gdb and multi-threaded applications.

[Kevin Buettner]

On Mar 10,  1:03pm, jjs wrote:

> Sorry I have not been back to you sooner, I have been distracted by other
> things. I tried getting a test application to exhibit the same behaviour
> with no luck. However, I did notice that before the call to pthread_create
> to start up the new thread we have the line:
>
>     pthread_sigmask(SIG_BLOCK, &fullSigMask, &sigMask);
>
> All the bits in fullSigMask are set, so this call blocks all signals to the
> calling thread. Commenting this line out makes everything work under gdb,
> the new thread gets created and doing 'info threads' after this gives me a
> list of all the threads running in the process. This implies that gdb
> requires a signal to be unblocked at the point the thread is created. If
> this is fact the case, which signal must we not block in order for correct
> operation under gdb?

SIGCHLD.

(I think.)

Background for Michael: Jerry reported a problem in which gdb (on
linux/ppc) hangs on a pthread_create().   Jerry has verified that
the thread tests in the test suite work properly on his platform,
so we know that gdb does work (some of the time) when creating
new threads.  Jerry's application is proprietary and I've asked him
to try to distill the problem into a small example that we can test.

Note to Jerry: I'd still like a small example, preferably one that
we could eventually put into the testsuite.

Kevin

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