[PATCH 36/36] on_destroy: support PID owner guard

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

Since we'll be forking for Xapian indexing and maybe
other places, having a simple guard in place to ensure
OnDestroy doesn't unexpectedly unlink files or similar
is a safer option.
---
 lib/PublicInbox/LEI.pm       | 5 ++---
 lib/PublicInbox/Lock.pm      | 4 ++--
 lib/PublicInbox/OnDestroy.pm | 5 +++++
 script/public-inbox-init     | 2 +-
 t/on_destroy.t               | 9 +++++++++
 5 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index b84e24ef..4af85d49 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -745,9 +745,8 @@ sub lazy_start {
 	# reading the <$daemon> pipe.
 	openlog($path, 'pid', 'user');
 	local $SIG{__WARN__} = sub { syslog('warning', "@_") };
-	my $owner_pid = $$;
-	my $on_destroy = PublicInbox::OnDestroy->new(sub {
-		syslog('crit', "$@") if $@ && $$ == $owner_pid;
+	my $on_destroy = PublicInbox::OnDestroy->new($$, sub {
+		syslog('crit', "$@") if $@;
 	});
 	open STDERR, '>&STDIN' or die "redirect stderr failed: $!";
 	open STDOUT, '>&STDIN' or die "redirect stdout failed: $!";
diff --git a/lib/PublicInbox/Lock.pm b/lib/PublicInbox/Lock.pm
index f6eaa5ce..1d0b4f9c 100644
--- a/lib/PublicInbox/Lock.pm
+++ b/lib/PublicInbox/Lock.pm
@@ -36,9 +36,9 @@ sub lock_release {
 
 # caller must use return value
 sub lock_for_scope {
-	my ($self) = @_;
+	my ($self, @single_pid) = @_;
 	$self->lock_acquire;
-	PublicInbox::OnDestroy->new(\&lock_release, $self);
+	PublicInbox::OnDestroy->new(@single_pid, \&lock_release, $self);
 }
 
 sub new_tmp {
diff --git a/lib/PublicInbox/OnDestroy.pm b/lib/PublicInbox/OnDestroy.pm
index 841f87d4..65ebd7dc 100644
--- a/lib/PublicInbox/OnDestroy.pm
+++ b/lib/PublicInbox/OnDestroy.pm
@@ -10,6 +10,11 @@ sub new {
 
 sub DESTROY {
 	my ($cb, @args) = @{$_[0]};
+	if (!ref($cb)) {
+		my $pid = $cb;
+		return if $pid != $$;
+		$cb = shift @args;
+	}
 	$cb->(@args) if $cb;
 }
 
diff --git a/script/public-inbox-init b/script/public-inbox-init
index 693f5ca1..222d0c60 100755
--- a/script/public-inbox-init
+++ b/script/public-inbox-init
@@ -92,7 +92,7 @@ sysopen($lockfh, $lockfile, O_RDWR|O_CREAT|O_EXCL) or do {
 	exit(255);
 };
 require PublicInbox::OnDestroy;
-my $auto_unlink = PublicInbox::OnDestroy->new(sub { unlink $lockfile });
+my $auto_unlink = PublicInbox::OnDestroy->new($$, sub { unlink $lockfile });
 my ($perm, %seen);
 if (-e $pi_config) {
 	open(my $oh, '<', $pi_config) or die "unable to read $pi_config: $!\n";
diff --git a/t/on_destroy.t b/t/on_destroy.t
index 8b85b48e..0de67d0b 100644
--- a/t/on_destroy.t
+++ b/t/on_destroy.t
@@ -16,6 +16,15 @@ $od = PublicInbox::OnDestroy->new(sub { @x = @_ }, qw(x y));
 undef $od;
 is_deeply(\@x, [ 'x', 'y' ], '2 args passed');
 
+open my $tmp, '+>>', undef or BAIL_OUT $!;
+$tmp->autoflush(1);
+$od = PublicInbox::OnDestroy->new(1, sub { print $tmp "$$ DESTROY\n" });
+undef $od;
+is(-s $tmp, 0, '$tmp is empty on pid mismatch');
+$od = PublicInbox::OnDestroy->new($$, sub { $tmp = $$ });
+undef $od;
+is($tmp, $$, '$tmp set to $$ by callback');
+
 if (my $nr = $ENV{TEST_LEAK_NR}) {
 	for (0..$nr) {
 		$od = PublicInbox::OnDestroy->new(sub { @x = @_ }, qw(x y));