RFR: Use one future

[Alan Bateman]

On Wed, 13 Apr 2022 23:25:28 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

> Here's an example of changing the structured task scope impls, using one `Future` field and comparing future states. In effect the state can only increase monotonically (as per the order determined by the comparator).
> 
> The single future field could be made non-volatile, using the `VarHandle` for the volatile read in `handleComplete` since the happens-before edge should ensure the future is visible to the reading thread after `join`.

Clever!

src/jdk.incubator.concurrent/share/classes/jdk/incubator/concurrent/StructuredTaskScope.java line 801:

> 799:     }
> 800: 
> 801:     private static int stateToId(Future.State s) {

Did you mean to to name this stateToId or stateToInt? 
Style-wise I guess I'd would align the arrows but it doesn't matter.

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Marked as reviewed by alanb (Committer).

PR: https://git.openjdk.java.net/loom/pull/144