RFR: 8238665: Add JFR event for direct memory statistics

[Denghui Dong]

Hi,

> On Mar 18, 2020, at 11:46 PM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
> 
> 
> On 13/03/2020 14:54, Denghui Dong wrote:
>> Good suggestion, moved.
>> Webrev: http://cr.openjdk.java.net/~ddong/8238665/webrev.03/ <http://cr.openjdk.java.net/~ddong/8238665/webrev.03/>
> This looks much better.
> 
> What would you think about renaming the JFR event to "DirectBufferStatistics"? The concern I have with the proposed naming is that it will be really awkward to extend it to support mapped buffers.

It’s ok for me.

> 
> The implementation changes look okay, hopefully Erik will skim over them. One small suggestion for for ManagementFactoryHelper is that you can stream().collect(Collectors.toList()) to create the value for bufferPools. You could even change it to volatile so that getBufferMXBeans isn't a synchronized method.
> 

Make sense, updated.

Webrev: http://cr.openjdk.java.net/~ddong/8238665/webrev.04/ <http://cr.openjdk.java.net/~ddong/8238665/webrev.04/>

@Erik, could you help review it?


> -Alan.

Denghui Dong