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.

1 files changed, 19 insertions, 2 deletions

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]) }