Re: [PATCH] Use line buffering for standard output

[Anders Melchiorsen <mail@cup.kalibalik.dk>]

Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Sun, 3 Aug 2008, Anders Melchiorsen wrote:
>>
>> By always setting stdout to line buffering, we make the output work
>> identically for all output devices.
>
> Please don't.
>
> This is a huge peformance issue for things like
>
> 	git log -p > file
>
> where we really want it to be fully buffered.
>
> So please just find the place where we do a fork() without flushing
> pending output...

Sure. The sledgehammer approach was partly to get some advice on the
proper solution. I now realize that you have generally been careful
about this, and so a single flush should be enough.

Below are two alternative proposals, one local and one global. Both of
them fix the problem for me, but maybe you were even thinking about a
third place?

For the run-command.c one, I was not sure whether to put it inside or
outside the ifdef, and I also was not sure whether to add it for
start_command(). Not having other testcases, and not knowing Windows,
this is the way it ended up.


Cheers,
Anders.



From: Anders Melchiorsen <mail@cup.kalibalik.dk>
Date: Mon, 4 Aug 2008 00:21:49 +0200
Subject: [PATCH] Flush stdout in init-db

Before this change, clone outputs "Initialized empty ..." twice
if output is piped.

Signed-off-by: Anders Melchiorsen <mail@cup.kalibalik.dk>
---
 builtin-init-db.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/builtin-init-db.c b/builtin-init-db.c
index baf0d09..954c7e9 100644
--- a/builtin-init-db.c
+++ b/builtin-init-db.c
@@ -315,11 +315,13 @@ int init_db(const char *template_dir, unsigned int flags)
 		git_config_set("receive.denyNonFastforwards", "true");
 	}
 
-	if (!(flags & INIT_DB_QUIET))
+	if (!(flags & INIT_DB_QUIET)) {
 		printf("%s%s Git repository in %s/\n",
 		       reinit ? "Reinitialized existing" : "Initialized empty",
 		       shared_repository ? " shared" : "",
 		       get_git_dir());
+		fflush(stdout);
+	}
 
 	return 0;
 }



From: Anders Melchiorsen <mail@cup.kalibalik.dk>
Date: Mon, 4 Aug 2008 00:35:40 +0200
Subject: [PATCH] Flush standard output in start_async

This prevents double output in case stdout is redirected.

Signed-off-by: Anders Melchiorsen <mail@cup.kalibalik.dk>
---
 run-command.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/run-command.c b/run-command.c
index a3b28a6..67be079 100644
--- a/run-command.c
+++ b/run-command.c
@@ -304,6 +304,9 @@ int start_async(struct async *async)
 	async->out = pipe_out[0];
 
 #ifndef __MINGW32__
+	/* Flush output before fork() to avoid cloning the buffer */
+	fflush(stdout);
+
 	async->pid = fork();
 	if (async->pid < 0) {
 		error("fork (async) failed: %s", strerror(errno));