I think [EMAIL PROTECTED] wrote:
>
> would like to ask a related question about something that is still very
> unclear to me: if multiple threads are calling run(), what happens? say a
> bunch of threads invoke run() on the same Rete object in the following
> order:
>
> thread 1 ->rete.run()
> thread 2 ->rete.run()
> thread 3 ->rete.run()
> ....
> thread N ->rete.run()
>
> could this result in an illegal system state if any of the run() calls
> overlap? could this crash Rete, or cause unexpected exceptions, etc.?
>
First: nothing bad can happen, guaranteed. There is a single mutex
that protects run(), run(int), and runUntilHalt() such that each
engine can only be running in one thread at a time. Other threads can
be simultaneously adding/removing facts, so they can be influencing
the agenda during the run.
As to the order in which the various threads would enter the run()
method: I'm actually not sure that the Java Language Spec requires
them to proceed in order -- i.e., just because they call run() in the
order 1, 2, 3 doesn't mean they'll get the lock in that
order. One common practice is to call runUntilHalt()in a dedicated
thread, so that the engine is always running; when there's no work to
do, it sleeps.
This was brought up recently here on this list; see
http://www.mail-archive.com/[email protected]/msg04691.html for
more information.
---------------------------------------------------------
Ernest Friedman-Hill
Distributed Systems Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
Org. 8920, MS 9012 [EMAIL PROTECTED]
PO Box 969 http://herzberg.ca.sandia.gov
Livermore, CA 94550
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