[Haskell-cafe] Re: concurrent haskell: thread priorities

[Neal Alexander]

Bulat Ziganshin wrote:
> Hello Neal,
> 
> Monday, December 22, 2008, 11:07:32 PM, you wrote:
> 
>> The threaded RT creates an OS thread for each CPU/core on the system and
>> uses them to multiplex userland threads. These are context switched 
>> whenever they block/yield/gc and no priorities can be assigned.
> 
> not exactly. amount of OS threads created controlled by +RTS -N option
> to the program; unless program has special function that RTS calls to
> set up this value
> 
> they are switched on every minor GC which by default occurs after
> each 256kb allocated which is rather frequent event
> 
>> It seems like we could get some priority based scheduling (and still be
>> slackers) if we allow marked green threads to be strictly associated 
>> with a specific OS thread (forkChildIO?).
> 
> forkOS creates new haskell thread and new OS thread specially for it
> 

The docs say that the forkOS thread is still scheduled by the Haskell RT 
though. What would happen if you bump its priority through FFI?

What about this scenario:

forkOS = OS thread A1, Haskell Thread A2
forkIO = Haskell thread B

Could thread B potentially be run on thread A1? Would the RT yield 
thread A2 to give time to another Haskell thread?