From 06f59e9f5daa06fc4bd51cf4c508b3edd3ed514a Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Fri, 29 Jun 2007 13:40:46 -0400 Subject: [PATCH] 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 --- Documentation/git.txt | 10 ++++++++++ builtin-blame.c | 1 + builtin-rev-list.c | 2 +- cache.h | 2 ++ log-tree.c | 1 + write_or_die.c | 40 ++++++++++++++++++++++++++++++++++++++++ 6 files changed, 55 insertions(+), 1 deletion(-) diff --git a/Documentation/git.txt b/Documentation/git.txt index 20b5b7bb48..826914837b 100644 --- a/Documentation/git.txt +++ b/Documentation/git.txt @@ -396,6 +396,16 @@ other 'GIT_PAGER':: This environment variable overrides `$PAGER`. +'GIT_FLUSH':: + If this environment variable is set to "1", then commands such + as git-blame (in incremental mode), git-rev-list, git-log, + git-whatchanged, etc., will force a flush of the output stream + after each commit-oriented record have been flushed. If this + variable is set to "0", the output of these commands will be done + using completely buffered I/O. If this environment variable is + not set, git will choose buffered or record-oriented flushing + based on whether stdout appears to be redirected to a file or not. + 'GIT_TRACE':: If this variable is set to "1", "2" or "true" (comparison is case insensitive), git will print `trace:` messages on diff --git a/builtin-blame.c b/builtin-blame.c index f7e2c13885..da23a6f9c9 100644 --- a/builtin-blame.c +++ b/builtin-blame.c @@ -1459,6 +1459,7 @@ static void found_guilty_entry(struct blame_entry *ent) printf("boundary\n"); } write_filename_info(suspect->path); + maybe_flush_or_die(stdout, "stdout"); } } diff --git a/builtin-rev-list.c b/builtin-rev-list.c index 813aadf596..86db8b03fe 100644 --- a/builtin-rev-list.c +++ b/builtin-rev-list.c @@ -100,7 +100,7 @@ static void show_commit(struct commit *commit) printf("%s%c", buf, hdr_termination); free(buf); } - fflush(stdout); + maybe_flush_or_die(stdout, "stdout"); if (commit->parents) { free_commit_list(commit->parents); commit->parents = NULL; diff --git a/cache.h b/cache.h index ed83d92c5a..0525c4ee55 100644 --- a/cache.h +++ b/cache.h @@ -532,6 +532,8 @@ extern char git_default_name[MAX_GITNAME]; extern const char *git_commit_encoding; extern const char *git_log_output_encoding; +/* IO helper functions */ +extern void maybe_flush_or_die(FILE *, const char *); extern int copy_fd(int ifd, int ofd); extern int read_in_full(int fd, void *buf, size_t count); extern int write_in_full(int fd, const void *buf, size_t count); diff --git a/log-tree.c b/log-tree.c index 0cf21bc051..ced3f332ef 100644 --- a/log-tree.c +++ b/log-tree.c @@ -408,5 +408,6 @@ int log_tree_commit(struct rev_info *opt, struct commit *commit) shown = 1; } opt->loginfo = NULL; + maybe_flush_or_die(stdout, "stdout"); return shown; } diff --git a/write_or_die.c b/write_or_die.c index 5c4bc8515a..e125e11d3b 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;