Subject: Re: [PATCH v2 5/8] progress.c: stop eagerly fflush(stderr) when not a terminal

From: Emily Shaffer <[email-masked]>
Date: Thu, 7 Oct 2021 20:59:49 -0700

On Tue, Sep 21, 2021 at 01:09:26AM +0200, Ævar Arnfjörð Bjarmason wrote:
> 
> It's the clear intention of the combination of 137a0d0ef56 (Flush
> progress message buffer in display()., 2007-11-19) and
> 85cb8906f0e (progress: no progress in background, 2015-04-13) to call
> fflush(stderr) when we have a stderr in the foreground, but we ended
> up always calling fflush(stderr) seemingly by omission. Let's not.
> 
> Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
> ---
>  progress.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/progress.c b/progress.c
> index 7fcc513717a..1fade5808de 100644
> --- a/progress.c
> +++ b/progress.c
> @@ -91,7 +91,8 @@ static void display(struct progress *progress, uint64_t n, const char *done)
>  	}
>  
>  	if (show_update) {
> -		if (is_foreground_fd(fileno(stderr)) || done) {
> +		int stderr_is_foreground_fd = is_foreground_fd(fileno(stderr));
> +		if (stderr_is_foreground_fd || done) {
>  			const char *eol = done ? done : "\r";
>  			size_t clear_len = counters_sb->len < last_count_len ?
>  					last_count_len - counters_sb->len + 1 :
> @@ -115,7 +116,8 @@ static void display(struct progress *progress, uint64_t n, const char *done)
>  				fprintf(stderr, "%s: %s%*s", progress->title,
>  					counters_sb->buf, (int) clear_len, eol);
>  			}
> -			fflush(stderr);
> +			if (stderr_is_foreground_fd)
> +				fflush(stderr);

Looks like a straightforward refactor, although I wonder what's the
difference between is_foreground_fd(fileno(stderr)) and isatty() in
practice.

Reviewed-by: Emily Shaffer <[email-masked]>

>  		}
>  		progress_update = 0;
>  	}
> -- 
> 2.33.0.1098.gf02a64c1a2d