[Qt-creator] App crashes if signals come to fast in debug mode?

[André Pönitz]

On Tue, Dec 11, 2018 at 07:24:00PM +0000, Murphy, Sean wrote:
> First, not sure if this is really a Qt Creator question or a general
> Qt question, so feel free to suggest I move this over to qt-interest
> if you think it fits better there.
> 
> When debugging an application within Qt Creator, is there any reason
> that an application would crash by sending signals to a
> QProgressDialog too quickly?

Depends on context, but, sure, it's imaginable.

An "Evaluated Expression"  malloc(100....) + possibly actually
writing to the memory would happily leak until the process
runs out of memory.

Similar situations occur for certain types that require executing
code to display, etc, etc.

> The setup: Our application programs a flash based device over the
> serial port. I have the programming object running in a separate
> thread from the GUI, and then there's a QProgressDialog in the main UI
> thread that shows the status of the programming. These two objects
> communicate via a signal: void sigPageProgrammed(int currentPage, int
> totalPageCount). We program the device in 256 byte pages, with 1024
> pages total. As part of that programming process, we check to see if
> the page is "empty" (all bytes equal 0xff within a given 256 byte
> block). If it's empty, we skip it to save time. I realized while
> testing that I was only emitting that sigPageProgrammed() signal when
> we actual wrote a page, and didn't emit anything when we get to skip
> an empty page. One of our devices only uses the first 180 pages, so
> when programming that device, the progress dialog increments from 0 to
> 17% and then doesn't increment anymore since the rest of the pages are
> blank.
> 
> So I figured I'd add code to emit that signal even on the empty pages
> just so that the progress bar will always see 0 to 100%, regardless of
> how many pages need to get programmed. Once I made that change, and
> I'm 100% sure that's the only change I made, the application now
> segfaults when running in debug mode at the following line in a slot
> that is connected to the above signal: void
> MainWindow::slotProgrammingStatus(int current, int total) {
> if(mDlgProgrammingProgress->maximum() != total) {
> mDlgProgrammingProgress->setMaximum(total); }
> mDlgProgrammingProgress->setValue(current); // <- segfault happens
> here qDebug() << "Programming page" << current << "of" << total; }
> 
> If I rebuild the application in release mode, and run it either from
> within Qt Creator (using CTRL+R) or run it outside Qt Creator
> altogether it runs just fine without crashing, only crashing inside Qt
> Creator and only in debug mode. 

When debugging or running the application when compiled in debug mode?

> So the only real difference I see is
> that for the first 17% of programming, the signals are coming out
> fairly slowly, after that, the next clump of signals are going to come
> out much faster based on how quickly that programming thread can
> determine that each of the remaining pages are empty.
> 
> Any ideas?

Open an issue on bugreports.qt-project.org and attach a debugger log
(contents of right pane of Windows->Views->Debugger Log) there.

Andre'


> Sean

PS:
 
> tHIS MEssage has been scanned for malware by Forcepoint.

And what was the result?

SCNR.