//
// Very simple program demonstrating the use of threads.
//
// Command-line argument is P (number of threads).
//
// Synchronization via class (static) method.
//
// (This version is functionally identical to ThreadsHello2
//    but is meant to be more Java-esque.)
//

// ---- Class containing main program --------------------------------

public class ThreadsHello3 {

    private int nThreads;

    // Constructor.
    public ThreadsHello3(int P) {
	nThreads = P;
    }

    // Method to do the intended work.
    public void greet() {

	// Create objects for threads.
	Hello3[] objs = new Hello3[nThreads];
	for (int i = 0; i < nThreads; ++i) 
	    objs[i] = new Hello3(i);

	// Create threads, start them up, and wait for them to finish.
	ThreadManager tMgr = new ThreadManager(objs);
	tMgr.start();
	tMgr.join();
    }

    // Main method.
    public static void main(String[] args) {

	if (args.length < 1) {
	    System.err.println("Usage:  java ThreadsHello3 numThreads");
	    System.exit(1);
	}

	int P = Integer.parseInt(args[0]);

	ThreadsHello3 obj = new ThreadsHello3(P);

	obj.greet();

	System.out.println("That's all, folks!");
    }
}

// ---- Class to contain data and code for each thread ---------------

class Hello3 implements Runnable {

    private int myID;

    // Constructor.
    public Hello3(int myID) {
	this.myID = myID;
    }

    // Defines behavior of thread using this object --
    //   invoked by "start()" on thread.
    public void run() {
	printMsg(myID);
    }

    // Prints "hello" message.
    // "synchronized" keyword for class method means only one
    //   thread at a time can execute this method.
    private static synchronized void printMsg(int ID) {
	System.out.print("hello, world, ");
  	// pointless pause, included to make the effects of 
  	//   synchronization (or lack thereof) more obvious
	pause(1);
	System.out.println("from thread " + ID);
    }

    // Sleeps for n milliseconds.
    private static void pause(int n) {
	try {
	    Thread.sleep(n);
	}
	catch (InterruptedException e) { 
	     // should never happen
	}
   }
}