[PATCH] Provide a way to flush git-diff-tree's output

From: Paul Mackerras <paulus@samba.org>
Date: May 18, 2006, 06:58 UTC
Message-ID: <17516.6955.282732.460675@cargo.ozlabs.ibm.com>

Gitk wants to use git-diff-tree as a filter to tell it which ids from a given list affect a set of files or directories. We don't want to fork and exec a new git-diff-tree process for each batch of ids, since there could be a lot of relatively small batches. For example, a batch could contain as many ids as fit in gitk's headline display window, i.e. 20 or so, and we would be processing a new batch every time the user scrolls that window.

The --stdin flag to git-diff-tree is suitable for this, but the main difficulty is that the output of git-diff-tree gets buffered and doesn't get sent until the buffer is full.

This provides a way to get git-diff-tree to flush its output buffers. If a blank line is supplied on git-diff-tree's standard input, it will flush its output buffers and then accept further input.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---

diff --git a/diff-tree.c b/diff-tree.c
index 7207867..69bb74b 100644
--- a/diff-tree.c
+++ b/diff-tree.c
@@ -138,7 +138,10 @@ int main(int argc, const char **argv)
 		opt->diffopt.setup |= (DIFF_SETUP_USE_SIZE_CACHE |
 				       DIFF_SETUP_USE_CACHE);
 	while (fgets(line, sizeof(line), stdin))
-		diff_tree_stdin(line);
+		if (line[0] == '\n')
+			fflush(stdout);
+		else
+			diff_tree_stdin(line);
 
 	return 0;
 }