Aha, Interpreter!  I was looking in process for the "swap" method. :)

At the moment, I am not looking to solve a problem per se.  I was just 
thinking that Smalltalk tries to be it's own OS, kind of.  I wonder what 
would happen if it went a bit further.

On a real OS, a processes are only allowed to run for a certain amount of 
time before the CPU interupts them and puts the OS back in control to decide 
what to do next.  In any kind of "green threads" system this (normally) 
isn't doable because it is actually just one running process and if a "green 
thread" doesn't want to yield, then the threading system never gets back in 
control to stop it.  The threading system could, of course, have the OS send 
it some kind of signal ever so many milliseconds but how that is done is 
very platform specific (not to mention a host of other problems with it).

But with an interpreter it would be possible to do the same things an 
advanced OS does, let a process only run for a specific amount of VM 
instructions, penilize processes that keep using their whole "quantum", 
promote processes that don't, etc.

The question is, would this have any benifit? If I ever have time, maybe I 
will find out (unless of course Squeak already does most of this). :)

>From: John M McIntosh <johnmci at smalltalkconsulting.com>
>Reply-To: johnmci at smalltalkconsulting.com,The general-purpose Squeak 
>developers list<squeak-dev at lists.squeakfoundation.org>
>To: The general-purpose Squeak developers 
>list<squeak-dev at lists.squeakfoundation.org>
>Subject: Re: Preemptive scheduling
>Date: Tue, 1 May 2007 11:21:38 -0700
>
>Interpreter>>transferTo: is the place in the VM were we transfer  control 
>from one process to another. This is invoked via
>
>primitiveSuspend
>primitiveWait
>primitiveYield
>resume:
>
>for wait and yield it follows the pattern
>
>		self addLastLink: activeProc toList: processList.
>		self transferTo: self wakeHighestPriority
>
>which means we stick the process at the end of the linked list of  
>processes in the same priority, thus if there was a higher process or
>process at the same priority ready to run it will run instead of the  
>process that has the wait or yield.  It could of course wake the same
>process if the process is the only one in it's priority group and  it's 
>ready to run of course.
>
>for suspend, we don't do the addLastLink because the process is being  
>suspended.
>
>In all of this the ProcessorScheduler does not do preemptive  scheduling, 
>thus if you have a high priority smalltalk process that  runs away it will 
>block all other
>processes from running.  You could of course and I've seen change  sets for 
>Visualworks write your own scheduler that modifies what  
>wakeHighestPriority means by suspending processes that normally would  be 
>runnable.  That would be overhead, and what is the problem you are  trying 
>to solve?
>
>
>On May 1, 2007, at 10:48 AM, J J wrote:
>
>>Hi all,
>>
>>Does the Squeak VM do preemptive scheduling or regular yield style  
>>scheduling.  This may sound like a silly question, but I know  Erlang is 
>>language that does mainly green threads and they are  preemptive in 
>>nature.  They accomplish this by allowing a given  thread to execute no 
>>more then 100 VM instructions before it is  preempted (obviously if a 
>>thread makes a primitive call that is a  voluntary yield).
>>
>>Does Squeak do this already?  I suspect not, and if I am correct,  would 
>>there be any benefit in doing something like this or would it  actually 
>>slow things down?
>>
>>Thanks,
>>Jason
>>
>>_________________________________________________________________
>>Don’t quit your job – Take Classes Online and Earn your Degree in 1  year. 
>>Start Today! http://www.classesusa.com/clickcount.cfm? 
>>id=866146&goto=http%3A%2F%2Fwww.classesusa.com%2Ffeaturedschools% 
>>2Fonlinedegreesmp%2Fform-dyn1.html%3Fsplovr%3D866144
>>
>>
>
>--
>======================================================================== 
>===
>John M. McIntosh <johnmci at smalltalkconsulting.com>
>Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
>======================================================================== 
>===
>
>
>

_________________________________________________________________
Don’t quit your job – Take Classes Online and Earn your Degree in 1 year. 
Start Today! 
http://www.classesusa.com/clickcount.cfm?id=866146&goto=http%3A%2F%2Fwww.classesusa.com%2Ffeaturedschools%2Fonlinedegreesmp%2Fform-dyn1.html%3Fsplovr%3D866144