Clean up inconsistent use of fflush().

More than twenty years ago (79fcde48b), we hacked the postmaster
to avoid a core-dump on systems that didn't support fflush(NULL).
We've mostly, though not completely, hewed to that rule ever since.
But such systems are surely gone in the wild, so in the spirit of
cleaning out no-longer-needed portability hacks let's get rid of
multiple per-file fflush() calls in favor of using fflush(NULL).

Also, we were fairly inconsistent about whether to fflush() before
popen() and system() calls.  While we've received no bug reports
about that, it seems likely that at least some of these call sites
are at risk of odd behavior, such as error messages appearing in
an unexpected order.  Rather than expend a lot of brain cells
figuring out which places are at hazard, let's just establish a
uniform coding rule that we should fflush(NULL) before these calls.
A no-op fflush() is surely of trivial cost compared to launching
a sub-process via a shell; while if it's not a no-op then we likely
need it.

Discussion: https://postgr.es/m/2923412.1661722825@sss.pgh.pa.us

1 files changed, 8 insertions, 10 deletions

diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index a803355f8ee..7290948eeee 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -263,15 +263,12 @@ stop_postmaster(void)
 		char		buf[MAXPGPATH * 2];
 		int			r;
 
-		/* On Windows, system() seems not to force fflush, so... */
-		fflush(stdout);
-		fflush(stderr);
-
 		snprintf(buf, sizeof(buf),
 				 "\"%s%spg_ctl\" stop -D \"%s/data\" -s",
 				 bindir ? bindir : "",
 				 bindir ? "/" : "",
 				 temp_instance);
+		fflush(NULL);
 		r = system(buf);
 		if (r != 0)
 		{
@@ -1029,6 +1026,7 @@ psql_end_command(StringInfo buf, const char *database)
 					 database);
 
 	/* And now we can execute the shell command */
+	fflush(NULL);
 	if (system(buf->data) != 0)
 	{
 		/* psql probably already reported the error */
@@ -1063,13 +1061,9 @@ spawn_process(const char *cmdline)
 	pid_t		pid;
 
 	/*
-	 * Must flush I/O buffers before fork.  Ideally we'd use fflush(NULL) here
-	 * ... does anyone still care about systems where that doesn't work?
+	 * Must flush I/O buffers before fork.
 	 */
-	fflush(stdout);
-	fflush(stderr);
-	if (logfile)
-		fflush(logfile);
+	fflush(NULL);
 
 #ifdef EXEC_BACKEND
 	pg_disable_aslr();
@@ -1247,6 +1241,7 @@ run_diff(const char *cmd, const char *filename)
 {
 	int			r;
 
+	fflush(NULL);
 	r = system(cmd);
 	if (!WIFEXITED(r) || WEXITSTATUS(r) > 1)
 	{
@@ -2264,6 +2259,7 @@ regression_main(int argc, char *argv[],
 				 debug ? " --debug" : "",
 				 nolocale ? " --no-locale" : "",
 				 outputdir);
+		fflush(NULL);
 		if (system(buf))
 		{
 			fprintf(stderr, _("\n%s: initdb failed\nExamine %s/log/initdb.log for the reason.\nCommand was: %s\n"), progname, outputdir, buf);
@@ -2335,6 +2331,7 @@ regression_main(int argc, char *argv[],
 
 		for (i = 0; i < 16; i++)
 		{
+			fflush(NULL);
 			if (system(buf2) == 0)
 			{
 				char		s[16];
@@ -2398,6 +2395,7 @@ regression_main(int argc, char *argv[],
 		for (i = 0; i < wait_seconds; i++)
 		{
 			/* Done if psql succeeds */
+			fflush(NULL);
 			if (system(buf2) == 0)
 				break;