RFR: 8203629: Produce events in the JDK without a dependency on jdk.jfr

[Alan Bateman]

On 19/06/2018 03:06, Erik Gahlin wrote:
> Hi,
>
> Could I have a review of an enhancement that will make it possible to 
> add JFR events to java.base, and possibly other modules in the JDK, 
> without a compile time dependency on jdk.jfr.
>
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8203629
>
> Webrev:
> http://cr.openjdk.java.net/~egahlin/8203629.0
>
> Testing:
> Tests in test/jdk/jdk/jfr
>
> The functionality is a prerequisite for an upcoming enhancement that 
> will add JFR events to the security libraries.
>
> In short, jdk.jfr.Event (located in jdk.jfr) extends 
> jdk.internal.event.Event (located in java.base). Metadata for events, 
> such as labels and descriptions, are added using a mirror event class 
> located in jdk.jfr module. If the fields of the mirror class and the 
> event class don't match an InternalError is thrown.
>
> To illustrate how the mechanism can be used, see the following example 
> (not meant to be checked in).
>
> http://cr.openjdk.java.net/~egahlin/8203629.example
>
> Since the implementation of jdk.internal.event.Event is empty, the JIT 
> will typically eliminate all traces of JFR functionality unless Flight 
> Recorder is enabled.
>
Adding a way to get events from java.base is good but I wonder if 
jdk.internal.event.Event could be cleaned up before you push this. It 
would be nice to have a class description and some minimal method 
descriptions too. Also all the methods are empty which makes me wonder 
if they should be abstract (as the class is abstract) or whether it 
should be an interface. Some of the method modifiers are in unusual 
order and it would be good to get those cleaned up too.

-Alan