[lug] Fwd: Simple counter?

[Bear Giles]

It's the concurrency that will get you. Even locks might not work if the
underlying filesystem doesn't properly support them. That's why I was
thinking along the lines of a named pipe - that way you have a single
process on the other end of the pipe.

The database sequence is another possibility. I wouldn't use mysql though -
there are lightweight JVM databases (e.g., H2) and you could also
investigate SQLite.

Re-reading the same value will always be problematic outside of a database
transaction though - how do you know some other process asn't gotten a
newer value in the interrim? The only way to be really sure is to cache the
information in your own process somehow and again that's adding a lot of
weight to the code.


On Fri, May 24, 2013 at 7:09 PM, Anthony Foiani <tkil at scrye.com> wrote:

>
> Derp, I missed these points.
>
> My solution uses a plain text file; a bit slower to parse/write than
> binary, but easier to use from the command line.  In particualr:
>
> "Jeffrey S. Haemer" <jeffrey.haemer at gmail.com> writes:
>
> > It would be nice if I could give it a seed -- "start with 12" or
> > something -- but that's not critical.
>
> Write the value to the file before you start using it.  Or anytime
> after using it.
>
> (But note that I'm only using advisory locks, so if you muck with it
> while an instance of 'counter' is trying to use the file, you might
> corrupt things.)
>
> > It would be nice if I could ask it what the next number will be
> > without bumping the counter.  Also not critical.
>
> It's a text file; just 'cat' it.
>
> > It would even be nice if it offered remote access, so all machines
> > could use the same counter.  Again, not critical.
>
> ssh 'cat ...'
>
> Although I could see 'counterd', which is a server... ;->
>
> > Honest: this isn't "How can I write a simple program to do this?"
> > It's, "Hasn't someone created a simple, standard utility that does
> > this in the past 20 or 30 years?"
>
> It's simple enough that I could write mine in less than an hour (and
> it would have been 5min if I weren't being picky about return values).
>
> It's complex enough (look at your requests above -- starting value,
> current value, next value, remote access) that there's probably not a
> single easy way to satisfy everyone.  E.g., if you were to make it
> network transparent, then you'd get complaints from the people who
> only want to use it locally.
>
> t.
>
>
> _______________________________________________
> Web Page:  http://lug.boulder.co.us
> Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug
> Join us on IRC: irc.hackingsociety.org port=6667 channel=#hackingsociety
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lug.boulder.co.us/pipermail/lug/attachments/20130524/793f3885/attachment.html>