[PATCH 1/9] ds: improve DS->Reset fork-safety

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

None of these fixes affect current public-inbox-* code, or even
normal uses of lei.  However, lei users wanting to switch
between $HOME directories or use alternate store paths may
notice strange behavior and this fixes some of it.

We'll also loop to account for DESTROY callbacks inserting into
container objects and retry appropriately.
---
 lib/PublicInbox/DS.pm | 76 ++++++++++++++++++++++++++-----------------
 1 file changed, 46 insertions(+), 30 deletions(-)

diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index 15ece4df..c881c895 100644
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -35,9 +35,10 @@ use Errno qw(EAGAIN EINVAL);
 use Carp qw(carp croak);
 our @EXPORT_OK = qw(now msg_more dwaitpid add_timer);
 
+our %Stack;
 my $nextq; # queue for next_tick
 my $wait_pids; # list of [ pid, callback, callback_arg ]
-my $later_queue; # list of callbacks to run at some later interval
+my $later_q; # list of callbacks to run at some later interval
 my $EXPMAP; # fd -> idle_time
 our $EXPTIME = 180; # 3 minutes
 my ($later_timer, $reap_armed, $exp_timer);
@@ -65,19 +66,27 @@ Reset();
 Reset all state
 
 =cut
+our %state;
 sub Reset {
-    $in_loop = undef; # first in case DESTROY callbacks use this
-    %DescriptorMap = ();
-    $wait_pids = $later_queue = $reap_armed = undef;
-    $EXPMAP = {};
-    $nextq = $ToClose = $later_timer = $exp_timer = undef;
-    $LoopTimeout = -1;  # no timeout by default
-    @Timers = ();
-
-    $PostLoopCallback = undef;
-
-    $_io = undef; # closes real $Epoll FD
-    $Epoll = undef; # may call DSKQXS::DESTROY
+	do {
+		$in_loop = undef; # first in case DESTROY callbacks use this
+		%DescriptorMap = ();
+		@Timers = ();
+		$PostLoopCallback = undef;
+
+		# we may be iterating inside one of these on our stack
+		my @q = delete @Stack{keys %Stack};
+		for my $q (@q) { @$q = () }
+		$EXPMAP = {};
+		$wait_pids = $later_q = $nextq = $ToClose = undef;
+		$_io = undef; # closes real $Epoll FD
+		$Epoll = undef; # may call DSKQXS::DESTROY
+	} while (@Timers || keys(%Stack) || $nextq || $wait_pids ||
+		$later_q || $ToClose || keys(%DescriptorMap) ||
+		$PostLoopCallback);
+
+	$reap_armed = $later_timer = $exp_timer = undef;
+	$LoopTimeout = -1;  # no timeout by default
 }
 
 =head2 C<< CLASS->SetLoopTimeout( $timeout ) >>
@@ -160,17 +169,19 @@ C<PostLoopCallback> below for how to exit the loop.
 sub now () { clock_gettime(CLOCK_MONOTONIC) }
 
 sub next_tick () {
-    my $q = $nextq or return;
-    $nextq = undef;
-    for my $obj (@$q) {
-        # we avoid "ref" on blessed refs to workaround a Perl 5.16.3 leak:
-        # https://rt.perl.org/Public/Bug/Display.html?id=114340
-        if (blessed($obj)) {
-            $obj->event_step;
-        } else {
-            $obj->();
-        }
-    }
+	my $q = $nextq or return;
+	$nextq = undef;
+	$Stack{cur_runq} = $q;
+	for my $obj (@$q) {
+		# avoid "ref" on blessed refs to workaround a Perl 5.16.3 leak:
+		# https://rt.perl.org/Public/Bug/Display.html?id=114340
+		if (blessed($obj)) {
+			$obj->event_step;
+		} else {
+			$obj->();
+		}
+	}
+	delete $Stack{cur_runq};
 }
 
 # runs timers and returns milliseconds for next one, or next event loop
@@ -221,6 +232,7 @@ sub reap_pids {
 	$reap_armed = undef;
 	my $tmp = $wait_pids or return;
 	$wait_pids = undef;
+	$Stack{reap_runq} = $tmp;
 	my $oldset = block_signals();
 	foreach my $ary (@$tmp) {
 		my ($pid, $cb, $arg) = @$ary;
@@ -237,6 +249,7 @@ sub reap_pids {
 		}
 	}
 	sig_setmask($oldset);
+	delete $Stack{reap_runq};
 }
 
 # reentrant SIGCHLD handler (since reap_pids is not reentrant)
@@ -271,7 +284,6 @@ sub EventLoop {
     $Epoll //= _InitPoller();
     local $in_loop = 1;
     my @events;
-    my $obj; # guard stack-not-refcounted w/ Carp + @DB::args
     do {
         my $timeout = RunTimers();
 
@@ -282,7 +294,9 @@ sub EventLoop {
             # that ones in the front triggered unregister-interest actions.  if we
             # can't find the %sock entry, it's because we're no longer interested
             # in that event.
-            $obj = $DescriptorMap{$fd};
+
+	    # guard stack-not-refcounted w/ Carp + @DB::args
+            my $obj = $DescriptorMap{$fd};
             $obj->event_step;
         }
     } while (PostEventLoop());
@@ -646,13 +660,15 @@ sub dwaitpid ($;$$) {
 }
 
 sub _run_later () {
-	my $run = $later_queue or return;
-	$later_timer = $later_queue = undef;
-	$_->() for @$run;
+	my $q = $later_q or return;
+	$later_timer = $later_q = undef;
+	$Stack{later_q} = $q;
+	$_->() for @$q;
+	delete $Stack{later_q};
 }
 
 sub later ($) {
-	push @$later_queue, $_[0]; # autovivifies @$later_queue
+	push @$later_q, $_[0]; # autovivifies @$later_q
 	$later_timer //= add_timer(60, \&_run_later);
 }