inboxidle: new class to detect inbox changes

This will be used to implement IMAP IDLE, first.

Eventually, it may be used to trigger other things:

* incremental internal updates for manifest.js.gz
* restart `git cat-file' processes on pack index unlink
* IMAP IDLE-like long-polling HTTP endpoint

And maybe more things we haven't thought of, yet.

It uses Linux::Inotify2 or IO::KQueue depending on what packages
are installed and what the kernel supports.  It falls back to
nanosecond-aware Time::HiRes::stat() (available with Perl 5.10.0+)
on systems lacking Linux::Inotify2 and IO::KQueue.

In the future, a pure Perl alternative to Linux::Inotify2 may be
supplied for users of architectures we already support signalfd
and epoll on.

v2 changes:
- avoid O_TRUNC on lock file
- change ctime on Linux systems w/o inotify
- fix naming of comments and fields

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/PublicInbox/Lock.pm b/lib/PublicInbox/Lock.pm
index 032841ed..693a3794 100644
--- a/lib/PublicInbox/Lock.pm
+++ b/lib/PublicInbox/Lock.pm
@@ -24,6 +24,13 @@ sub lock_release {
         my ($self) = @_;
         return unless $self->{lock_path};
         my $lockfh = delete $self->{lockfh} or croak 'not locked';
+
+        # NetBSD 8.1 and OpenBSD 6.5 (and maybe other versions/*BSDs) lack
+        # NOTE_CLOSE_WRITE from FreeBSD 11+, so trigger NOTE_WRITE, instead.
+        # We also need to change the ctime on Linux systems w/o inotify
+        if ($^O ne 'linux' || !eval { require Linux::Inotify2; 1 }) {
+                syswrite($lockfh, '.');
+        }
         flock($lockfh, LOCK_UN) or die "unlock failed: $!\n";
         close $lockfh or die "close failed: $!\n";
 }