melix / jmh-gradle-plugin / 152

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Pull #153

travis-ci

Adapt JMH plugin to work with chnages to classpath/classloader in workers in 5.5

Before 5.5, the classpath used to start a worker daemon was a flattened combination
of the Gradle runtime, the worker runnable (and dependencies), and the additional
classpath (which is the benchmark classes + dependencies). This differed from how
the classpath was structured when worker runnables run inside the Gradle daemon.

In 5.5, we changed the worker process to start with a "minimum" class path. This
includes only the Gradle runtime necessary to get work over to the worker process.
Once in the worker process, a separate classloader is created (following the pattern
of classloader isolation in the Gradle daemon). This change should have been transparent
to the worker runnable, except...

In the JMH IsolatedRunner, we create a JMH Runner, pass it some options and call run().
JMH uses the java.class.path system property to derive the classpath of the benchmark.
In 5.5, java.class.path is the classpath of the worker process and nothing else, so JMH
fails quickly due to missing classes.

This change fixes the IsolatedRunner to recreate the classpath expected by JMH and sets
java.class.path before running JMH. The classpath passed to JMH is now only JMH and the
benchmark. It no longer contains the entire Gradle runtime or worker related classes.

This change also removes ExtensionOptions and SerializableOptions because this required
the JMH plugin classes to be passed to the benchmark as well.  We now build a JMH Options
and pass that over to the worker instead.

I suspect that there are still some other lurking issues:
- Embedded benchmark execution probably doesn't work.  I'm not sure if it ever did.
- The benchmark jar shouldn't need to be on the worker classpath
- The benchmark jar doesn't appear to be up-to-date safe
- It's a little weird that we need to use process isolation to run the benchmark, but
  this looks like a missing feature in Gradle and a lack of conf... (continued)

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