
frame2d.saveImage();
...
}
}

bool Tp2dFrame::saveImage()
{
QPixmap* pm = getPixmap();
return pm->save(imageFileName);
}
@

[EDIT: code formatting, please wrap in @-tags, Volker]

[mlong]

(Please wrap your code in @ tags.)

Have you tried running the program under the debugger to find out exactly where the crash is occurring?

Again, just double checking... this is not running in a separate thread, correct?

[peterm]

Actually, there is a question about threads, because AppWind::updateImage() is a time consuming routine and is run by a separate thread. Any advice? Thanks.

[mlong]

Is that separate thread using QPixmaps? If it is, that's going to cause you problems.

QImages should be safe, if I remember correctly, though.

[peterm]

Debugging does not help in this case. When doing debugging step-by-step, then everything goes just fine, no crashes, I think because it's not fast enough. If I allow the code to run then it crashes with the error message "Fatal IO error 11 (Resource temporarily unavailable) on X server", and no other information can be obtained.

[peterm]

A separate thread calls AppWind::updateImage(), which in turn calls Tp2dFrame::saveImage(), which gets pixmap and saves it to a file: QPixmap* pm = getPixmap(); pm->save(imageFileName);

[reactive]

Then you need a traffic cop so cars don't crash into one another at the intersection. See my links above.

[peterm]

I tried to use the safe-thread methods as well, by using QMutexLocker locker(&mutex), but nothing helps. Maybe the problem is that the image changes too fast while the save() operation is still in process. Could it cause a crash?

[mlong]

Again, if you're using QPixmaps in another thread (or in code that's called from another thread) you're going to have issues, whether you're using mutexes or not.

[peterm]

mlong,
I've fixed the problem as you advised: the main thread should operate on QPixmaps. Thank you so much.

[mlong]

Good deal. Glad to help! Please be sure and edit the title of the thread to add [Solved]. Thanks!