<AWT Dev> numAppContexts in AppContext modified in not-thread-safe way.

[Clemens Eisserer]

Hi David,

The original code is rather strange. The static field will be default
> initialized to zero, the AppContext constructor will increment it to 1, then
> the static block explicitly sets it to one.
> It would be cleaner/clearer if the field were declared and initialized
> before the static block.
>
Agreed. Please find the modified patch at:
http://cr.openjdk.java.net/~ceisserer/7080700/webrev.04/


That's an uninteresting case from a data-race perspective though because the
> counter is only ever written once.
>
In the constructor the non-atomic increment can cause a missed update and
therefor cause numAppContexts to become 1 or even 0, which could trigger
that logic unintentionally.


However I now wonder about how often this gets called in a Swing app? If
> this is a frequent call then the overhead of the atomic might be
> significant. Perhaps the Swing folk should be evaluating this change as
> well?

Did some benchmarks,  and at least on x86 AtomicInteger.get() performs
identical to a volatile field read.


Thanks, Clemens
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