favor poll(2) for most daemons

public-inbox-watch, lei-daemon, the master process of
public-inbox-(netd|httpd|imapd|nntpd|pop3d),
and the (mostly) Perl implementation of XapHelper do not
have many FDs to watch so epoll|kqueue end up being overkill.

Of course, *BSDs already have separate kqueue FDs emulating
signalfd and/or inotify, even.

In other words, only the worker processes of
public-inbox-(netd|httpd|imapd|nntpd|pop3d) are expected
to see C10K (or C100K) types of traffic where epoll|kqueue
shine.

Perhaps lei could benefit from epoll/kqueue on some virtual users
IMAP/JMAP system one day; as could -watch with many IMAP IDLE
folders; but we'll probably add a knob if/when it comes to that.

3 files changed, 32 insertions, 11 deletions

diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index 9300ac77..f2b14799 100644
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -31,6 +31,7 @@ use Scalar::Util qw(blessed);
 use PublicInbox::Syscall qw(%SIGNUM
         EPOLLIN EPOLLOUT EPOLLONESHOT EPOLLEXCLUSIVE);
 use PublicInbox::Tmpfile;
+use PublicInbox::DSPoll;
 use Errno qw(EAGAIN EINVAL ECHILD EINTR);
 use Carp qw(carp croak);
 our @EXPORT_OK = qw(now msg_more awaitpid add_timer add_uniq_timer);
@@ -42,7 +43,7 @@ my $reap_armed;
 my $ToClose; # sockets to close when event loop is done
 our (
      %DescriptorMap,             # fd (num) -> PublicInbox::DS object
-     $Epoll,  # global Epoll, DSPoll, or DSKQXS ref
+     $Poller, # global Epoll, DSPoll, or DSKQXS ref
 
      @post_loop_do,              # subref + args to call at the end of each loop
 
@@ -75,13 +76,14 @@ sub Reset {
                 my @q = delete @Stack{keys %Stack};
                 for my $q (@q) { @$q = () }
                 $AWAIT_PIDS = $nextq = $ToClose = undef;
-                $Epoll = undef; # may call DSKQXS::DESTROY
+                $Poller = undef; # may call DSKQXS::DESTROY
         } while (@Timers || keys(%Stack) || $nextq || $AWAIT_PIDS ||
                 $ToClose || keys(%DescriptorMap) ||
                 @post_loop_do || keys(%UniqTimer));
 
         $reap_armed = undef;
         $LoopTimeout = -1;  # no timeout by default
+        $Poller = PublicInbox::DSPoll->new;
 }
 
 =head2 C<< CLASS->SetLoopTimeout( $timeout ) >>
@@ -123,7 +125,7 @@ sub add_uniq_timer { # ($name, $secs, $coderef, @args) = @_;
         $UniqTimer{$_[0]} //= _add_named_timer(@_);
 }
 
-# caller sets return value to $Epoll
+# caller sets return value to $Poller
 sub _InitPoller () {
         my @try = ($^O eq 'linux' ? 'Epoll' : 'DSKQXS');
         my $cls;
@@ -269,7 +271,7 @@ sub unblockset ($) { sigset_prep $_[0], 'emptyset', 'addset' }
 # C<post_loop_do> for how to exit the loop.
 sub event_loop (;$$) {
         my ($sig, $oldset) = @_;
-        $Epoll //= _InitPoller();
+        $Poller //= _InitPoller();
         require PublicInbox::Sigfd if $sig;
         my $sigfd = $sig ? PublicInbox::Sigfd->new($sig) : undef;
         if ($sigfd && $sigfd->{is_kq}) {
@@ -298,7 +300,7 @@ sub event_loop (;$$) {
                 my $timeout = RunTimers();
 
                 # get up to 1000 events
-                $Epoll->ep_wait(1000, $timeout, \@events);
+                $Poller->ep_wait(1000, $timeout, \@events);
                 for my $fd (@events) {
                         # it's possible epoll_wait returned many events,
                         # including some at the end that ones in the front
@@ -334,9 +336,9 @@ sub new {
     $self->{sock} = $sock;
     my $fd = fileno($sock);
 
