Fixes in monitoring, enable monitoring in Embedded GlassFish

[OndroMih]

Ensures that the reported current thread count and busy thread count is exactly the number of threads reported by the pool. Even if monitoring is started while thread pool is actively processing requests.

A few improvements in Embedded GlassFish to enable monitoring and access it via JMX (it was completely broken before):

• if the flashlight-agent is already loaded, don't attempt to load it - that would fail on newer Java versions
• concatenate probe-provider-class-names MANIFEST elements from dependencies, using gmaven plugin script at build time. It references all probes that should be activated

Embedded GlassFish requires running with flashlight-agent on command line with -javaagent:flashlight-agent.jar on newer Java versions as it doesn't contain the agent. Dynamic loading of agent is not a good practice with newer Java versions anyway.

When started with command "enable-monitoring --mbean true", metric will be available via JMX beans:

Example to start Embedded GlassFish with thread pool and http service metrics:

java -javaagent:/path/to/flashlight-agent.jar -jar glassfish-embedded-all.jar 'enable-monitoring --modules thread-pool:http-service'

Or, alternatively, using the following properties in glassfish.properties in the current directory:

configs.config.server-config.monitoring-service.module-monitoring-levels.thread-pool=HIGH
configs.config.server-config.monitoring-service.module-monitoring-levels.http-service=HIGH

And command:

java -javaagent:/path/to/flashlight-agent.jar -jar glassfish-embedded-all.jar

Then in VisualVM (with MBeans extension), in the amx node:

If you don't see the amx node, you need to execute the bootAMX operation from VisualVM first (the added test demonstrates how to do that in code):

[dmatej]

I would prefer using java and exec plugin; not sure if it is doable.
The groovy is not so well readable for us and we tend to do evil things: catching exceptions without processing them, closing jars just when their processing doesn't throw exceptions instead of try-with ...

[OndroMih]

I was lazy here and asked AI. It couldn't figure out how to do it using Ant. It kept suggesting using exec plugin with a shell script, which obviously wouldn't work on Windows. Then I decided to use Groovy, which works everywhere. Another option would be to create a new maven plugin, but that would have to be a separate project, or part of the buildhelper plugin, which is external and we would have to release it first.

Another option is to create a script in Java and execute it via the exec plugin, maybe that's what you mean. If we can compile it first or execute it directly as a script, then it should work too.

[OndroMih]

I tried. It's just too complicated. Groovy script is the best option. The only other option is to create a separate maven plugin, because we need to set a maven project property, which is used in another plugin to build the final MANIFEST. And I don't want to bother with a separate Maven plugin. The Groovy script is almost like Java and it's pretty simple.