Java agents aren't (really) supported

[pron]

The -javaagent flag is passed to the JVM in java.cc, but the classpath is handled by RunJava. This is not how Java agents work!

The spec says this:

The agent class will be loaded by the system class loader (see ClassLoader.getSystemClassLoader).

I.e., the Java agent must see the classpath! It actually means more than that. The agent and the application share a class loader so they have access to the same static fields etc.

This results in a failure whenever a Java agent tries to access a class that is contained on the classpath, but not in the agent JAR.

A related problem is that the spec says:

The agent JAR is appended to the system class path.

But this isn't implemented.

[pron]

Actually, what happens is that the master context is used by the agent, and not the application's context, which is created by RunJava, which is launched after the agent.

This points the way to a possible fix: set up the isolated context in a java agent that is always passed first to the JVM.

[circlespainter]

Case:

• Clone and gradle install https://github.com/puniverse/capsule-osv
• Clone https://github.com/puniverse/photon/tree/capsule-osv
• Uncomment https://github.com/puniverse/photon/blob/capsule-osv/src/main/java/co/paralleluniverse/photon/Photon.java#L69 and https://github.com/puniverse/photon/blob/capsule-osv/src/main/java/co/paralleluniverse/photon/Photon.java#L89
• cd photon ; gradle osvCapsule ; java -Dcapsule.log=verbose -jar build/libs/photon.jar -duration 5 -minmax -rate 10 -stats http://www.google.co.il