[PATCH 8/7] provide select(2) backend for PublicInbox::DS

[Eric Wong <e@80x24.org>]

This is safer than relying on an internal API of IO::Poll
and doesn't create extra references to IO globs like the
public one.
---
 Not sure if this is redundant or not, or if perhaps dropping
 DSPoll would be preferable, even...

 MANIFEST                  |  2 ++
 lib/PublicInbox/DS.pm     |  6 +++---
 lib/PublicInbox/Select.pm | 40 +++++++++++++++++++++++++++++++++++++++
 t/select.t                |  4 ++++
 4 files changed, 49 insertions(+), 3 deletions(-)
 create mode 100644 lib/PublicInbox/Select.pm
 create mode 100644 t/select.t

diff --git a/MANIFEST b/MANIFEST
index d7a670b8..63287bad 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -331,6 +331,7 @@ lib/PublicInbox/SearchIdxShard.pm
 lib/PublicInbox/SearchQuery.pm
 lib/PublicInbox/SearchThread.pm
 lib/PublicInbox/SearchView.pm
+lib/PublicInbox/Select.pm
 lib/PublicInbox/SharedKV.pm
 lib/PublicInbox/Sigfd.pm
 lib/PublicInbox/Smsg.pm
@@ -578,6 +579,7 @@ t/run.perl
 t/search-amsg.eml
 t/search-thr-index.t
 t/search.t
+t/select.t
 t/sha.t
 t/shared_kv.t
 t/sigfd.t
diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index b3edc094..d47df491 100644
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -31,7 +31,7 @@ use Scalar::Util qw(blessed);
 use PublicInbox::Syscall qw(%SIGNUM
 	EPOLLIN EPOLLOUT EPOLLONESHOT EPOLLEXCLUSIVE);
 use PublicInbox::Tmpfile;
-use PublicInbox::DSPoll;
+use PublicInbox::Select;
 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);
@@ -43,7 +43,7 @@ my $reap_armed;
 my $ToClose; # sockets to close when event loop is done
 our (
      %DescriptorMap,             # fd (num) -> PublicInbox::DS object
-     $Poller, # global Epoll, DSPoll, or DSKQXS ref
+     $Poller, # global Select, Epoll, DSPoll, or DSKQXS ref
 
      @post_loop_do,              # subref + args to call at the end of each loop
 
@@ -83,7 +83,7 @@ sub Reset {
 
 	$reap_armed = undef;
 	$LoopTimeout = -1;  # no timeout by default
-	$Poller = PublicInbox::DSPoll->new;
+	$Poller = PublicInbox::Select->new;
 }
 
 =head2 C<< CLASS->SetLoopTimeout( $timeout ) >>
diff --git a/lib/PublicInbox/Select.pm b/lib/PublicInbox/Select.pm
new file mode 100644
index 00000000..9df3a6bd
--- /dev/null
+++ b/lib/PublicInbox/Select.pm
@@ -0,0 +1,40 @@
+# Copyright (C) all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+#
+# This makes select(2) look like epoll to simplify the code in DS.pm.
+# Unlike IO::Select, it does NOT hold references to IO handles.
+# This is NOT meant to be an all encompassing emulation of epoll
+# via select, but only to support cases we care about.
+package PublicInbox::Select;
+use v5.12;
+use PublicInbox::Syscall qw(EPOLLONESHOT EPOLLIN EPOLLOUT);
+
+sub new { bless {}, __PACKAGE__ } # fd => events
+
+sub ep_wait {
+	my ($self, $maxevents, $msec, $events) = @_;
+	my ($rvec, $wvec) = ('', ''); # we don't use EPOLLERR
+	while (my ($fd, $ev) = each %$self) {
+		vec($rvec, $fd, 1) = 1 if $ev & EPOLLIN;
+		vec($wvec, $fd, 1) = 1 if $ev & EPOLLOUT;
+	}
+	@$events = ();
+	my $n = select($rvec, $wvec, undef, $msec < 0 ? undef : ($msec/1000));
+	return if $n <= 0;
+	while (my ($fd, $ev) = each %$self) {
+		if (vec($rvec, $fd, 1) || vec($wvec, $fd, 1)) {
+			delete($self->{$fd}) if $ev & EPOLLONESHOT;
+			push @$events, $fd;
+		}
+	}
+	$n == scalar(@$events) or
+		warn "BUG? select() returned $n, but got ".scalar(@$events);
+}
+
+sub ep_del { delete($_[0]->{fileno($_[1])}); 0 }
+sub ep_add { $_[0]->{fileno($_[1])} = $_[2]; 0 }
+
+no warnings 'once';
+*ep_mod = \&ep_add;
+
+1;
diff --git a/t/select.t b/t/select.t
new file mode 100644
index 00000000..e8032c5a
--- /dev/null
+++ b/t/select.t
@@ -0,0 +1,4 @@
+# Copyright (C) all contributors <meta@public-inbox.org>
+use v5.12;
+local $ENV{TEST_IOPOLLER} = 'PublicInbox::Select';
+require './t/ds-poll.t';