[Qt-interest] SIGSEGV with single-line gdb backtrace

[Thiago Macieira]

Em Segunda-feira 28. Setembro 2009, às 03.38.33, Josiah Bryan escreveu:
> QThread: Destroyed while thread is still running

Put a breakpoint in this warning in qthread.cpp. (line 407 in Qt 4.5.2)

Your program will stop when it detects you destroyed a QThread that is still 
running. Fix these warnings first, because they indicate that there's a 
threading issue.

In another email, you said:
> Alright, I narrowed it down using the good old-fashioned
> "comment-out-lines-until-it-stops-crashing" method - and narrowed it
> down to an obscure place in the destructor of my video decoder QThread:
> At one point, I free all the libav stuff allocated, and one of the lines
> does this:
>
> av_free(m_av_frame);

You're probably freeing a pointer that is in-flight. This is a threading issue. 
I really recommend you use helgrind (which means upgrading valgrind).

Note that you said you're freeing in the destructor. And note that QThread 
warned you that the thread is *still* running. Therefore, it's probably still 
changing its data.

Conclusion: do not leave Qt warnings unfixed. Fix them all.
-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
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