RE: JavaMemoryModel: Waits, Interrupts and Notify-s

From: David Holmes (
Date: Mon May 26 2003 - 18:09:27 EDT

Sylvia Else wrote:
> // Thread 3 may have now reached its wait call.
> // Interrupt thread 1. If thread 1 was woken up
> // above, but will throw Interrupted
> // Exception as a result of this call,
> // then thread 2 must be woken up - not
> // thread 3!
> t1.interrupt();

Right. t3 wasn't in the wait-set when the original notification came
in so it shouldn't get any late notification. That violates the
non-observable property that I claimed should hold. :(

I find myself wearing two hats on this one.

As a programmer I really would like a nice clean well-defined
programming model for wait/notify/interrupt such that reasonable
experiments (like the above - use of yield() notwithstanding :) ) work
as expected. It certainly makes writing TCK tests for this easier -
otherwise how the heck do you write a test for any of this stuff. ;-)
And it would follow the POSIX approach which has a very clearly
defined programming model that talks about events that block and
unblock threads - both notification and interrupt (signals and
cancellation) unblock a thread and so that thread can't be involved in
any later action on the wait-set/condition-variable.

But I can see the implementation issues for the VM with trying to
conform with this nice clean programming model. If it were trivial to
fix then I think it would be fixed.


David Holmes

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