RFR: 8071507: (ref) Clear phantom reference as soft and weak references do

[Peter Levart]

On 12/04/2015 08:16 AM, Per Liden wrote:
>
> test/java/lang/ref/PhantomReferentClearing.java:
>
>   85         // Delete root -> O1, collect, verify P1 notified, P2 not 
> notified.
>   86         O1 = null;
>   87         System.gc();
>   88         if (Q1.remove(ENQUEUE_TIMEOUT) == null) {
>   89             throw new RuntimeException("P1 not notified by O1 
> deletion");
>   90         } else if (Q2.remove(ENQUEUE_TIMEOUT) != null) {
>   91             throw new RuntimeException("P2 notified by O1 
> deletion.");
>   92         }
>   93
>   94         // Delete root -> O2, collect. P2 should be notified.
>   95         O2 = null;
>   96         System.gc();
>   97         if (Q2.remove(ENQUEUE_TIMEOUT) == null) {
>   98             throw new RuntimeException("P2 not notified by O2 
> deletion");
>   99         }
>
> The calls to System.gc() isn't guaranteed to do what the test expects 
> here. As you know, System.gc(), might not actually do anything, 
> depending on which collector is used and the current circumstances (GC 
> locker held, a concurrent GC is already in process, etc). To make the 
> test robust I'd suggest you call System.gc() and check the queue in a 
> loop, and fail after some reasonable amount of time/iterations.

Whether you poll the queue for some time T or you remove from queue with 
timeout of T, it doesn't matter. The Reference(s) are enqueued by a 
ReferenceHandler thread and the thread waiting in remove() will get 
notified when a reference gets enqueued...

Regards, Peter

>
> cheers,
> /Per
>
>> http://cr.openjdk.java.net/~kbarrett/8071507/hotspot.05/
>>
>> Testing:
>> jprt, aurora ad hoc (defaults, GC/Runtime nightly, JCK)
>>