From d6674af04cb74a4efd513d938bed8bf7ab2838eb Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Wed, 27 Nov 2019 01:33:33 +0000
Subject: httpd|nntpd: avoid missed signal wakeups

Our attempt at using a self-pipe in signal handlers was
ineffective, since pure Perl code execution is deferred
and Perl doesn't use an internal self-pipe/eventfd.  In
retrospect, I actually prefer the simplicity of Perl in
this regard...

We can use sigprocmask() from Perl, so we can introduce
signalfd(2) and EVFILT_SIGNAL support on Linux and *BSD-based
systems, respectively.  These OS primitives allow us to avoid a
race where Perl checks for signals right before epoll_wait() or
kevent() puts the process to sleep.

The (few) systems nowadays without signalfd(2) or IO::KQueue
will now see wakeups every second to avoid missed signals.
---
 lib/PublicInbox/DS.pm | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

(limited to 'lib/PublicInbox/DS.pm')

diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index 7f7cb85d..17c640f4 100644
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -53,6 +53,7 @@ our (
      $LoopTimeout,               # timeout of event loop in milliseconds
      $DoneInit,                  # if we've done the one-time module init yet
      @Timers,                    # timers
+     $in_loop,
      );
 
 Reset();
@@ -249,7 +250,7 @@ sub reap_pids {
 sub enqueue_reap ($) { push @$nextq, \&reap_pids };
 
 sub EpollEventLoop {
-    local $SIG{CHLD} = \&enqueue_reap;
+    local $in_loop = 1;
     while (1) {
         my @events;
         my $i;
@@ -628,8 +629,7 @@ sub shutdn ($) {
 # must be called with eval, PublicInbox::DS may not be loaded (see t/qspawn.t)
 sub dwaitpid ($$$) {
     my ($pid, $cb, $arg) = @_;
-    my $chld = $SIG{CHLD};
-    if (defined($chld) && $chld eq \&enqueue_reap) {
+    if ($in_loop) {
         push @$WaitPids, [ $pid, $cb, $arg ];
 
         # We could've just missed our SIGCHLD, cover it, here:
-- 
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