RFR (M): 8207266: ThreadMXBean::getThreadAllocatedBytes() can be quicker for self thread

[Mandy Chung]

On 9/18/19 5:00 PM, Hohensee, Paul wrote:
> They all implement com.sun.management.ThreadMXBean, so adding a getCurrentThreadAllocatedBytes broke them. Potential fix is to give it a default implementation, vis
>
>      public default long getCurrentThreadAllocatedBytes() {
>          return -1;
>      }
>

com.sun.management.ThreadMXBean (and other platform MXBeans) is a 
"sealed" interface which should only be implemented by JDK. 
Unfortunately we don't have the sealed type feature yet.  Yes it needs 
to be a default method.  I think it should throw UOE.

      * @implSpec
      * The default implementation throws {@code 
UnsupportedOperationException}.

The @throw UOE can make it clear that it does not support current thread 
memory allocation measurement.

Mandy