[PING][PATCH v2] [gdb] Prune inferior after switching inferior

Tom de Vries
2024-08-13T11:17:23Z

On 7/31/24 09:46, Tom de Vries 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.
>

Ping.

Thanks,
- Tom

> Tested on x86_64-linux.
>
> PR gdb/31440
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31440
> ---
> gdb/inferior.c | 4 +++
> .../gdb.python/py-progspace-events.exp | 31 +++----------------
> 2 files changed, 9 insertions(+), 26 deletions(-)
>
> diff --git a/gdb/inferior.c b/gdb/inferior.c
> index 6a197679902..bc9e5ee58d4 100644
> --- a/gdb/inferior.c
> +++ b/gdb/inferior.c
> @@ -790,6 +790,10 @@ inferior_command (const char *args, int from_tty)
> notify_user_selected_context_changed
> (USER_SELECTED_INFERIOR);
> }
> +
> + /* Switching current inferior may have made one of the inferiors
> + prunable, so prune it. */
> + prune_inferiors ();
> }
> }
>
> diff --git a/gdb/testsuite/gdb.python/py-progspace-events.exp b/gdb/testsuite/gdb.python/py-progspace-events.exp
> index 95e4ca8da0b..9dfc7573d40 100644
> --- a/gdb/testsuite/gdb.python/py-progspace-events.exp
> +++ b/gdb/testsuite/gdb.python/py-progspace-events.exp
> @@ -79,37 +79,16 @@ gdb_test "continue" \
> "\\\[Inferior $decimal \[^\r\n\]+ exited normally\\\]"] \
> "continue until inferior 2 exits"
>
> -gdb_test "inferior 1" "\\\[Switching to inferior 1 .*"
> -
> -# Step the inferior. During this process GDB will prune the now
> +# Switch to inferior 1. During this process GDB will prune the now
> # defunct inferior, which deletes its program space, which should
> # trigger the FreeProgspaceEvent.
> #
> -# However, there is a slight problem. When the target is remote, and
> -# GDB is accessing files using remote fileio, then GDB will attempt to
> -# prune the inferior at a point in time when the remote target is
> -# waiting for a stop reply. Pruning an inferior causes GDB to close
> -# files associated with that inferior.
> -#
> -# In non-async mode we can't send fileio packets while waiting for a
> -# stop reply, so the attempts to close files fails, and this shows up
> -# as an error.
> -#
> -# As this error has nothing to do with the feature being tested here,
> -# we just accept the error message, the important part is the
> -# 'FreeProgspaceEvent' string, so long as that appears (just once)
> -# then the test is a success.
> -set warning_msg \
> - [multi_line \
> - "warning: cannot close \"\[^\r\n\]+\": Cannot execute this command while the target is running\\." \
> - "Use the \"interrupt\" command to stop the target" \
> - "and then try again\\."]
>
> -gdb_test "step" \
> +gdb_test "inferior 1" \
> [multi_line \
> - "^FreeProgspaceEvent.*: <gdb.Progspace object at $hex>(?:\r\n$warning_msg)*" \
> - "do_parent_stuff \\(\\) at \[^\r\n\]+" \
> - "$decimal\\s+\[^\r\n\]+"]
> + "\\\[Switching to inferior 1 .*" \
> + ".*" \
> + "FreeProgspaceEvent.*: <gdb.Progspace object at $hex>"]
>
> # Let this inferior run to completion.
> gdb_continue_to_end
>
> base-commit: 762f95fdc65f9fb138d77bed44d77b8fd947dc44