Proposal: add forkOnIO and friends to Control.Concurrent:

[Duncan Coutts]

On 22 December 2010 11:41, Simon Marlow <marlowsd at gmail.com> wrote:
> Ticket:
>
>  http://hackage.haskell.org/trac/ghc/ticket/4859
>
> I think these functions are implementation-independent enough to add to the
> main `Control.Concurrent` API:
>
> {{{
> {- |
> Like 'forkIO', but lets you specify on which CPU the thread is
> created.  Unlike a `forkIO` thread, a thread created by `forkOnIO`
> will stay on the same CPU for its entire lifetime (`forkIO` threads
> can migrate between CPUs according to the scheduling policy).
> `forkOnIO` is useful for overriding the scheduling policy when you
> know in advance how best to distribute the threads.
>
> The `Int` argument specifies the CPU number; it is interpreted modulo
> the value returned by 'getNumCapabilities'.

While Int is clearly enough for a multi-processors single node system,
I wonder if there is something slightly more general that would give
us a common API with the Eden / distributed Haskell people. For
example in MPI the identification of a node is rather more complex
than a single integer. Perhaps some more abstract identifier for a
capability would be useful. Closely related of course is how one
discovers the available capabilities.

Duncan