/**
  * Copyright (c): Uwe Schmidt, FH Wedel
  *
  * You may study, modify and distribute this source code
  * FOR NON-COMMERCIAL PURPOSES ONLY.
  * This copyright message has to remain unchanged.
  *
  * Note that this document is provided 'as is',
  * WITHOUT WARRANTY of any kind either expressed or implied.
  */

public class CountPrimes
    extends Thread {

    long lb, ub;
    long max;
    int noOfPrimes;

    CountPrimes child;

    public CountPrimes(long lb, long ub, long max) {
	super("CountPrimes(" + lb + "," + ub + ")");

	System.out.println("creating thread " + getName());

	this.lb  = lb;
	this.ub  = ub;
	this.max = max;

	splitWorkload();
    }

    public void run() {
	System.out.println(getName() + " is running");

	startChild();
	doOwnWork();
	waitForChild();

	System.out.println(getName() + " has finished");
    }

    private void splitWorkload() {
	if (ub - lb > max) {

	    long splitAt = lb + max;

	    child   = new CountPrimes(splitAt, ub, max);

	    ub      = splitAt;
	} else {
	    child   = null;
	}
    }

    private void startChild() {
	if (child != null) {
	    child.start();
	}
    }

    private void doOwnWork() {
	System.out.println(getName() + " is working");


	for (long i = lb; i < ub; ++i) {
	    if (isPrime(i))
		++noOfPrimes;
	}

	System.out.println(getName() + " has done own work");
    }

    private void waitForChild() {
	if (child != null) {
	    System.out.println(getName() + " is waiting for child");

	    try {
		child.join();
	    }
	    catch (InterruptedException e) {
	    }

	    System.out.println(getName() + " child has joined");

	    noOfPrimes += child.noOfPrimes;
	}
    }

    private boolean isPrime(long n) {
	long i = 2;
	if (n <= 1)
	    return false;

	while ( n % i != 0 && i * i <= n)
	    ++i;

	return i * i > n;
    }
}