From 06f59e9f5daa06fc4bd51cf4c508b3edd3ed514a Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Fri, 29 Jun 2007 13:40:46 -0400 Subject: Don't fflush(stdout) when it's not helpful 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" Acked-by: Linus Torvalds Signed-off-by: Junio C Hamano --- write_or_die.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) (limited to 'write_or_die.c') diff --git a/write_or_die.c b/write_or_die.c index 5c4bc8515..e125e11d3 100644 --- a/write_or_die.c +++ b/write_or_die.c @@ -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; -- cgit v1.2.1