//
// Very simple program demonstrating the use of threads.
//
// Command-line argument is P (number of threads).
//
// Synchronization via class (static) method.
//

// ---- class containing main program --------------------------------

public class ThreadsHello2 {

    public static void main(String[] args) {

	if (args.length < 1) {
	    System.err.println("Usage:  java ThreadsHello2 numThreads");
	    System.exit(1);
	}

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

	Thread [] threads = new Thread[P];

	// Create threads.
	for (int i = 0; i < P; ++i)
	    threads[i] = new Thread(new Hello2Thread(i));

	// Start them up.
	for (int i = 0; i < P; ++i)
	    threads[i].start();

	// Wait for them to finish.
	try {
	    for (int i = 0; i < P; ++i)
		threads[i].join();
	} catch (InterruptedException e) {
	    // should never happen
	}

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

// ---- class for threads --------------------------------------------

// We'll have one object of this class for each thread.
// It holds the data needed by the thread, plus the code.

class Hello2Thread implements Runnable {

    // Instance variable (like C++ member variable).
    private int myID;

    // Constructor.
    public Hello2Thread(int myID) {
	this.myID = myID;
    }

    // Class method (like C++ static member function).
    private static synchronized void printMsg(int ID) {
	System.out.print("hello, world, ");
	System.out.println("from thread " + ID);
    }

    // Instance method (like C++ member function).
    // This one implements run() in Runnable interface to define
    //   behavior of thread using this object.
    public void run() {
	printMsg(myID);
    }
}