Concurrency (was: RE: Re[2]: important news: refocusingdiscussion)

Simon Marlow simonmar at
Wed Mar 29 05:56:41 EST 2006

On 29 March 2006 10:16, John Meacham wrote:

> On Mon, Mar 27, 2006 at 03:36:55PM +0100, Simon Marlow wrote:
>>  (b) it is unlikely that Hugs or JHC will implement concurrency
>>      even if it goes into the standard
> Well, if the standard is unimplemented for certain compilers,  I think
> we need to work on the standard because that would be a deficiency of
> it. I would very much like to be able to write portable concurrent
> programs which doesn't necessarily mean GHC style concurrency or
> nothing. 
> given the choice between
> 1. a standard specifying something most people can't implement
> 2. a widely available but not mentioned in the standard extension
> 2 seems much more preferable and we should err on that side.

Fair enough - I take that as a vote for a concurrency addendum.

I think it's a bit unfair to talk about "GHC-style concurrency".  There
are many different ways to implement exactly what GHC currently
provides.  In fact, we were very careful when designing it to ensure
that this was the case:

 1. one OS thread per Haskell thread, giant lock around the runtime

 2. one OS thread for the runtime, fork OS threads for foreign

 3. hybrid implementation with a pool of OS threads (GHC's

You even mention another implementation that we hadn't considered:

 4. one OS thread per Haskell thread but no lock around the runtime,
    with possibly repeated work.

YHC uses (2), for reference.  You're proposing (4) as one possibility
for JHC.


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