RE: preemptive vs cooperative: attempt at formalization

On 12 April 2006 11:41, Malcolm Wallace wrote:

John Meacham wrote:

...

In a concurrent implementation, a thread performing an infinite loop with no IO or interaction with the outside world can potentially stall switching to another thread forever, in FP, we usually denote an infinite loop by _|_. so I think the first difference would be:

By infinite loop, you mean both non-terminating, and non-productive. A non-terminating but productive pure computation (e.g. ones = 1:ones) is not necessarily a problem.

That's slightly odd terminology. ones = 1:ones is definitely terminating. (length ones) is not, though.

Why? Because ultimately the demand that forces production of the infinite data structure must come from somewhere, and that somewhere must essentially be I/O. (The only alternative consumers are terminating pure (no problem), non-terminating productive pure (so look upward to its demand), or an unproductive non-terminating computation, which brings us full circle.)

It is a curious artifact that in certain multi-threaded implementations, a non-terminating non-productive thread does not make the entire system unproductive,

Wow. I wish I knew what that meant :) Maybe you could expand on in what sense you mean non-terminating, and what "productive" means? Is there something we need to worry about here? Cheers, Simon