Re: [PATCH] run-command: don't spam trace2_child_exit()

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 28, 2022, 21:46 UTC
Message-ID: <xmqqr15gev94.fsf@gitster.g>
In-Reply-To: <4616d09ffa632bd2c9e308a713c4bdf2a1328c3c.1651179450.git.steadmon@google.com>

Josh Steadmon <steadmon@google.com> writes:

> In rare cases, wait_or_whine() cannot determine a child process's exit
> status (and will return -1 in this case). This can cause Git to issue
> trace2 child_exit events despite the fact that the child is still
> running.

Rather, we do not even know if the child is still running when it happens, right? It is curious what "rare cases" makes the symptom appear. Do we know?

The patch looks OK from the "we do not know the child exited in this case, so we shouldn't be reporting the child exit" point of view, of course. Having one event that started a child in the log and then having millions of events that reports the exit of the (same) child is way too broken. With this change, we remove these phoney exit events from the log.

Do we know, for such a child process that caused these millions phoney exit events, we got a real exit event at the end? Otherwise, we'd still have a similar problem in the opposite direction, i.e. a child has a start event recorded, many exit event discarded but the log lacks the true exit event for the child, implying that the child is still running because we failed to log its exit?

Show 8 quoted lines

>  int finish_command_in_signal(struct child_process *cmd)
>  {
>  	int ret = wait_or_whine(cmd->pid, cmd->args.v[0], 1);
> -	trace2_child_exit(cmd, ret);
> +	if (ret != -1)
> +		trace2_child_exit(cmd, ret);
>  	return ret;
>  }

Will queue; thanks.