parentpipe: document and use one-shot wakeups

The master process only dies once and we close ourselves right
away.  So it doesn't matter if it's level-triggered or
edge-triggered, actually, but one-shot is most consistent with
our use and keeps the kernel from doing extra work.

diff --git a/lib/PublicInbox/ParentPipe.pm b/lib/PublicInbox/ParentPipe.pm
index ccc0815ea46d5400ba591d2457aba220a9b2c2f1..6ef51c1adbd536527abe71598b899d9783d06220 100644 (file)
--- a/lib/PublicInbox/ParentPipe.pm
+++ b/lib/PublicInbox/ParentPipe.pm
@@ -1,20 +1,24 @@
 # Copyright (C) 2016-2018 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
-# only for PublicInbox::Daemon
+
+# only for PublicInbox::Daemon, allows worker processes to be
+# notified if the master process dies.
 package PublicInbox::ParentPipe;
 use strict;
 use warnings;
 use base qw(PublicInbox::DS);
 use fields qw(cb);
+use PublicInbox::Syscall qw(EPOLLIN EPOLLONESHOT);
 
 sub new ($$$) {
-       my ($class, $pipe, $cb) = @_;
+       my ($class, $pipe, $worker_quit) = @_;
        my $self = fields::new($class);
-       $self->SUPER::new($pipe, PublicInbox::DS::EPOLLIN());
-       $self->{cb} = $cb;
+       $self->SUPER::new($pipe, EPOLLIN|EPOLLONESHOT);
+       $self->{cb} = $worker_quit;
        $self;
 }
 
+# master process died, time to call worker_quit ourselves
 sub event_step { $_[0]->{cb}->($_[0]) }
 
 1;