Re: Are Perl6 threads preemptive or cooperative?

> Writing a threads package correctly is a non-trivial thing to do. 

We don't have to write a threads package.
We just have to thread the interpreter.
There's a difference.

> Perl doesn't currently run on a system that doesn't have a reasonably good 
> threading library. 

I abandoned an NT -> Mac port because Mac OS thread support is so
weak. And, as it happens, Mac OS only provides cooperative threads.

If Mac OS X ships before Perl6, I will concede the point.


I'm not arguing that cooperative threads are particularly desirable,
or that writing our own cooperative threading system is trivial or
specially easy. 

Rather, I am pointing out that we have, in principle, two
alternatives

Plan A
Make the Perl interpreter thread-safe and run it on the preemptive
thread package provided by each platform.

Plan B
Implement cooperative threads inside the interpreter, and handle
synchronization issues by only yield()ing when it is safe to do so.

AND

I am suggesting that B may be easier to do than A. Here's an example
of why this could be the case:

	Thread1		Thread2
	$a = $b;	$b = $a;

preemptive threading requires
- mutexes to protect $a and $b
- a robust deadlock avoidance strategy

cooperative threading requires
- don't yield inside a statement


I'd rather have preemptive threads than cooperative threads, but we
should understand
- what we are getting ourselves into
- what the alternatives are


- SWM