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, 17 insertions, 0 deletions

diff --git a/lib/PublicInbox/In2Tie.pm b/lib/PublicInbox/In2Tie.pm
new file mode 100644
index 00000000..db1dc104
--- /dev/null
+++ b/lib/PublicInbox/In2Tie.pm
@@ -0,0 +1,17 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# used to ensure PublicInbox::DS can call fileno() as a function
+# on Linux::Inotify2 objects
+package PublicInbox::In2Tie;
+use strict;
+
+sub TIEHANDLE {
+        my ($class, $in2) = @_;
+        bless \$in2, $class; # a scalar reference to an existing reference
+}
+
+# this calls Linux::Inotify2::fileno
+sub FILENO { ${$_[0]}->fileno }
+
+1;