/*
 * "hello world" program, version 1
 *
 * creates threads using anonymous inner class implementing Runnable.
 *
 * environment variable NUM_THREADS specifies number of threads.
 */
public class Hello1 {

    public static void main(String[] args) {

        /* get number of threads from environment variable */

        int numThreads = 0;
        try {
            String s = System.getenv("NUM_THREADS");
            if (s == null) {
                numThreads = 1;
            }
            else {
                numThreads = Integer.parseInt(s);
            }
        }
        catch (NumberFormatException e) {
            System.out.println("non-numeric value for NUM_THREADS");
            System.exit(1);
        }

        /* create threads */

        Thread[] threads = new Thread[numThreads];

        for (int i = 0; i < numThreads; ++i) {
            threads[i] = new Thread(new Runnable() {
                public void run() {
                    System.out.println("hello, world, from thread " + 
                        Thread.currentThread().getName());
                }
            });
        }

        /* start them up */

        System.out.println("starting threads");

        for (int i = 0; i < numThreads; ++i) {
            threads[i].start();
        }

        /* wait for them to finish */

        for (int i = 0; i < numThreads; ++i) {
            try {
                threads[i].join();
            }
            catch (InterruptedException e) {
                System.err.println("this should not happen");
            }
        }

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

    }
}