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/*
 * ===========================================
 * Java Pdf Extraction Decoding Access Library
 * ===========================================
 *
 * Project Info:  http://www.idrsolutions.com
 * Help section for developers at http://www.idrsolutions.com/support/
 *
 * (C) Copyright 1997-2017 IDRsolutions and Contributors.
 *
 * This file is part of JPedal/JPDF2HTML5
 *
 @LICENSE@
 *
 * ---------------
 * SwingWorker.java
 * ---------------
 */
package org.jpedal.utils;

public abstract class SwingWorker {
    private Object value;  // see getValue(), setValue()
    //private Thread thread;

    /**
     * Class to maintain reference to current worker thread
     * under separate synchronization control.
     */
    private static class ThreadVar {
        private Thread thread;

        ThreadVar(final Thread t) {
            thread = t;
        }

        synchronized Thread get() {
            return thread;
        }

        synchronized void clear() {
            thread = null;
        }
    }

    final ThreadVar threadVar;

    /**
     * Get the value produced by the worker thread, or null if it
     * hasn't been constructed yet.
     */
    protected synchronized Object getValue() {
        return value;
    }

    /**
     * Set the value produced by worker thread
     */
    private synchronized void setValue(final Object x) {
        value = x;
    }

    /**
     * Compute the value to be returned by the get method.
     */
    public abstract Object construct();

    /**
     * A new method that interrupts the worker thread.  Call this method
     * to force the worker to stop what it's doing.
     */
    public void interrupt() {
        final Thread t = threadVar.get();
        if (t != null) {
            t.interrupt();

            while (t.isAlive()) {
                try {
                    Thread.sleep(20);
                } catch (final InterruptedException e) {
                    LogWriter.writeLog("Exception: " + e.getMessage());
                }
            }
        }
        threadVar.clear();
    }

    /**
     * Return the value created by the construct method
     * Returns null if either the constructing thread or the current
     * thread was interrupted before a value was produced
     *
     * @return the value created by the construct method
     */
    public Object get() {
        while (true) {
            final Thread t = threadVar.get();
            if (t == null) {
                return getValue();
            }
            try {
                t.join();
            } catch (final InterruptedException e) {

                LogWriter.writeLog("Exception in handling thread " + e);

                Thread.currentThread().interrupt(); // propagate
                return null;
            }
        }
    }


    /**
     * Start a thread that will call the construct method
     * and then exit.
     */
    public SwingWorker() {

        final Runnable doConstruct = new Runnable() {
            @Override
            public void run() {
                try {
                    setValue(construct());

                } catch (final Exception e) {
                    LogWriter.writeLog("Caught a Exception " + e);
                } finally {
                    threadVar.clear();
                }
            }
        };

        final Thread t = new Thread(doConstruct);
        t.setDaemon(true);
        threadVar = new ThreadVar(t);
    }

    /**
     * Start the worker thread.
     */
    public void start() {
        final Thread t = threadVar.get();
        if (t != null) {
            t.start();
        }
    }
}