[armedbear-devel] Franz-style Gates implementation

[Mark Evenson]

Erik Huelsmann wrote:
[…]
>>> I'm not particularly good at writing multiprocessing, or Java code. So
>>> please review carefully.
>> Tobias wrote this to support his version of a multi-threaded SLIME backend,
>> and has proposed it for inclusion in ABCL.
>>
>> When I get some time, I'll do some tests, but post the patch here in case it
>> helps someone else out before that time or if their is any feedback.
> 
> Well, I had a look at it this afternoon and from my reading, Tobias
> does really understand how to write Java and ABCL/Java code. I didn't
> see any particular issues with the code, but any testing before
> committing will be highly appreciated, of course.

 From my experience yesterday, I agree with your sentiments about the 
code (maybe some people are just born gifted!): the code works well, and 
smooths the threaded implementation of SLIME considerably (from a 
subjective point of view).

The one thing that bothers me is that apparently in Java, a thread in 
wait() can be woken up via so-called "spurious wakeups", i.e. no thread 
holding the object monitor that a wait() is called on has actually 
called notify() or notifyAll().  So, it is recommended (in the 
[documentation for java.lang.Thread.wait(timeout)][1]), that the 
following sort of code be used

     synchronized(object) {
       while (<condition does not hold>) {
         object.wait(timeout);
       }
     }

[1]: 
http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html#wait%28long%29

but this seems seems like it would defeat the notion of specifying a 
timeout in the first place (i.e. as long as the condition did not hold), 
object.wait(timeout) would continue to be invoked).  An explanation by 
someone of what I am not getting here would be helpful.

And there's the matter of testing, for which I would actually like to 
contribute unit tests that test the gates behavior.  But coming up with 
tests for multi-threaded scenarios is a bit tough as well.

Anyways, I plan to commit the Gates implementation to trunk now.

Mark


-- 
"A screaming comes across the sky.  It has happened before, but there
is nothing to compare to it now."