RFR: 8241001: Improve logging in the ConcurrentGCBreakpoint mechanism

[Per Liden]

On 3/19/20 5:41 AM, Kim Barrett wrote:
> Please review this change to the logging output produced by the
> ConcurrentGCBreakpoint facility.
> 
> Most of its log messages provide low-level information for someone
> debugging the breakpoint mechanism or a test using it, with relatively
> cryptic messages unless that is what one is doing.  As such, putting
> these messages at the debug level generates too much uninformative
> clutter for the fairly common case of gc*=debug logging; those
> messages have been demoted to the trace level.
> 
> There were logging messages for the concurrent cycle start
> (idle->active) and end (active->idle) transitions, which were
> duplicative of other logging messages from the normal concurrent cycle
> operation.  Those logging messages have been removed.  However, the
> message for the active->idle transition when there is an active run-to
> request has been retained, but the message text has been improved.
> 
> gc+breakpoint logging has also been configured to produce the normal
> "GC(n)" prefix, for those log messages produced by the collector.
> User requests such as run-to don't (and can't) have that prefix, as
> they don't occur within the context of the collection but instead come
> from Java threads outside the collector.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8241001
> 
> Webrev:
> https://cr.openjdk.java.net/~kbarrett/8241001/open.00/

Looks good!

/Per

> 
> Testing:
> Locally (linux-x64) ran TestConcurrentGCBreakpoints.java with various
> logging options and verified the results were as described.
> 
>