/* 
 *  Generic example of master/worker program with dynamic assignment of
 *  tasks to workers.  (The point of this example is to demonstrate use
 *  of tags.)  "Tasks" just consist of sleeping for a specified
 *  time; times to wait are generatedly randomly from 0 to a specified
 *  maximum.
 *
 *  Command-line arguments:  total tasks, maximum wait time, number of threads
 */
public class MasterWorker {

    /* variables/constants to be used by all threads */

    private static int totalTasks;
    private static int maxWait;
    private static int nThreads;
    private static int minCount = -1;
    private static int maxCount = -1;
    private static int minTime = -1;
    private static int maxTime = -1;
    private static java.util.Random randGenerator = new java.util.Random();
    private static int tasksAssigned = 0;

    /* main method (also serves as master) */

    public static void main(String[] args) {

        /* process command-line argument */
        if (args.length < 3) {
            System.err.println("usage:  MasterWorker totalTasks maxWait nThreads");
            System.exit(1);
        }
        try {
            totalTasks = Integer.parseInt(args[0]);
            maxWait = Integer.parseInt(args[1]);
            nThreads = Integer.parseInt(args[2]);
        }
        catch (NumberFormatException e) {
            System.err.println("usage:  MasterWorker totalTasks maxWait nThreads");
            System.exit(1);
        }

        /* start timing */
        long startTime = System.currentTimeMillis();

        /* create threads */
        Thread[] threads = new Thread[nThreads];
        for (int i = 0; i < threads.length; ++i) {
            threads[i] = new Thread(new CodeForThread(i));
        }

        /* start them up */
        for (int i = 0; i < threads.length; ++i) {
            threads[i].start();
        }

        /* wait for them to finish */
        for (int i = 0; i < threads.length; ++i) {
            try {
                threads[i].join();
            }
            catch (InterruptedException e) {
                System.err.println("this should not happen");
            }
        }

        /* print results */
        System.out.println("task count ranged from " + minCount + " to " +
                maxCount);
        System.out.println("time ranged from " + minTime + " to " +
                maxTime);
    }

    /* method to "get something from the bag of tasks" -- returns -1
     * when no more to get
     */

    private static synchronized int getTask() {
        if (++tasksAssigned <= totalTasks) 
            return randGenerator.nextInt(maxWait);
        else
            return -1;
    }

    /* method to update min, max counts */

    private static synchronized void updateMinMax(int workerCount, 
            int workerTime) {
        if ((workerCount < minCount) || (minCount < 0)) 
            minCount = workerCount;
        if (workerCount > maxCount) 
            maxCount = workerCount;
        if ((workerTime < minTime) || (minTime < 0)) 
            minTime = workerTime;
        if (workerTime > maxTime) 
            maxTime = workerTime;
    }

    /* static inner class to contain code to run in each thread */

    private static class CodeForThread implements Runnable {

        private int myID;

        public CodeForThread(int myID) {
            this.myID = myID;
        }

        public void run() {
            int taskCount = 0;
            int totalWorkTime = 0;
            int workAmount = 0;
            while ((workAmount = getTask()) >= 0) {
                System.out.println("worker " + myID + " received " +
                        workAmount);
                ++taskCount;
                totalWorkTime += workAmount;
                try {
                    Thread.sleep(workAmount);
                }
                catch (InterruptedException e) {
                    System.err.println("this should not happen");
                }
            }
            System.out.println("worder " + myID + " done");
            updateMinMax(taskCount, totalWorkTime);
        }
    }
}