lei: avoid deadlock on inotify/EVFILT_VNODE wakeups

Enqueuing "note-event" requests from the DS event loop must
not wait on workers being able to drain the queue quickly
enough.  Thus we make the SOCK_SEQPACKET writes nonblocking
and rely on the lei-daemon event loop to enqueue writes.

This is a unique problem for "note-event" since it reuses
workers in between commands, while most lei commands currently
fork off new workers.

1 files changed, 49 insertions, 0 deletions

diff --git a/lib/PublicInbox/WQBlocked.pm b/lib/PublicInbox/WQBlocked.pm
new file mode 100644
index 00000000..fbb43600
--- /dev/null
+++ b/lib/PublicInbox/WQBlocked.pm
@@ -0,0 +1,49 @@
+# Copyright (C) all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# non-blocking workqueues, currently used by LeiNoteEvent to track renames
+package PublicInbox::WQBlocked;
+use v5.12;
+use parent qw(PublicInbox::DS);
+use PublicInbox::Syscall qw(EPOLLOUT EPOLLONESHOT);
+use PublicInbox::IPC;
+use Carp ();
+use Socket qw(MSG_EOR);
+
+sub new {
+        my ($cls, $wq, $buf) = @_;
+        my $self = bless { msgq => [$buf], }, $cls;
+        $wq->{wqb} = $self->SUPER::new($wq->{-wq_s1}, EPOLLOUT|EPOLLONESHOT);
+}
+
+sub flush_send {
+        my ($self) = @_;
+        push(@{$self->{msgq}}, $_[1]) if defined($_[1]);
+        while (defined(my $buf = shift @{$self->{msgq}})) {
+                if (ref($buf) eq 'CODE') {
+                        $buf->($self); # could be \&PublicInbox::DS::close
+                } else {
+                        my $wq_s1 = $self->{sock};
+                        my $n = $PublicInbox::IPC::send_cmd->($wq_s1, [], $buf,
+                                                                MSG_EOR);
+                        next if defined($n);
+                        Carp::croak("sendmsg: $!") unless $!{EAGAIN};
+                        PublicInbox::DS::epwait($wq_s1, EPOLLOUT|EPOLLONESHOT);
+                        unshift @{$self->{msgq}}, $buf;
+                        last; # wait for ->event_step
+                }
+        }
+}
+
+sub enq_close { flush_send($_[0], $_[0]->can('close')) }
+
+sub event_step { # called on EPOLLOUT wakeup
+        my ($self) = @_;
+        eval { flush_send($self) } if $self->{sock};
+        if ($@) {
+                warn $@;
+                $self->close;
+        }
+}
+
+1;