Subject: Re: [PATCH 2/5] progress: return early when in the background

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Mon, 25 Mar 2019 12:08:47 +0100

On Mon, Mar 25 2019, SZEDER Gábor wrote:

> When a git process runs in the background, it doesn't display
> progress, only the final "done" line [1].  The condition to check that
> are a bit too deep in the display() function, and thus it calculates
> the progress percentage even when no progress will be displayed
> anyway.
>
> Restructure the display() function to return early when we are in the
> background, which prevents the unnecessary progress percentae
> calculation, and make the function look a bit better by losing one
> level of indentation.
>
> [1] 85cb8906f0 (progress: no progress in background, 2015-04-13)

CC-ing the author of that patch.

> Signed-off-by: SZEDER Gábor <[email-masked]>
> ---
>  progress.c | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/progress.c b/progress.c
> index 02a20e7d58..b57c0dae16 100644
> --- a/progress.c
> +++ b/progress.c
> @@ -86,28 +86,30 @@ static void display(struct progress *progress, uint64_t n, const char *done)
>  		return;
>
>  	progress->last_value = n;
> +
> +	if (!is_foreground_fd(fileno(stderr)) && !done) {
> +		progress_update = 0;
> +		return;
> +	}
> +
>  	tp = (progress->throughput) ? progress->throughput->display.buf : "";
>  	eol = done ? done : "   \r";
>  	if (progress->total) {
>  		unsigned percent = n * 100 / progress->total;
>  		if (percent != progress->last_percent || progress_update) {
>  			progress->last_percent = percent;
> -			if (is_foreground_fd(fileno(stderr)) || done) {
> -				fprintf(stderr, "%s: %3u%% (%"PRIuMAX"/%"PRIuMAX")%s%s",
> -					progress->title, percent,
> -					(uintmax_t)n, (uintmax_t)progress->total,
> -					tp, eol);
> -				fflush(stderr);
> -			}
> +			fprintf(stderr, "%s: %3u%% (%"PRIuMAX"/%"PRIuMAX")%s%s",
> +				progress->title, percent,
> +				(uintmax_t)n, (uintmax_t)progress->total,
> +				tp, eol);
> +			fflush(stderr);
>  			progress_update = 0;
>  			return;
>  		}
>  	} else if (progress_update) {
> -		if (is_foreground_fd(fileno(stderr)) || done) {
> -			fprintf(stderr, "%s: %"PRIuMAX"%s%s",
> -				progress->title, (uintmax_t)n, tp, eol);
> -			fflush(stderr);
> -		}
> +		fprintf(stderr, "%s: %"PRIuMAX"%s%s",
> +			progress->title, (uintmax_t)n, tp, eol);
> +		fflush(stderr);
>  		progress_update = 0;
>  		return;
>  	}

This patch looks good, just notes for potential follow-up:

 * Is the "is_foreground_fd(fileno(stderr))" case worth moving into
   start_progress_delay() & setting a variable? It's a few C lib calls &
   potential syscall (getpid(...)).

 * Is that "|| done" part in the "progress_update" case something that
   needs to happen? I.e. can we entirely skip the "setup signal handler"
   part in start_progress_delay() if we detect that we're not in the
   foreground, and then rely on the stop_progress() call to print the
   "done"?

   Although we set "progress_update = 1" in stop_progress_msg(), so it's
   not *just* the signal handler but also us "faking" it, and we'd still
   need to stash away "progress->last_value = n" in display() in that
   backgrounding case.

   So maybe it's as simple as it's going to get.