Re: [PATCH v2] [gdb] Prune inferior after switching inferior

[Kevin Buettner <kevinb@redhat.com>]

On Wed, 31 Jul 2024 09:46:05 +0200
Tom de Vries <tdevries@suse.de> wrote:

> Usually with test-case gdb.python/py-progspace-events.exp I get:
> ...
> (gdb) inferior 1^M
> [Switching to inferior 1 [process 4116] (py-progspace-events)]^M
> [Switching to thread 1.1 (Thread 0xf77d0ce0 (LWP 4116))]^M
> 28      { /* Nothing.  */ }^M
> (gdb) PASS: gdb.python/py-progspace-events.exp: inferior 1
> step^M
> FreeProgspaceEvent: <gdb.Progspace object at 0xabf4f850>^M
> do_parent_stuff () at py-progspace-events.c:41^M
> 41        ++global_var;^M
> (gdb) PASS: gdb.python/py-progspace-events.exp: step
> ...
> 
> But occasionally I run into the following FAIL:
> ...
> (gdb) inferior 1^M
> [Switching to inferior 1 [process 5199] (py-progspace-events)]^M
> [Switching to thread 1.1 (Thread 0xf77d0ce0 (LWP 5199))]^M
> 28      { /* Nothing.  */ }^M
> (gdb) FreeProgspaceEvent: <gdb.Progspace object at 0xabaf03a0>^M
> FAIL: gdb.python/py-progspace-events.exp: inferior 1 (timeout)
> ...
> 
> This is caused by a race between the handling of an event, and the
> "inferior 1" command.
> 
> In the passing case, the event is handled first.  During which prune_inferiors
> is called, but it can't remove inferior 2, because it's still the current one.
> 
> In the failing case, the "inferior 1" command is handled first.  Then during
> handling of the event, prune_inferiors is called, and it can remove inferior 2
> because it's no longer the current one.
> 
> This looks like a test-case issue to me, but ISTM that we can do better: by
> calling prune_inferiors asap, at the end of the "inferior 1" command, we
> stabilize the moment when the inferior is removed:
> ...
> (gdb) inferior 1^M
> [Switching to inferior 1 [process 5199] (py-progspace-events)]^M
> [Switching to thread 1.1 (Thread 0xf77d0ce0 (LWP 5199))]^M
> 28      { /* Nothing.  */ }^M
> FreeProgspaceEvent: <gdb.Progspace object at 0xabaf03a0>^M
> (gdb) PASS: gdb.python/py-progspace-events.exp: inferior 1
> ...
> 
> This also allows us to simplify the test-case by removing the step command,
> which is no longer required to trigger the pruning of the inferior.
> 
> Tested on x86_64-linux.
> 
> PR gdb/31440
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31440

Approved-by: Kevin Buettner <kevinb@redhat.com>