Re: Daniel, thread vs. fork question.

[Daniel Jacobowitz <drow@mvista.com>]

On Thu, Mar 11, 2004 at 01:08:40AM +0000, Michael Snyder wrote:
> Hey Daniel,
> 
> Got a question concerning the code in 
> linux-nat.c::linux_handle_extended_wait.
> 
> You've got a PTRACE_EVENT_FORK event, and now you're going to call 
> waitpid.  You pull a pid out of a list of stopped pids, and wait for
> it using waitpid.  In your comment, you explain that you don't have to
> worry about the pid being a clone, because you didn't ask for pids in
> the event mask.
> 
> But how is this affected by threads, especially NPTL threads?
> I've got a fairly simple test-case (modified from pthreads.c,
> I'll attach it), in which a child thread calls fork -- but gdb
> apparently tries to wait on the main thread (or perhaps the most
> recent event thread).  Since that's not the thread that called
> fork, waitpid returns -1 with "no child".  Gdb reports:
> 	waiting for new child: No child processes.
> 
> FWIW, I've tried this on both a single-processor and an SMP machine.

No attachment?  Also, what glibc/nptl version are you using.

It's entirely possible that I didn't handle some threaded case.  But we
save the PID that we plan to wait on, which should be the child thread,
so I don't see how what you're describing can happn.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer