package jutil;

/**
 * Base class for all threads that need to be
 * safely stopped, paused, and unpaused.
 */
public class WorkerThread extends Thread {
	/**
	 * set to true to stop the thread.
	 */
	private boolean stop = false;
	/**
	 * set to true to pause the thread
	 */
	private boolean pause = false;
	/**
	 * An ID generator.
	 */
	private static int nextID = 0;
	/**
	 * This threads id number.
	 */
	private int id;
	/**
	 * Set to true to see diagnostics
	 */
	public boolean DEBUG = true;
	public WorkerThread(String name, int id) {
		super(name);
		this.id = id;
	}
	public WorkerThread(int id) {
		this("Worker thread " + id, id);
	}
	public WorkerThread(String name) {
		this(name, nextID++);
	}
	public WorkerThread() {
		this(nextID++);
	}
	public boolean isPaused() { return pause; }
	public boolean isStopped() { return stop; }

	/**
	 * Safely halt this thread.
	 */
	synchronized public void halt() { stop = true; }
	/**
	 * Safely pause this thread
	 */
	synchronized public void pause() { pause = true; }
	/**
	 * Safely unpause this thread.
	 */
	synchronized public void unpause() { notifyAll(); }
	/**
	 * Override this method with the basic thread task.
	 * @return true if it wants to be called again, false otherwise
	 */
	protected boolean task() {
		if (DEBUG) System.out.println(getName() + " is performing its task");
		return false;
	}
	/**
	 * repeatedly calls the task method until the thread is stopped or the
	 * task method returns false.
	 */
	public void run() {
		while(true) {
			synchronized(this) {
				if (stop) break;
				if (pause) {
					if (DEBUG) System.out.println(getName() + " is pausing");
					try {
						wait();
						if (DEBUG) System.out.println(getName() + " is resuming");
						pause = false;
					} catch(InterruptedException ie) {
						System.err.println(ie.getMessage());
					}
				}
			}
			if (!task()) { stop = true; break;}
			try {
				sleep(100); // be cooperative
			} catch(InterruptedException ie) {
				System.err.println(ie.getMessage());
			}
		} // while
		if (DEBUG) System.out.println(getName() + " is shutting down");
	}
}