watch: use EOFpipe to reduce dwaitpid wakeups

It's a bit inefficient to use a pipe, here.  However, using
dwaitpid() on a process that's not expected to exit soon is
also inefficient as it causes excessive wakeups as most of
our inbox-writing code expects synchronous waitpid().

This only affects -watch instances configured for NNTP and IMAP
clients.

1 files changed, 24 insertions, 0 deletions

diff --git a/lib/PublicInbox/EOFpipe.pm b/lib/PublicInbox/EOFpipe.pm
new file mode 100644
index 00000000..489caf82
--- /dev/null
+++ b/lib/PublicInbox/EOFpipe.pm
@@ -0,0 +1,24 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+package PublicInbox::EOFpipe;
+use strict;
+use parent qw(PublicInbox::DS);
+use PublicInbox::Syscall qw(EPOLLIN EPOLLONESHOT);
+
+sub new {
+        my (undef, $rd, $cb, $arg) = @_;
+        my $self = bless {  cb => $cb, arg => $arg }, __PACKAGE__;
+        # 1031: F_SETPIPE_SZ, 4096: page size
+        fcntl($rd, 1031, 4096) if $^O eq 'linux';
+        $self->SUPER::new($rd, EPOLLIN|EPOLLONESHOT);
+}
+
+sub event_step {
+        my ($self) = @_;
+        if ($self->do_read(my $buf, 1) == 0) { # auto-closed
+                $self->{cb}->($self->{arg});
+        }
+}
+
+1;