sinotify

by Steven Swerling

rdoc | github

DESCRIPTION:

ALPHA Alert – just uploaded initial release.

Linux inotify is a means to receive events describing file system activity (create, modify, delete, close, etc).

Sinotify was derived from aredridel’s package (raa.ruby-lang.org/project/ruby-inotify/), with the addition of Paul Boon’s tweak for making the event_check thread more polite (see www.mindbucket.com/2009/02/24/ruby-daemons-verifying-good-behavior/)

In sinotify, the classes Sinotify::PrimNotifier and Sinotify::PrimEvent provide a low level wrapper to inotify, with the ability to establish ‘watches’ and then listen for inotify events using one of inotify’s synchronous event loops, and providing access to the events’ masks (see ‘man inotify’ for details). Sinotify::PrimEvent class adds a little semantic sugar to the event in to the form of ‘etypes’, which are just ruby symbols that describe the event mask. If the event has a raw mask of (DELETE_SELF & IS_DIR), then the etypes array would be [:delete_self, :is_dir].

In addition to the ‘straight’ wrapper in inotify, sinotify provides an asynchronous implementation of the ‘observer pattern’ for notification. In other words, Sinotify::Notifier listens in the background for inotify events, adapting them into instances of Sinotify::Event as they come in and immediately placing them in a concurrent queue, from which they are ‘announced’ to ‘subscribers’ of the event. [Sinotify uses the ‘cosell’ implementation of the Announcements event notification framework, hence the terminology ‘subscribe’ and ‘announce’ rather then ‘listen’ and ‘trigger’ used in the standard event observer pattern. See the ‘cosell’ package on github for details.]

A variety of ‘knobs’ are provided for controlling the behavior of the notifier: whether a watch should apply to a single directory or should recurse into subdirectores, how fast it should broadcast queued events, etc (see Sinotify::Notifier, and the example in the synopsis section below). An event ‘spy’ can also be setup to log all Sinotify::PrimEvents and Sinotify::Events.

Sinotify::Event simplifies inotify’s muddled event model, sending events only for those files/directories that have changed. That’s not to say you can’t setup a notifier that recurses into subdirectories, just that any individual event will apply to a single file, and not to its children. Also, event types are identified using words (in the form of ruby :symbols) instead of inotify’s event masks. See Sinotify::Event for more explanation.

The README for inotify:

http://www.kernel.org/pub/linux/kernel/people/rml/inotify/README

Selected quotes from the README for inotify:

* "Rumor is that the 'd' in 'dnotify' does not stand for 'directory' but for 'suck.'"

* "The 'i' in inotify does not stand for 'suck' but for 'inode' -- the logical
  choice since inotify is inode-based."

(The ‘s’ in ‘sinotify’ does in fact stand for ‘suck.’)

FEATURES/PROBLEMS:

  • None known. But it’s still early.

SYNOPSIS:

Try this:

$ mkdir /tmp/sinotify_test
$ irb
require 'sinotify'
notifier = Sinotify::Notifier.new('/tmp/sinotify_test', :recurse => true, :etypes => [:create, :modify, :delete])
notifier.spy!(:logger => Logger.new('/tmp/inotify_spy.log')) # optional event spy
notifier.when_announcing(Sinotify::Event) do |sinotify_event|
  puts "Event happened at #{sinotify_event.timestamp} on #{sinotify_event.path}, etypes => #{sinotify_event.etypes.inspect}"
end
notifier.when_announcing(Sinotify::Event) do |sinotify_event|
  puts "    --> demonstrate that multiple subscribers can be setup: #{sinotify_event.etypes.inspect}"
end
notifier.watch! # don't forget to start the watch

Then in another linux console: 

$ touch /tmp/sinotify_test/hi && sleep 1 && echo 'hello' >> /tmp/sinotify_test/hi && sleep 1 && rm -r /tmp/sinotify_test

Back in irb you will see:

Event happened at Sat Jul 11 12:29:18 -0400 2009 on /tmp/sinotify_test/hi, etypes => [:create]
    --> demonstrate that multiple subscribers can be setup: [:create]
Event happened at Sat Jul 11 12:29:19 -0400 2009 on /tmp/sinotify_test/hi, etypes => [:modify]
    --> demonstrate that multiple subscribers can be setup: [:modify]
Event happened at Sat Jul 11 12:29:20 -0400 2009 on /tmp/sinotify_test/hi, etypes => [:delete]
    --> demonstrate that multiple subscribers can be setup: [:delete]
Event happened at Sat Jul 11 12:29:20 -0400 2009 on /tmp/sinotify_test, etypes => [:delete]
    --> demonstrate that multiple subscribers can be setup: [:delete]

tail -n 50 -f /tmp/inotify_spy.log:

...
... INFO -- : Sinotify::Notifier Prim Event Spy: <Sinotify::PrimEvent :name => 'hi', :etypes => [:create], :mask => 100 ...
... INFO -- : Sinotify::Notifier Event Spy <Sinotify::Event :path => '/tmp/sinotify_test/hi', dir? => false, :etypes =>  ...
... INFO -- : Sinotify::Notifier Prim Event Spy: <Sinotify::PrimEvent :name => 'hi', :etypes => [:modify], :mask => 2 ...
... INFO -- : Sinotify::Notifier Event Spy <Sinotify::Event :path => '/tmp/sinotify_test/hi', dir? => false, :etypes => ...
... INFO -- : Sinotify::Notifier Prim Event Spy: <Sinotify::PrimEvent :name => 'hi', :etypes => [:delete], :mask => 200 ...
... INFO -- : Sinotify::Notifier Event Spy <Sinotify::Event :path => '/tmp/sinotify_test/hi', dir? => false, :etypes => ...
... INFO -- : Sinotify::Notifier Prim Event Spy: <Sinotify::PrimEvent :name => '', :etypes => [:delete_self], :mask => 400 ...
... INFO -- : Sinotify::Notifier Event Spy <Sinotify::Event :path => '/tmp/sinotify_test', dir? => true, :etypes => [:delete]...
etc.

REQUIREMENTS:

  • linux inotify dev libs

  • cosell announcements framework gem

INSTALL:

  • Todo: install instruction

  • sudo gem install cosell…

  • sudo gem install sinotify…

LICENSE:

(The MIT License)

Copyright © 2008 FIXME (different license?)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.