-    $Epoll //= _InitPoller();
+    $Poller //= _InitPoller();
 retry:
-    if ($Epoll->ep_add($sock, $ev)) {
+    if ($Poller->ep_add($sock, $ev)) {
         if ($! == EINVAL && ($ev & EPOLLEXCLUSIVE)) {
             $ev &= ~EPOLLEXCLUSIVE;
             goto retry;
@@ -390,7 +392,7 @@ sub close {
 
     # if we're using epoll, we have to remove this from our epoll fd so we stop getting
     # notifications about it
-    $Epoll->ep_del($sock) and croak("EPOLL_CTL_DEL($self/$sock): $!");
+    $Poller->ep_del($sock) and croak("EPOLL_CTL_DEL($self/$sock): $!");
 
     # we explicitly don't delete from DescriptorMap here until we
     # actually close the socket, as we might be in the middle of
@@ -609,7 +611,7 @@ sub msg_more ($$) {
 
 sub epwait ($$) {
         my ($io, $ev) = @_;
-        $Epoll->ep_mod($io, $ev) and croak("EPOLL_CTL_MOD($io): $!");
+        $Poller->ep_mod($io, $ev) and croak("EPOLL_CTL_MOD($io): $!");
 }
 
 # return true if complete, false if incomplete (or failure)
diff --git a/lib/PublicInbox/Daemon.pm b/lib/PublicInbox/Daemon.pm
index 222093bc..07883153 100644
--- a/lib/PublicInbox/Daemon.pm
+++ b/lib/PublicInbox/Daemon.pm
@@ -556,6 +556,7 @@ sub start_worker ($) {
         } elsif ($pid == 0) {
                 undef %WORKERS;
                 PublicInbox::DS::Reset();
+                local $PublicInbox::DS::Poller; # allow epoll/kqueue
                 srand($seed);
                 eval { Net::SSLeay::randomize() };
                 $set_user->() if $set_user;
@@ -677,6 +678,7 @@ sub daemon_loop () {
                 $WORKER_SIG{USR2} = sub { worker_quit() if upgrade() };
                 $refresh->();
         }
+        local $PublicInbox::DS::Poller; # allow epoll/kqueue
         worker_loop();
 }
 
diff --git a/lib/PublicInbox/TestCommon.pm b/lib/PublicInbox/TestCommon.pm
index b7f1eb57..17057e18 100644
--- a/lib/PublicInbox/TestCommon.pm
+++ b/lib/PublicInbox/TestCommon.pm
@@ -25,7 +25,7 @@ BEGIN {
                 create_coderepo no_scm_rights
                 tcp_host_port test_lei lei lei_ok $lei_out $lei_err $lei_opt
                 test_httpd xbail require_cmd is_xdeeply tail_f
-                ignore_inline_c_missing);
+                ignore_inline_c_missing no_pollerfd);
         require Test::More;
         my @methods = grep(!/\W/, @Test::More::EXPORT);
         eval(join('', map { "*$_=\\&Test::More::$_;" } @methods));
@@ -843,7 +843,24 @@ sub test_httpd ($$;$$) {
         }
 };
 
-
+sub no_pollerfd ($) {
+        my ($pid) = @_;
+        my ($re, @cmd);
+        $^O eq 'linux' and
+                ($re, @cmd) = (qr/\Q[eventpoll]\E/, qw(lsof -p), $pid);
+        # n.b. *BSDs uses kqueue to emulate signalfd and/or inotify,
+        # and we can't distinguish which is which easily.
+        SKIP: {
+                (@cmd && $re) or
+                        skip 'open poller test is Linux-only', 1;
+                my $bin = require_cmd($cmd[0], 1) or skip "$cmd[0] missing", 1;
+                $cmd[0] = $bin;
+                my @of = xqx(\@cmd, {}, {2 => \(my $e)});
+                my $err = $?;
+                skip "$bin broken? (\$?=$err) ($e)", 1 if $err;
+                is(grep(/$re/, @of), 0, "no $re FDs") or diag explain(\@of);
+        }
+}
 package PublicInbox::TestCommon::InboxWakeup;
 use strict;
 sub on_inbox_unlock { ${$_[0]}->($_[1]) }