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Daniel, thread vs. fork question.
- From: Michael Snyder <msnyder at redhat dot com>
- To: Daniel Jacobowitz <drow at mvista dot com>, gdb-patches at sources dot redhat dot com
- Date: Thu, 11 Mar 2004 01:08:40 +0000
- Subject: Daniel, thread vs. fork question.
- Organization: Red Hat, Inc.
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.
Michael