RFR: 8278581: Improve reference processing statistics log output

[Albert Mingkun Yang]

On Sat, 11 Dec 2021 15:04:43 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> The first commit renames `Cleared` to `Dropped` and added `Processed` in the log output.
> 
> The second commit compressed the log output into one line per ref-type. The final log format looks like:
> 
> 
> [11.803s][debug][gc,phases,ref  ] GC(0)   SoftReference Discovered: 0, Dropped: 0, Processed: 0
> [11.803s][debug][gc,phases,ref  ] GC(0)   WeakReference Discovered: 1147, Dropped: 752, Processed: 395
> [11.803s][debug][gc,phases,ref  ] GC(0)   FinalReference Discovered: 0, Dropped: 0, Processed: 0
> [11.803s][debug][gc,phases,ref  ] GC(0)   PhantomReference Discovered: 242, Dropped: 2, Processed: 240
> 
> 
> Test: hotspot_gc

Thanks for the review.

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PR: https://git.openjdk.java.net/jdk/pull/6806