RE: JavaMemoryModel: Fairness Guarantees in the Memory Model?

From: Doug Lea (dl@cs.oswego.edu)
Date: Mon Oct 22 2001 - 18:18:53 EDT

Jerry wrote...

>> > Initially all variables are 0
>> > Thread 1
>> > Volatile1 = 1
>> > while (A == 0) {;}
>> >
>> > Thread 2
>> > while (Volatile1 != 1) {;}
>>> print "Success"
>>>

> I do not believe there is currently any such requirement in either the JLS
> or JVMS and I would strongly oppose adding one. Oracle's RDBMS Server VM
> has entirely non-preemptive scheduling. Once Thread 2 gets into its loop
> that is all the VM does. Thread 1 never runs.
>

Mostly as point of information, what would happen in your JVM if these were
written as:

Thread 1
   Volatile1 = 1
   while (A == 0) { Thread.yield(); }

Thread 2
   while (Volatile1 != 1) { Thread.yield(); }

The JLS allows the same behavior as without the yields. 

-- 
Doug Lea, Computer Science Department, SUNY Oswego, Oswego, NY 13126 USA
dl@cs.oswego.edu 315-312-2688 FAX:315-312-5424 http://gee.cs.oswego.edu/  
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