Review Request for 6878481: Add performance counters in the JDK

[Alan Bateman]

Andrew John Hughes wrote:
> :
> The use of synchronized at present seems flawed as only the set
> methods are protected and not the get.  So lb.get could be called
> while in an lb.put call.  I don't see the reason for using a
> LongBuffer either, as only index 0 is ever used.  Why not use an
> AtomicLong?
>   
The LongBuffer is a direct buffer with a reference to memory in the 
PerfData instrumentation buffer. This is the shared memory that jvmstat 
clients (jstat, VisualVM , ..) will attach to in order to monitor the VM.

> What is the purpose of d3dAvailable?  I don't know this piece of code
> so I'm not sure what it's counting, but it will presumably be zero
> forever on non-Windows systems.
>   
Mandy can say more about this, but it essentially allows jstat to see if 
the target VM is using the D3D pipeline or not.

-Alan.