[Bug breakpoints/19598] GDB breakpoint locks up Ubuntu UI, requiring reboot

["palves at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19598

--- Comment #11 from Pedro Alves <palves at redhat dot com> ---
(In reply to Dave Nadler from comment #10)
> OK, I managed to run the application from a non-GUI window with GDB, and
> found:
> - when GDB breaks, the GUI is locked up, and
> - if I "continue" in GDB, the GUI resumes normal operation

OK, this really doesn't look like a GDB problem then.

> 
> Leaves the question:
> 
> 1) Most important: How can I prevent what-ever lockup is occurring on a GDB
> breakpoint? This is really impeding work on this particular project;  its
> enormously easier and more productive to work in Eclipse than with raw GDB...

When the breakpoint triggers, the whole process is halted (all its threads).
Sounds like there's a held thread that was doing something important for the
GUI.

You could e.g., try "thread apply all bt" to get a backtrace of all threads,
and maybe that'll give you a clue to which thread that might be, and then what
is its connection with the GUI.

Alternatively, debug in non-stop mode, so that only the thread that hits the
breakpoint is halted and the rest of the process's threads continue running.

You could try debugging in non-stop mode and interrupt/suspend threads one by
one (instead of setting a breakpoint).  Maybe you'll find which thread it is
that way.

>From the name of the function (InputEvents::eventDRNtestHook), I'd suspect the
very same thread that hits that breakpoint though...   After the breakpoint
triggers, instead of "continue", I'd try stepping through that code until the
GUI starts working, in order to determine what is the code doing to make the
GUI responsive again.

> 
> 2) Why did debugging with this exact breakpoint work a few months ago?
> There's been to my knowledge no change in the application structure (for
> example grab functions etc)...

Sorry, crystal ball broken... ;-)

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