/*
 * "hello world" program, version 4:
 *
 * uses java.util.concurrent ExecutorService to start threads and assign 
 * them work, another way.
 *
 * command-line argument specifies number of threads.
 */
package csci3366.sample.hello;
import csci3366.sample.utility.Utility;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;

public class Hello4 {

    public static void main(String[] args) {

        /* get number of threads from command line */

        int numThreads = Utility.getIntegerArg(args, 0, 1, 
                "numThreads", "arguments:  numThreads");

        /* create executor for threads */

        ExecutorService executor = Executors.newFixedThreadPool(numThreads);

        /* 
         * create tasks and send to executor, creating Future objects so we 
         * can wait for tasks to finish 
         */

        Future<?>[] results = new Future<?>[numThreads]; 

        for (int i = 0; i < results.length; ++i) {
            results[i] = executor.submit(new Inner(i));
        }

        /* shut down executor and wait for threads to finish */

        executor.shutdown();
        for (int i = 0; i < results.length; ++i) {
            try {
                /* get() returns a value, but we aren't using it */
                results[i].get(); 
            }
            catch (ExecutionException e) {
                System.err.println("should not happen");
            }
            catch (InterruptedException e) {
                System.err.println("should not happen");
            }
        }

        System.out.println("threads all done");

    }

    /* inner class containing code for each thread to execute */

    private static class Inner implements Runnable {

        private int myID;

        public Inner(int myID_) {
            myID = myID_;
        }

        public void run() {
            System.out.println("hello from " + myID);
        }

    }
}