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package javax.swing.text;

import java.util.Vector;
import sun.awt.AppContext;

A queue of text layout tasks.
Author:
 Timothy Prinzing
See Also:
AsyncBoxView
Since:
  1.3/**
 * A queue of text layout tasks.
 *
 * @author  Timothy Prinzing
 * @see     AsyncBoxView
 * @since   1.3
 */
public class LayoutQueue {

    private static final Object DEFAULT_QUEUE = new Object();

    private Vector<Runnable> tasks;
    private Thread worker;

    
Construct a layout queue.
/**
     * Construct a layout queue.
     */
    public LayoutQueue() {
        tasks = new Vector<Runnable>();
    }

    
Fetch the default layout queue.
/**
     * Fetch the default layout queue.
     */
    public static LayoutQueue getDefaultQueue() {
        AppContext ac = AppContext.getAppContext();
        synchronized (DEFAULT_QUEUE) {
            LayoutQueue defaultQueue = (LayoutQueue) ac.get(DEFAULT_QUEUE);
            if (defaultQueue == null) {
                defaultQueue = new LayoutQueue();
                ac.put(DEFAULT_QUEUE, defaultQueue);
            }
            return defaultQueue;
        }
    }

    
Set the default layout queue.
Params:
q – the new queue./**
     * Set the default layout queue.
     *
     * @param q the new queue.
     */
    public static void setDefaultQueue(LayoutQueue q) {
        synchronized (DEFAULT_QUEUE) {
            AppContext.getAppContext().put(DEFAULT_QUEUE, q);
        }
    }

    
Add a task that is not needed immediately because
the results are not believed to be visible.
/**
     * Add a task that is not needed immediately because
     * the results are not believed to be visible.
     */
    public synchronized void addTask(Runnable task) {
        if (worker == null) {
            worker = new LayoutThread();
            worker.start();
        }
        tasks.addElement(task);
        notifyAll();
    }

    
Used by the worker thread to get a new task to execute
/**
     * Used by the worker thread to get a new task to execute
     */
    protected synchronized Runnable waitForWork() {
        while (tasks.size() == 0) {
            try {
                wait();
            } catch (InterruptedException ie) {
                return null;
            }
        }
        Runnable work = tasks.firstElement();
        tasks.removeElementAt(0);
        return work;
    }

    
low priority thread to perform layout work forever
/**
     * low priority thread to perform layout work forever
     */
    class LayoutThread extends Thread {

        LayoutThread() {
            super("text-layout");
            setPriority(Thread.MIN_PRIORITY);
        }

        public void run() {
            Runnable work;
            do {
                work = waitForWork();
                if (work != null) {
                    work.run();
                }
            } while (work != null);
        }


    }

}