Re: JavaMemoryModel: No decision on lost notifications

From: Bill Pugh (
Date: Wed Aug 06 2003 - 15:00:46 EDT

At 9:05 AM -0400 8/6/03, Doug Lea wrote:
>Part of the problem here is that we still have trouble saying exactly
>where the contoversy lies. Here's a stab at it, but I suspect that
>even this folmulation itself may be controversial.
>I see this as two distinct issues.
>A. When one thread, t, does a wait -- for completeness, assume a timed wait,
> mon.wait(msecs)
>there is in intrinsic race among the following ways for the wait to return:
> 1. Some thread invokes mon.notify, and thread t was chosen
> 2. Some thread invokes mon.notifyAll
> 3. Some thread invokes t.interrupt
> 4. The wait times out
> 5. The wait spuriously returns
>The choices for governing this are:
> A1. Must an implementation ensure that if causes (3), (4), or (5) have
> already occurred (at some hypothetical instant), that cause (1) does
> NOT also occur? Or,
> A2. Are multiple/indeterminate causes allowed?
>The main question here is whether choice A1 is actually implementable
>(without exorbitant cost/overhead) on all the platforms Java runs on.

Since you can't determine whether a thread returned from wait because
it was notified, timed out, or spuriously returned, I don't think you
need to worry about lost notifications in those cases.

However, you can distinguish the cases where a call to wait returned
by throwing IE, and the path for handling that case is typically
different than the case for handling normal returns from wait.


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