Example with Java 8 Lamdbam executors and futures

Lambdastuff.java

package lamdbastuff;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.Semaphore;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;

public class Lamdbastuff {

    static int failed;
    static boolean debug = false;
    
    static Callable<String> longRunningTask(Semaphore s, int i) {
        return () -> {
            final long start = System.currentTimeMillis();
            boolean permit = false;
            try {
                permit = s.tryAcquire(350, TimeUnit.MILLISECONDS);
                TimeUnit.MILLISECONDS.sleep(ThreadLocalRandom.current().nextInt(10, 25));
                if (permit) {
                    TimeUnit.MILLISECONDS.sleep(ThreadLocalRandom.current().nextInt(50, 250));
                } else {
                    failed++;
                }
            } catch (InterruptedException e) {
                throw new IllegalStateException(e);
            } finally {
                if (permit) {
                    s.release();
                }
            }
            return "Task " + i + (permit ? " was executed and took " : " was NOT executed but took ") + (System.currentTimeMillis() - start) + " msec";
        };
    }
        
    public static void main(String args[]) throws Exception {
        ExecutorService executor = Executors.newFixedThreadPool(10);
        Semaphore semaphore = new Semaphore(3);
        final List<Future<String>> fut = new ArrayList<>();
        IntStream.range(0, 10).forEach(i -> fut.add(executor.submit(longRunningTask(semaphore, i))));
        
        while(!fut.isEmpty()) {
            for(Iterator<Future<String>> it = fut.iterator() ; it.hasNext() ; ) {
                Future<String> f = it.next();
                if(f.isDone()) {
                    System.out.println(f.get());
                    it.remove();
                }
            }
            TimeUnit.MILLISECONDS.sleep(100);
        }
        
        System.out.println("failed=" + failed);
        executor.shutdown();
    }
}