On 19/05/2017 12:28, Andrew Dinn wrote:
:
I don't think history is the most important guide here (whatever the
history might be). If agent support was not optional in the past that is
no reason to not make it optional now.
My reason for bringing up the history is to make it clear that the
standard tooling APIs have always been optional ("always" = JSR-163 /
Java SE 5). A clarification was needed in Java SE 8 to fix an oversight.
We haven't changed anything for Java SE 9.
To me it is not a problem that agent operation may be optional. What
matters is
i) it is still possible to choose to include agent support in an image
There are a number of pieces to this.
The biggest part is the JVM TI support that is compiled into libjvm. The
Oracle JDK downloads include the server VM and the minimal VM. The
former has the serviceability support compiled in, the minimal VM does
not. When using `jlink` then you would need to go out of your way to
specify `--vm=minimal` to exclude the server VM.
For java agent support then you need a java.base/libjvm that includes
JVM TI and you additionally need to ask `jlink` to include the
`java.instrument` module. There are several improvements that could be
done here to ensure that you don't accidentally create a run-time image
with java.instrument but no libjvm with JVM TI support, ditto for the
management modules that need instrumentation in the VM.
Another part is the java agent itself. It would be be nice to be able to
deploy a java agent as a module so that it can be specified to `jlink`.
We had to punt on this for Java SE 9 / JDK 9 but it's definitely
something to come back to in the future (only so much that we could take
on here in one release).
:
Does the tooling define specific image configuratons? Is there an
opportunity/need here to define and make visible a standard image format
('instrumentable') which comprises minimal + java.instrument?
Do you mean an aggregator module? Possible although I think `jlink`
usages are better suited to recipes, esp. when getting into some of the
trade-offs.
-Alan
