thread priorities?

[Malcolm Wallace]

> > Thinking about it some. I think we will need some sort of very basic
> > thread priorities.
>
> I'd rather not, if we can avoid it.

Agreed.  If someone wants to provide them as an optional extra, fine.
(We had thread priorities In concurrent embedded Gofer, a long time ago.
They can certainly be useful when interfacing with hardware, but there
are other ways to achieve the same goals.)

As Simon says:

> Priorities come with a whole can of worms that I'd rather not deal with.

They certainly do.  Unintentional priority inversion is the most basic
problem, covered early in any course on real-time systems.

> threadSetPriority :: ThreadID -> Int -> IO ()

In any case, if priorities were to be introduced, I would not use Ints
to represent them.  How many priority levels are sufficient?  A partial
ordering between ThreadIDs would be preferable.  Sometimes priorities are
genuinely incomparable, so there is no point in forcing a particular
ordering.

Regards,
    Malcolm