Ian Jackson writes:
> Firstly, let me say that I'm very new to Haskell, so it may be that
> I'm just going about things in a fundamentally wrong way.
>
> I'm writing an application in Haskell which, if I were to write it in
> C, would be an event-driven select-loop based program. It needs to
> handle timeouts, and know when particular external (network) events
> happen.
>
> I was pleased to see that GHC has a library misc/Select which will
> allow me to call select(2). This will allow me to build the
> event-processing arrangements.
I'd suggest using concurrency instead of Select. GHC's I/O subsystem is
designed such that a thread waiting on I/O doesn't halt the whole system, so
you can have several threads doing I/O simultaneously (eg. as in a
multi-threaded server model, where each client is served by an individual
thread).
You can also implement timeouts using threadDelay and asynchronous
exceptions. I've just modified GHC to allow a thread to have more control
over the delivery of asynchronous exceptions: threads can now "block"
asynchronous exceptions during a critical section; this turned out to be
necessary for programming certain types of inter-thread communication using
exceptions.
Cheers,
Simon
