Example thread pool that pulls tasks from a Supplier

PullingPool.java

import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Supplier;

// Example of a thread pool that pulls tasks from a Supplier
public class PullingPool {

    public static void main(String[] args) throws Exception {
        final int nThreads = (int) (Math.random() * 4) + 2;
        final int nTasks = (int) (Math.random() * 45) + 5;
        final AtomicInteger supplierId = new AtomicInteger(nTasks);
        final String marker = "****** ";

        System.out.println(marker + "Running " + nTasks + " tasks with " + nThreads + " threads");

        // Supplier of tasks, will be called by the thread pool,
        // returns null if no more tasks to run
        final Supplier<Callable> supplier = () -> {
            final int id = supplierId.decrementAndGet();
            if (id < 0) {
                // we're done
                return null;
            }
            return new Callable() {
                @Override
                public Object call() throws Exception {
                    final int wait = (int) (Math.random() * 250);
                    Thread.sleep(wait);
                    return String.format("%s (%d msec)", id, wait);
                }
            };
        };

        // Thread pool, each thread loops until the task supplier returns a null Callable
        for (int i = 0; i < nThreads; i++) {
            final int id = i;
            final AtomicInteger executed = new AtomicInteger();
            new Thread(() -> {
                while (true) {
                    try {
                        final Callable task = supplier.get();
                        if (task == null) {
                            System.out.println(marker + "Thread " + id + ": done, ran " + executed.get() + " tasks");
                            break;
                        }
                        System.out.println("Thread " + id + " ran task " + task.call());
                        executed.incrementAndGet();
                    } catch (Exception whatShallWeDo) {
                        whatShallWeDo.printStackTrace();
                    }
                }
            }).start();
        }
    }
}