Subject: Re: [PATCH] transport-helper: check when helpers fail

From: Johannes Sixt <[email-masked]>
Date: Mon, 22 Oct 2012 08:35:29 +0200

Am 10/21/2012 21:19, schrieb Felipe Contreras:
> diff --git a/run-command.c b/run-command.c
> index 1101ef7..2852e9d 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -559,6 +559,23 @@ int run_command(struct child_process *cmd)
>  	return finish_command(cmd);
>  }
>  
> +int check_command(struct child_process *cmd)
> +{
> +	int status;
> +	pid_t pid;
> +
> +	pid = waitpid(cmd->pid, &status, WNOHANG);
> +
> +	if (pid < 0)
> +		return -1;
> +	if (WIFSIGNALED(status))
> +		return WTERMSIG(status);
> +	if (WIFEXITED(status))
> +		return WEXITSTATUS(status);
> +
> +	return 0;
> +}
> +

In this form, the function is not suitable as a public run-command API: If
the child did exit, it does not allow finish_command() to do its thing.
The only thing the caller of this function can do is to die() if it
returns non-zero. It doesn't report treat error cases in the same way as
wait_or_whine().

I would expect the function to be usable in this way:

	start_command(&proc);

	loop {
		if (check_command(&proc))
			break;
	}

	finish_command(&proc);

but it would require a bit more work because it would have to cache the
exit status in struct child_process.

BTW, you should check for return value 0 from waitpid() explicitly.

Another thought: In your use-case, isn't it so that it would be an error
that the process exited for whatever reason? I.e., even if it exited with
code 0 ("success"), it would be an error because it violated the protocol?

-- Hannes