Toy application that demonstrates the java.util.concurrent.ExecutorCompletionService

CompletionServiceExample.java

import java.util.Random;
import java.util.concurrent.*;

/**
 * App that tests completion service.
 */
public class CompletionServiceExample {

    private static final int COUNT = 25;

    public static void main(String[] args) {

        ExecutorService executor = Executors.newFixedThreadPool(3);
        CompletionService<String> cs = new ExecutorCompletionService<String>(executor);

        for(int i = 0; i < COUNT; i++) {
            final int taskno = i + 1;
            cs.submit(new Callable<String>() {
                @Override
                public String call() throws Exception {
                    long secondsToSleep = 1000 * (new Random().nextInt(4) + 1);
                    Thread.sleep(secondsToSleep);
                    return "Task #" + taskno + " slept " +
                            TimeUnit.SECONDS.convert(secondsToSleep, TimeUnit.MILLISECONDS) + " seconds.";
                }
            });
        }

        executor.shutdown();

        int remaining = COUNT;
        while(remaining > 0) {

            String result;
            try {
                result = cs.take().get();
                System.out.println("*** " + result);
            } catch (InterruptedException e) {
                System.err.println("Interrupted when " + remaining + " task(s) were left: " + e.getMessage());
                System.err.println("Aborting...");
                break;
            } catch (ExecutionException e) {
                // Remember that ExecutionException wraps the root cause.
                System.err.println("Could not get result: " + e.getCause().getMessage());
            }

            remaining--;
        }

        System.out.println("*** DONE ***");
    }


}