From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-09-21T10:18:37+09:00
Subject: Re: signals handlers and threads

On Wed, 21 Sep 2005, Rick Nooner wrote:


> I smell deadlock issues.  I have always delegated any shared resource action
> required by a signal handler to another thread.

great - this is actually what i am doing:

   trap 'INT' { handle_requests }

   ...

   loop{ sleep }

   ...

   def handle_requests
     Thread::new{ ... }
   end

so perhaps i'm o.k.  the code is running on linux and cygwin now - but i'm
having issues with Process::kill returning EINVAL on windows...  googling...


> The problem is that a signal is an async event that can interrupt your
> process in an indeterminate state.  You should do as little as possible in
> the signal handler and delegate any real work to something in the main flow
> of the program, say another thread.

right-o.  that's the approach i'm taking alright.

> One way is to set up a queue where the reader is the other thread that
> actually does whatever is required by the signal handler with the shared
> resource.

in my case the handler scan a directory for new requests - so it's not even
important if any signals are missed while handling another.  so long as the
scanning takes place.

basically i'm working on a new model for acgi whereby

   - c program intercepts request, marshals env and stdin to file
   - signals ruby server, which basically loops handling requests
   - c program waits for signal from ruby server
   - c program relays stdout and stderr written from ruby server

sounds like too much work - but if you consider it for while it provides the
highests throughput for the server since a separate thread can be spawned for
each request - something you can't do when you need to write to STDOUT, etc.
i haven't gotten it work yet - but i'm worried the signal handling won't map
well to windows...

thanks for the reply.

cheers.

-a
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