[PING^2][PATCH] [gdb] Prune inferior after switching inferior

[Tom de Vries <tdevries@suse.de>]

On 3/19/24 10:34, Tom de Vries wrote:
> On 3/4/24 13:21, 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 1, 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 1
>> 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
>> ...
>>
>> Tested on x86_64-linux.
>>
> 
> Ping.

Ping^2.

Thanks,
  Tom

>> 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 5ff5eb98955..4e179f7fb80 100644
>> --- a/gdb/inferior.c
>> +++ b/gdb/inferior.c
>> @@ -791,6 +791,10 @@ 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: 1485a3fb63619cced99dd7a4a043cf01a0f423d9
>