threads / patch / 4191

patchProvide a way to flush git-diff-tree's output

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

## tl;dr

3 messages between May 18, 2006 and May 18, 2006. Diffs are folded; open one to read it.

replies: 2people: 2as markdown or json

Paul Mackerras· May 18, 2006, 06:58 UTC · lore

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>
---

Show changes to diff-tree.c +4 −1

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;
 }

Junio C Hamano· May 18, 2006, 07:24 UTC · re: Paul Mackerras · lore

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

Paul Mackerras <paulus@samba.org> writes:

Show 7 quoted lines

> 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.

Sounds low impact and sane.

I suspect the usual caveat on bidirectional pipe deadlock applies to the caller. Does gitk do that? The current code seems to feed a pre-generated list with "open | cmd <<" construct to the command, so perhaps you are planning to change that?

Paul Mackerras· May 18, 2006, 09:43 UTC · re: Junio C Hamano · lore

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

Junio C Hamano writes:

> Sounds low impact and sane.
> 
> I suspect the usual caveat on bidirectional pipe deadlock
> applies to the caller.  Does gitk do that?  The current code

Gitk will use non-blocking mode on the pipes to/from the git-diff-tree process, so there isn't a possibility of deadlock that I can see.

> seems to feed a pre-generated list with "open | cmd <<"
> construct to the command, so perhaps you are planning to change
> that?

That's for the "Find" function. I'm in the process of adding the code to let users enter a list of paths and have gitk highlight the commits affecting those paths. That will involve a separate invocation of git-diff-tree. To make it responsive, I'm only going to ask git-diff-tree about the commits that are visible on the screen - but I need git-diff-tree to give me an answer quickly, i.e. in less time than a human can perceive.

Thanks, Paul.