JEP 271: Unified GC Logging - First pre-review

[Bengt Rutisson]

Hi again everyone,

An update on the work for JEP 271 Unified GC Logging.

I now have a working prototype that covers all GCs. Here are some 
examples comparing the old format (using -XX:+PrintGC and 
-XX:+PrintGCDetails) with the new format (using -Xlog):

http://cr.openjdk.java.net/~brutisso/JEP-271/pre-review.00/compare.html

The new logging format, using -Xlog, is much more flexible than the old 
format. So, the comparison table on the above page is by no means 
complete. I hope it will give a good overview, but to get a real feel 
for how the new logging works I think it is necessary to run locally and 
play around with the logging options.

Here is a webrev of the changes so far:
http://cr.openjdk.java.net/~brutisso/JEP-271/pre-review.00/webrev.00/

There is still work to do and I have some known issues with the code 
changes. So, I am currently not asking for too much feedback on the 
actual code changes. I am more looking for feedback on the logging 
behavior. The webrev can be useful to get a feel for what the code 
changes will look like but mostly I think it can be used to apply the 
patch and build your own HotSpot to try out the new logging.

Some changes based on the initial feedback:
- Start and end timestamps for the GC included on the GC log line.
- Printing the unit of a value without a space. I.e. "10.345ms" instead 
of "10.345 ms". (Still working on fixing this in all places as well as 
trying to use milliseconds instead of seconds in as many places as 
possible.)
- Printing heap change information with a fixed unit. I am now using M 
for overall heap transition and K for detailed information on the debug 
level.
- Removed the "summary" tag. Instead the end logging for a GC includes 
all relevant information.

All feedback is very welcome!

Thanks,
Bengt