FRF: Wiring GC events to JFR

[Aleksey Shipilev]

On 08/27/2018 04:28 PM, Zhengyu Gu wrote:
> http://cr.openjdk.java.net/~zgu/shenandoah/gc_messages/webrev.00/

This looks okay-ish. I would probably try and make a macro-generator for those strings, but current
version is good enough for now.

> http://cr.openjdk.java.net/~zgu/shenandoah/jfr-event-1/webrev.00/

*) The introduction of GCTraceConcTime means it changes our logging, right? For example, it would
print "Concurrent marking" without "gc+start", right? This is inconvenient and makes the logs noisy.
Why do we need that change?

*) The comment is oddly formatted, and it seems "JMC" -> "JFR" is in order? Suggestion:

   // FIXME: It seems that JFR throws away level 0 events, which are the Shenandoah
   // pause events. Create this pseudo level 0 event to push real events to level 1

Thanks,
-Aleksey