From 34c1a6c16733adee3acfe5861096692f3ea55378 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@yhbt.net>
Date: Wed, 10 Jun 2020 07:04:01 +0000
Subject: 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
---
 lib/PublicInbox/FakeInotify.pm | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 lib/PublicInbox/FakeInotify.pm

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

diff --git a/lib/PublicInbox/FakeInotify.pm b/lib/PublicInbox/FakeInotify.pm
new file mode 100644
index 00000000..bd610463
--- /dev/null
+++ b/lib/PublicInbox/FakeInotify.pm
@@ -0,0 +1,39 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# for systems lacking Linux::Inotify2 or IO::KQueue, just emulates
+# enough of Linux::Inotify2
+package PublicInbox::FakeInotify;
+use strict;
+use Time::HiRes qw(stat);
+my $IN_CLOSE = 0x08 | 0x10; # match Linux inotify
+
+sub new { bless { watch => {} }, __PACKAGE__ }
+
+# behaves like Linux::Inotify2->watch
+sub watch {
+	my ($self, $path, $mask, $cb) = @_;
+	my @st = stat($path) or return;
+	$self->{watch}->{"$path\0$mask"} = [ @st, $cb ];
+}
+
+# behaves like non-blocking Linux::Inotify2->poll
+sub poll {
+	my ($self) = @_;
+	my $watch = $self->{watch} or return;
+	for my $x (keys %$watch) {
+		my ($path, $mask) = split(/\0/, $x, 2);
+		my @now = stat($path) or next;
+		my $prv = $watch->{$x};
+		my $cb = $prv->[-1];
+		# 10: ctime, 7: size
+		if ($prv->[10] != $now[10]) {
+			if (($mask & $IN_CLOSE) == $IN_CLOSE) {
+				eval { $cb->() };
+			}
+		}
+		@$prv = (@now, $cb);
+	}
+}
+
+1;
-- 
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