[PATCH v2] reduce progress updates in background

[Luke Mewburn <luke@mewburn.net>]

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Updated patch where is_foreground_fd() is only called in display()
just before the output is to be displayed.

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From d87997509fc631b8cdc7db63f289102d6ddfe933 Mon Sep 17 00:00:00 2001
From: Luke Mewburn <luke@mewburn.net>
Date: Mon, 13 Apr 2015 23:30:51 +1000
Subject: [PATCH] progress: no progress in background

Disable the display of the progress if stderr is not the
current foreground process.
Still display the final result when done.

Signed-off-by: Luke Mewburn <luke@mewburn.net>
---
 progress.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/progress.c b/progress.c
index 412e6b1..43d9228 100644
--- a/progress.c
+++ b/progress.c
@@ -72,6 +72,11 @@ static void clear_progress_signal(void)
 	progress_update = 0;
 }
 
+static int is_foreground_fd(int fd)
+{
+	return getpgid(0) == tcgetpgrp(fd);
+}
+
 static int display(struct progress *progress, unsigned n, const char *done)
 {
 	const char *eol, *tp;
@@ -98,16 +103,21 @@ static int display(struct progress *progress, unsigned n, const char *done)
 		unsigned percent = n * 100 / progress->total;
 		if (percent != progress->last_percent || progress_update) {
 			progress->last_percent = percent;
-			fprintf(stderr, "%s: %3u%% (%u/%u)%s%s",
-				progress->title, percent, n,
-				progress->total, tp, eol);
-			fflush(stderr);
+			if (is_foreground_fd(fileno(stderr)) || done) {
+				fprintf(stderr, "%s: %3u%% (%u/%u)%s%s",
+					progress->title, percent, n,
+					progress->total, tp, eol);
+				fflush(stderr);
+			}
 			progress_update = 0;
 			return 1;
 		}
 	} else if (progress_update) {
-		fprintf(stderr, "%s: %u%s%s", progress->title, n, tp, eol);
-		fflush(stderr);
+		if (is_foreground_fd(fileno(stderr)) || done) {
+			fprintf(stderr, "%s: %u%s%s",
+				progress->title, n, tp, eol);
+			fflush(stderr);
+		}
 		progress_update = 0;
 		return 1;
 	}
-- 
2.3.5.1.gd879975


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