[Interest] QTimer Freeze in 4.8

[Thiago Macieira]

On quarta-feira, 22 de junho de 2016 14:49:39 PDT Cjb_SW Freescale wrote:
> yes and no, I mean that every other process is executed proper by Linux,
> and also a second QThread running in the GUI application is running fine.
> Seems that only the graphic Thread is "freezed". It will resume by touching
> the Touchscreen (which is USB, managed via Tslib).
> 
> Unfortunately I cannot build backtraces, I have problems with GDB. I can
> launch the program under gdbserver, and I can set breakpoints, but if I
> press the Interrupt button, then I can see a disassembly window, and I
> can't see where it is the programcounter in my sources. So I tried to
> Interrupt the application while is in the freeze state, but I can't see
> something useful.

Please, always reply to the mailing list. If you reply to me personally, it 
may get lost in inbox and I may never reply. And no one else would have the 
opportunity to, either.

Anyway, since you said that other processes are running just fine and even 
other threads in the same process, my conclusion is that something is blocking 
the GUI thread in your application. We've seen this happen in Qt 5 with XCB, 
whenever the screensaver is on or when you swap to another virtual terminal: 
there's a function call we make that blocks on waiting for a reply from the X 
server, which won't come until the display is unlocked.

Clearly that's not your case, but you get the idea of what it might be.

Unfortunately, I can't help you without a backtrace (and one with debug 
symbols, at that). I have NEVER built a QWS build of Qt and I don't even have 
a Qt 4.8 source handy to look things up. Sorry.

My recommendations are:
 * fix GDB. It's unacceptable for it not to work.
 * consider upgrading to Qt 5.6 or 5.7 (which means dropping QWS for something 
    else)

Note that you can work around a non-working gdbserver by causing your process 
to dump core while in the frozen state (kill -ABRT, for example), then loading 
that core file on your host machine's target gdb.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center