<p>Any ideas how to determine the number of active threads currently running in an <a href="https://docs.oracle.com/javase/9/docs/api/java/util/concurrent/ExecutorService.html" rel="noreferrer"><code>ExecutorService</code></a>?</p>

Use a
ThreadPoolExecutor
implementation and call
getActiveCount()
on it:
```
```
int getActiveCount() 
// Returns the approximate number of threads that are actively executing tasks.
```
```
The ExecutorService interface does not provide a method for that, it depends on the implementation.