From: Matt Harrison <iwasinnamuknow@...>
Date: 2011-06-16T09:54:40+09:00
Subject: Re: queues? inotify? anything else?

On 16/06/2011 00:10, Eric Wong wrote:
> Matt Harrison<iwasinnamuknow@genestate.com>  wrote:
>> I would like to be able to add file while the script is busy and
>> have it append the new filename to its list. I've considered inotify
>> type monitoring but I don't know much about it and if it could be
>> made to fit this single-threaded script.
>
> Inotify descriptors have an internal queue[1] so events can be
> backlogged while your script is doing something else.
>
> The sleepy_penguin[2] RubyGem provides inotify bindings that are
> subclasses of Ruby IO objects, so you can IO.select on them in
> an event loop (sleepy_penguin also provides an epoll wrapper).
>
> sleepy_penguin is Linux-only and a fairly "raw" interface to the
> underlying system calls.  Cool.io (libev wrapper)[3] and EventMachine[4]
> also support inotify and they may be more portable to systems without
> inotify (using kqueue or stat() loops).
>
>> I've also thought about re-reading the directory after each file
>> operation is complete, and adding the previously unknown filenames
>> to the list.
>
> I had to do this once in a daemon since it ran on an NFS directory
> since inotify doesn't work on NFS :<
>
>
> [1] The inotify(7) manpage is a great resource for learning about
>      how it works.
> [2] http://bogomips.org/sleepy_penguin (disclaimer: I'm the author)
> [3] http://coolio.github.com/
> [4] http://rubyeventmachine.com/

Thanks Eric,

I'll read up on inotify when I get some time. I'm not quite 
understanding how it would work with a single-threaded process. I mean, 
if it's busy processing data, I don't see how it could receive events.

I'm sure it'll become more clear as I read up.

Thanks