[PATCH 2/2] t/httpd-unix: reliability for non-signalfd/EVFILT_SIGNAL

[Eric Wong <e@yhbt.net>]

Perl seems unable to detect a pending signal (`PL_sig_pending' flag)
even in a sleep(1) loop which wakes up every second.

The (SIGTTOU|SIGUSR2|SIGQUIT) signal itself in the
`PL_psig_pend[sig]' array is not lost, so we can send SIGCHLD
to the process to force the `PL_sig_pending' into being set,
again.

I tested this commit in a loop with the following patch on a
Debian GNU/Linux system to disable signalfd use:

	diff --git a/lib/PublicInbox/Sigfd.pm b/lib/PublicInbox/Sigfd.pm
	index f500902e..597b40d1 100644
	--- a/lib/PublicInbox/Sigfd.pm
	+++ b/lib/PublicInbox/Sigfd.pm
	@@ -12,6 +12,7 @@ use IO::Handle ();
	 # are available.
	 sub new {
		my ($class, $sig, $flags) = @_;
	+	return;
		my $self = fields::new($class);
		my %signo = map {;
			my $cb = $sig->{$_};
---
 t/httpd-unix.t | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/t/httpd-unix.t b/t/httpd-unix.t
index 7ebc3464..3bfded0c 100644
--- a/t/httpd-unix.t
+++ b/t/httpd-unix.t
@@ -81,13 +81,27 @@ check_sock($unix);
 	ok(-S $unix, 'unix socket still exists');
 }
 
+# Perl can delay signal dispatches due to races, so we repeatedly
+# poke a process with an innocuous signal (SIGCHLD) when signalfd(2)
+# (or EVFILT_SIGNAL) is missing
+my $sig_poke;
+if (my $sigfd = PublicInbox::Sigfd->new({}, 0)) {
+	$sig_poke = sub {}; # noop, we've got signalfd or EVFILT_SIGNAL
+} else {
+	$sig_poke = sub {
+		my $pid = shift;
+		kill('CHLD', $pid);
+	};
+}
+
 sub delay_until {
 	my $cond = shift;
-	for (1..1000) {
+	my $end = time + 30;
+	do {
 		return if $cond->();
 		select undef, undef, undef, 0.012;
-	}
-	Carp::croak('condition failed');
+	} until (time > $end);
+	Carp::confess('condition failed');
 }
 
 SKIP: {
@@ -133,19 +147,23 @@ SKIP: {
 
 	kill('USR2', $pid) or die "USR2 failed: $!";
 	delay_until(sub {
+		$sig_poke->($pid);
 		$pid != (eval { $read_pid->($pid_file) } // $pid)
 	});
 	my $new_pid = $read_pid->($pid_file);
 	isnt($new_pid, $pid, 'new child started');
+	ok($new_pid > 0, '$new_pid valid');
 	delay_until(sub { -s "$pid_file.oldbin" });
 	my $old_pid = $read_pid->("$pid_file.oldbin");
 	is($old_pid, $pid, '.oldbin pid file written');
+	ok($old_pid > 0, '$old_pid valid');
 
 	check_sock($unix); # ensures $new_pid is ready to receive signals
 
 	# first, back out of the upgrade
 	kill('QUIT', $new_pid) or die "kill new PID failed: $!";
 	delay_until(sub {
+		$sig_poke->($new_pid);
 		$pid == (eval { $read_pid->($pid_file) } // 0)
 	});
 	is($read_pid->($pid_file), $pid, 'old PID file restored');