Re: Linux threads support in GDB

[gdb at dontknow dot org]

On 02-Oct-00 Mark Kettenis wrote:
>    Date: Wed, 13 Sep 2000 18:25:21 -0600 (MDT)
>    From: gdb@dontknow.org
> 
> Appologies for the this late reply.  Meanwhile, the particular failing
> assertions you were seeing should be gone.
> 
>    Ok, here is a test case that will reproduce the problem (to some
>    extent anyways). I guess for some of my testing trying to reproduce
>    the problem with something similiar I was using GDB 5.0, not the
>    cvs version. However that version also has problems with the
>    following code.) Normally when I run the real application I have
>    SIGSTOP and SIGCONT set to nostop, which may be why it isn't seen
>    until a breakpoint is used, whereas here it happens after the
>    implicit SIGCONT breakpoint.
> 
> Hmm.  GDB heavily relies on SIGSTOP itself.  There is no other way to
> stop threads in Linux :-(.  Due to the nature of signals (particularly
> the fact that multiple signals might be merged into one), this rather
> hoplessly interferes with the SIGSTOPs you're using in your program.
> I really don't intend to fix this.  Sorry.

And my application requires the occassional use of SIGSTOP for stopping threads
(as you said, there is no other way to do it, at least not that I can find.)
However I am not exactly sure what the cause of the problem is. Especially
considering that a signal is sent to a single thread and not all threads (with
the possible exceptions of the main thread or signals from the shell). This
behavior is where Linux is different than standard PTHREADS (otherwise the use
of SIGSTOP would be a bad thing for my application.)

Another problem that I am seeing with the threading is that exiting threads
are ending up defunct rather than going away while using GDB (correct behavior
is seen w/o GDB). Is SIGCHLD is being handled correctly? IIRC that is the cause
of that.

> Mark
> 
> PS Please keep CC'ing the GDB mailing list.  These discussions could
> be useful for other people too.

Ok, I'll try to remember. I'm subscribed to the gdb-bug list but not the gdb
list.


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