Updates to JEP-158: JVM Unified Logging are coming...

[Fredrik Arvidsson]

Hi

We are planning to release an updated version of JEP-158 very soon. The 
work to update this JEP has been going on for some time and we now feel 
we are ready to present it to a wider audience.

The JEP for JVM Unified Logging was created back in February 2012. The 
requirements for the API and implementation were heavily influenced by 
the logging functionality in JRockit JVM. The JEP was updated and 
refined in mid 2014 and eventually targeted for JDK 9 in late 2014:
https://bugs.openjdk.java.net/browse/JDK-8046148

During the review process of the JEP some concerns were voiced about the 
chosen API and functionality but the conclusion was that the proposal 
would work, and the JEP was targeted for JDK 9 and the implementation 
work was started.

Early 2015 during pre-reviews and presentations of the API and 
implementation concerns were again raised about the formulation of the 
JEP, this time with greater force. At this point we decided to take a 
time-out and investigate our options going forward.

The time-out led to a modified proposal that can be found here:
http://cr.openjdk.java.net/~farvidsson/JEP-158/JEP-158.html
and with some illustrations here:
http://cr.openjdk.java.net/~farvidsson/JEP-158/JEP-158_Illustration.png

So what have we changed, and why?
In short we have switched from using an hierarchical log subject layout 
to something that could be best described as a tag based solution.

The main reason for the change of the logging API is that we have found 
that some logging can't easily be ordered under a single hierarchical 
subject but can belong to multiple subjects/areas. One example of this 
is logging in the 'metaspace' code. The functionality in the 'metaspace 
area' can be called from both GC and Runtime code. Another example is 
class-unloading. There are more examples on this of course, but these 
two we think are very clear and easy to understand.

The core functionality of the logging framework is not changed that much 
from the earlier proposal. We have tried to make it leaner and not as 
verbose (functionality wise) as before. The scope of the implementation 
has been narrowed down some to enable us to deliver good value as soon 
as possible.

Our plan is as follows:
After getting initial feedback from the community about the new proposal 
we will update the JEP description. We aim to do this early next week.
We are planning to use the JDK9 sandbox repository during development. 
This enables us who are implementing it to work in an efficient way and 
at the same time it allows any interested party to try out and follow 
the work during the implementation phase.

More information about the sandbox repository name and other 
practicalities will follow shortly.

Cheers
Fredrik Arvidsson & Marcus Larsson, JVM Serviceability, Stockholm.