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Don't fflush(stdout) when it's not helpful

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This patch arose from a discussion started by Jim Meyering's patch
whose intention was to provide better diagnostics for failed writes.
Linus proposed a better way to do things, which also had the added
benefit that adding a fflush() to git-log-* operations and incremental
git-blame operations could improve interactive respose time feel, at
the cost of making things a bit slower when we aren't piping the
output to a downstream program.

This patch skips the fflush() calls when stdout is a regular file, or
if the environment variable GIT_FLUSH is set to "0".  This latter can
speed up a command such as:

GIT_FLUSH=0 strace -c -f -e write time git-rev-list HEAD | wc -l

a tiny amount.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Theodore Ts'o
2007-06-29 13:40:46 -04:00
committed by Junio C Hamano
parent ee36856d8c
commit 06f59e9f5d
6 changed files with 55 additions and 1 deletions
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40
write_or_die.c
View File

@ -1,5 +1,45 @@
#include "cache.h"
/*
* Some cases use stdio, but want to flush after the write
* to get error handling (and to get better interactive
* behaviour - not buffering excessively).
*
* Of course, if the flush happened within the write itself,
* we've already lost the error code, and cannot report it any
* more. So we just ignore that case instead (and hope we get
* the right error code on the flush).
*
* If the file handle is stdout, and stdout is a file, then skip the
* flush entirely since it's not needed.
*/
void maybe_flush_or_die(FILE *f, const char *desc)
{
static int skip_stdout_flush = -1;
struct stat st;
char *cp;
if (f == stdout) {
if (skip_stdout_flush < 0) {
cp = getenv("GIT_FLUSH");
if (cp)
skip_stdout_flush = (atoi(cp) == 0);
else if ((fstat(fileno(stdout), &st) == 0) &&
S_ISREG(st.st_mode))
skip_stdout_flush = 1;
else
skip_stdout_flush = 0;
}
if (skip_stdout_flush && !ferror(f))
return;
}
if (fflush(f)) {
if (errno == EPIPE)
exit(0);
die("write failure on %s: %s", desc, strerror(errno));
}
}
int read_in_full(int fd, void *buf, size_t count)
{
char *p = buf;