[Haskell] select(2) or poll(2)-like function?

[Piyush P Kurur]

On Mon, Apr 18, 2011 at 07:55:57AM -0400, Mike Meyer wrote:
> On Mon, 18 Apr 2011 12:56:39 +0200
> Ertugrul Soeylemez <es at ertes.de> wrote:
> > 
> > You also don't need Emacs/Vim, if all you want is to write a simple
> > plain text file.  There is nothing wrong with concurrency, because you
> > are confusing the high level model with the low level implementation.
> > Concurrency is nothing but a design pattern, and GHC shows that a high
> > level design pattern can be mapped to efficient low level code.
> 
> Possibly true. The question is - can it be mapped to a design that's
> as robust and scalable as the ones I'm used to working on?

  I have not written any such server so take my response with a pinch
of salt but I believe that the forkIO based solution does indeed scale
to 10K clients. Internally the runtime uses epoll or kqueue to
simulate the concurrency, so I don't see why it should be slower. May
be you can check with the developers of Network.Wai or the Happstack
server developers. They might be in a better possition to explain.

> [snip]
> > Perhaps Haskell is the wrong language for you.  How about programming in
> > C/C++?  I think you want more control over low level resources than
> > Haskell gives you.  But I suggest having a closer look at concurrency.
> 
> Personally, I don't want to have to worry about low-level resources,
> or even concurrency. Having to do so feels to much like having to
> explicitly allocate and free memory, or worry about register
> allocations. But if I have to do those things to get robustness and
> scalability until the languages start being able to deal with it, then
> I need the RTS to get out of the way and let me do my job.

  I think it would be good idea to prototype what you want to do and
have a try. Most likely I would think you would be surprised with the
efficiency.

> If I'm using a value that needs protection from concurrent access
> without providing that protection, I want the system give me an
> error. At run-time is acceptable, but compile time is better.


Try STM's. They are great abstractions for shared states.

Regards

ppk