Instrument ThreadPoolExecutor and ForkJoinPool

[pkwarren]

The current instrumentation for ExecutorService doesn't expose several useful properties of subclasses which can be helpful when determining how to properly size an executor. The current instrumentation exposes the following:

• Meter: submitted, completed
• Counter: running
• Timer: idle, duration

Micrometer exposes quite a few additional properties of both ThreadPoolExecutor and ForkJoinPool: https://micrometer.io/docs/ref/jvm. It would be helpful to expose these in addition to the current metrics (in particular, the gauges for the number of threads, size of queued tasks, etc.)

[joschi]

@pkwarren I think this makes sense and would be a nice addition. 👍

Would you be able to provide a PR for this for Dropwizard Metrics 4.2.x?

[pkwarren]

Yep - I've been meaning to raise a PR to add this. Hope to get to it shortly.

[joschi]

@pkwarren Did you get any chance to start working on this?

[pkwarren]

@joschi - No I haven't. I'm not currently using DW at work and haven't had as much time as before for OSS work.

[joschi]

Closed via #1928