[Catalyst] timeouts

[Yuval Kogman]

On Thu, Apr 13, 2006 at 16:49:41 -0500, Peter Karman wrote:
> greetings cattle-lusters,
> 
> I've got a Cat app where I'm running into issues with DBI timeouts. I'm 
> using raw DBI, but as I know there are lots of ORM developers here as 
> well as us mere mortal Cat-rustlers, wondering how folks deal with this 
> situation:
> 
>   sub foo : Local
>   {

		eval {
			local $SIG{ALRM} = sub { die };
			alarm $timeout;

>     # create dbi object, prepare, execute
>     # but at least one of those steps results in a long
>     # delay due to ... whatever (traffic, load, etc.)

			alarm 0; # cancel the timeout

			$value; # return it
		}
>   }


Perhaps you should really make it into something like do_txn, that
takes a sub and executes it in this timed out eval, so that you
have:

	my $value = $self->with_timeout( 10, sub {
		....
	});

> The DBI pod refers to Sys::SigAction as a good timeout handler. I'm 
> headed that way. But wonder how folks deal with timeouts in Cat apps 
> when a controller sends off for some info and there's a wait coming 
> back. A quick cpan search for 'catalyst plugin alarm' didn't turn up 
> anything.

I'm guessing Sys::SigAction is pretty compatible with what I just
proposed.

Either way, Catalyst does not (currently) make use of 'alarm'
anywhere. The problem with alarms is that they're process global. I
don't knoww how this behaves in mod_perl, but you should find out on
e.g. the mod_perl mailinglist/channel/manual.

I have a suspicion that you can use Time::HirRes's itimers to get
around this one per process limitation.

> I've got another example doing login auth against a server that may or 
> may not feel like responding immediately. Since I'm using LWP::UserAgent 
> in that case I just set the timeout explicitly, but DBI is a little 
> trickier.

I am almost sure LWP::UserAgent does exactly what I pasted above -
it's very standard (I know for a fact that Net::Ping does it, since
that's where I learned it ;-)

-- 
  Yuval Kogman <nothingmuch at woobling.org>
http://nothingmuch.woobling.org  0xEBD27418

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