Within the resources menu of FusionReactor, you can view each active thread within the JVM from either the Threads or Thread Visualizer view.
The threads view will list each thread and its current state, whereas the Thread visualizer will give you a graphical representation of the threads changing state over a 60 second period.
These views allow you to spot:
Blocked threads
Long-running processes on threads
Background tasks using excessive resource
For each thread, you have the ability to:
Stack trace and see what the thread is doing
Profile the thread to see what it executes over a 60 second period
Pause and debug the thread
Kill the thread if it is stuck (with inbuilt protection to not cause issues)