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From: Eric Wong <e@80x24.org>
To: meta@public-inbox.org
Subject: [PATCH 2/3] script/lei: handle SIGTSTP and SIGCONT
Date: Tue, 21 Sep 2021 09:29:44 +0000
Message-Id: <20210921092945.23916-3-e@80x24.org>
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Sometimes it's useful to pause an expensive query or
refresh-mail-sync to do something else.  While lei-daemon and
lei/store can't be paused since they're shared across clients,
per-invocation WQ workers can be paused safely using the
unblockable SIGSTOP.

While we're at it, drop the ETOOMANYREFS hint since it
hasn't been a problem since we drastically reduced FD passing
early in development.
---
 lib/PublicInbox/LEI.pm | 18 ++++++++++++------
 script/lei             |  9 ++++-----
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index f94bfa45..2df1f326 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -1118,23 +1118,28 @@ sub dclose {
 sub event_step {
 	my ($self) = @_;
 	local %ENV = %{$self->{env}};
-	my $sock = $self->{sock};
 	local $current_lei = $self;
 	eval {
-		while (my @fds = $recv_cmd->($sock, my $buf, 4096)) {
+		my $buf;
+		while (my @fds = $recv_cmd->($self->{sock}, $buf, 4096)) {
 			if (scalar(@fds) == 1 && !defined($fds[0])) {
 				return if $! == EAGAIN;
 				next if $! == EINTR;
 				last if $! == ECONNRESET;
 				die "recvmsg: $!";
 			}
-			for my $fd (@fds) {
-				open my $rfh, '+<&=', $fd;
+			for (@fds) { open my $rfh, '+<&=', $_ }
+		}
+		if ($buf eq '') {
+			_drop_wq($self); # EOF, client disconnected
+			dclose($self);
+		} elsif ($buf =~ /\A(STOP|CONT)\z/) {
+			for my $wq (grep(defined, @$self{@WQ_KEYS})) {
+				$wq->wq_kill($buf) or $wq->wq_kill_old($buf);
 			}
+		} else {
 			die "unrecognized client signal: $buf";
 		}
-		_drop_wq($self); # EOF, client disconnected
-		dclose($self);
 	};
 	if (my $err = $@) {
 		eval { $self->fail($err) };
@@ -1146,6 +1151,7 @@ sub event_step_init {
 	my ($self) = @_;
 	my $sock = $self->{sock} or return;
 	$self->{-event_init_done} //= do { # persist til $ops done
+		$sock->blocking(0);
 		$self->SUPER::new($sock, EPOLLIN|EPOLLET);
 		$sock;
 	};
diff --git a/script/lei b/script/lei
index 591013e3..399296ba 100755
--- a/script/lei
+++ b/script/lei
@@ -106,11 +106,10 @@ open my $dh, '<', '.' or die "open(.) $!";
 my $buf = join("\0", scalar(@ARGV), @ARGV);
 while (my ($k, $v) = each %ENV) { $buf .= "\0$k=$v" }
 $buf .= "\0\0";
-my $n = $send_cmd->($sock, [0, 1, 2, fileno($dh)], $buf, MSG_EOR);
-if (!$n) {
-	die "sendmsg: $! (check RLIMIT_NOFILE)\n" if $!{ETOOMANYREFS};
-	die "sendmsg: $!\n";
-}
+$send_cmd->($sock, [0, 1, 2, fileno($dh)], $buf, MSG_EOR) or die "sendmsg: $!";
+$SIG{TSTP} = sub { $send_cmd->($sock, [], 'STOP', MSG_EOR); kill 'STOP', $$ };
+$SIG{CONT} = sub { $send_cmd->($sock, [], 'CONT', MSG_EOR) };
+
 my $x_it_code = 0;
 while (1) {
 	my (@fds) = $recv_cmd->($sock, my $buf, 4096 * 33);