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.

diff --git a/MANIFEST b/MANIFEST
index f090175e7270a57e89839981748aa3b5d12c2521..0b3835d8a1aa0c4d28ebd91249abc8e447d0624e 100644 (file)
--- a/MANIFEST
+++ b/MANIFEST
@@ -114,6 +114,7 @@ lib/PublicInbox/DSPoll.pm
 lib/PublicInbox/Daemon.pm
 lib/PublicInbox/DirIdle.pm
 lib/PublicInbox/DummyInbox.pm
+lib/PublicInbox/EOFpipe.pm
 lib/PublicInbox/Emergency.pm
 lib/PublicInbox/Eml.pm
 lib/PublicInbox/EmlContentFoo.pm

diff --git a/lib/PublicInbox/EOFpipe.pm b/lib/PublicInbox/EOFpipe.pm
new file mode 100644 (file)
index 0000000..489caf8
--- /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;

diff --git a/lib/PublicInbox/Watch.pm b/lib/PublicInbox/Watch.pm
index db8d03964cddd1c4055ea6682ba70b5138c37031..17786377ba8127fe7744acc14216f873ec71edf7 100644 (file)
--- a/lib/PublicInbox/Watch.pm
+++ b/lib/PublicInbox/Watch.pm
@@ -14,7 +14,8 @@ use PublicInbox::Sigfd;
 use PublicInbox::DS qw(now);
 use PublicInbox::MID qw(mids);
 use PublicInbox::ContentHash qw(content_hash);
-use POSIX qw(_exit);
+use PublicInbox::EOFpipe;
+use POSIX qw(_exit WNOHANG);
 
 sub compile_watchheaders ($) {
        my ($ibx) = @_;
@@ -611,17 +612,30 @@ sub imap_idle_reap { # PublicInbox::DS::dwaitpid callback
                                \&imap_idle_requeue, [ $self, $url_intvl ]);
 }
 
+sub reap { # callback for EOFpipe
+       my ($pid, $cb, $self) = @{$_[0]};
+       my $ret = waitpid($pid, 0);
+       if ($ret == $pid) {
+               $cb->($self, $pid); # poll_fetch_reap || imap_idle_reap
+       } else {
+               warn "W: waitpid($pid) => ", $ret // "($!)", "\n";
+       }
+}
+
 sub imap_idle_fork ($$) {
        my ($self, $url_intvl) = @_;
        my ($url, $intvl) = @$url_intvl;
+       pipe(my ($r, $w)) or die "pipe: $!";
        defined(my $pid = fork) or die "fork: $!";
        if ($pid == 0) {
+               close $r;
                watch_atfork_child($self);
                watch_imap_idle_1($self, $url, $intvl);
+               close $w;
                _exit(0);
        }
        $self->{idle_pids}->{$pid} = $url_intvl;
-       PublicInbox::DS::dwaitpid($pid, \&imap_idle_reap, $self);
+       PublicInbox::EOFpipe->new($r, \&reap, [$pid, \&imap_idle_reap, $self]);
 }
 
 sub event_step {
@@ -689,24 +703,27 @@ sub watch_nntp_fetch_all ($$) {
 sub poll_fetch_fork ($) { # DS::add_timer callback
        my ($self, $intvl, $urls) = @{$_[0]};
        return if $self->{quit};
+       pipe(my ($r, $w)) or die "pipe: $!";
        my $oldset = watch_atfork_parent($self);
        my $pid = fork;
        if (defined($pid) && $pid == 0) {
+               close $r;
                watch_atfork_child($self);
                if ($urls->[0] =~ m!\Aimaps?://!i) {
                        watch_imap_fetch_all($self, $urls);
                } else {
                        watch_nntp_fetch_all($self, $urls);
                }
+               close $w;
                _exit(0);
        }
        PublicInbox::Sigfd::sig_setmask($oldset);
        die "fork: $!"  unless defined $pid;
        $self->{poll_pids}->{$pid} = [ $intvl, $urls ];
-       PublicInbox::DS::dwaitpid($pid, \&poll_fetch_reap, $self);
+       PublicInbox::EOFpipe->new($r, \&reap, [$pid, \&poll_fetch_reap, $self]);
 }
 
-sub poll_fetch_reap { # PublicInbox::DS::dwaitpid callback
+sub poll_fetch_reap {
        my ($self, $pid) = @_;
        my $intvl_urls = delete $self->{poll_pids}->{$pid} or
                die "BUG: PID=$pid (unknown) reaped: \$?=$?\n";