[PATCH] daemon: re-enable SIGWINCH without setsid

[PATCH] daemon: re-enable SIGWINCH without setsid

[Eric Wong]

This allows systemd users to use SIGWINCH to temporarily
(and gracefully) stop an instance of a service without
doing a code reload to bring it back up:

	# start temporary new service code
	systemctl start public-inbox-nntpd@2.service

	# momentarily paralyze original service
	systemctl kill -s WINCH public-inbox-nntpd@1.service

	if new_code_at_2_sucks
	then
		# restart original workers
		systemctl kill -s HUP public-inbox-nntpd@1.service
	else # new is better than old, replace original instance
		systemctl restart public-inbox-nntpd@1.service
	fi

	# cleanup the temporary service
	systemctl stop public-inbox-nntpd@2.service

This partially reverts commit 73d274e83b7d300f31e0cc1ceeacbf73c6c2a1e4
("daemon: disable SIGWINCH unless explicitly daemonized")
---
 lib/PublicInbox/Daemon.pm | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/PublicInbox/Daemon.pm b/lib/PublicInbox/Daemon.pm
index 7849f9c..9125584 100644
--- a/lib/PublicInbox/Daemon.pm
+++ b/lib/PublicInbox/Daemon.pm
@@ -112,7 +112,6 @@ sub daemonize () {
 	check_absolute('pid-file', $pid_file);
 
 	chdir '/' or die "chdir failed: $!";
-	open(STDIN, '+<', '/dev/null') or die "redirect stdin failed: $!";
 
 	return unless (defined $pid_file || defined $group || defined $user
 			|| $daemonize);
@@ -145,6 +144,8 @@ sub daemonize () {
 		die "could not fork: $!\n" unless defined $pid;
 		exit if $pid;
 
+		open(STDIN, '+<', '/dev/null') or
+					die "redirect stdin failed: $!\n";
 		open STDOUT, '>&STDIN' or die "redirect stdout failed: $!\n";
 		open STDERR, '>&STDIN' or die "redirect stderr failed: $!\n";
 		POSIX::setsid();
@@ -376,12 +377,12 @@ sub master_loop {
 				exit if $quit++;
 				kill_workers($s);
 			} elsif ($s eq 'WINCH') {
-				if ($daemonize) {
-					$worker_processes = 0;
-				} else {
+				if (-t STDIN || -t STDOUT || -t STDERR) {
 					warn
 "ignoring SIGWINCH since we are not daemonized\n";
 					$SIG{WINCH} = 'IGNORE';
+				} else {
+					$worker_processes = 0;
 				}
 			} elsif ($s eq 'HUP') {
 				$worker_processes = $set_workers;
-- 
EW