/*

 * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package javax.swing;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.*;

import java.util.concurrent.*;

import java.util.concurrent.locks.*;

import java.util.concurrent.atomic.AtomicLong;

import sun.awt.AppContext;

/**

 * Internal class to manage all Timers using one thread.

 * TimerQueue manages a queue of Timers. The Timers are chained

 * together in a linked list sorted by the order in which they will expire.

 *

 * @author Dave Moore

 * @author Igor Kushnirskiy

 */

class TimerQueue implements Runnable

{

    private static final Object sharedInstanceKey =

        new StringBuffer("TimerQueue.sharedInstanceKey");

    private static final Object expiredTimersKey =

        new StringBuffer("TimerQueue.expiredTimersKey");

    private final DelayQueue<DelayedTimer> queue;

    private volatile boolean running;

    private final Lock runningLock;

    /* Lock object used in place of class object for synchronization.

     * (4187686)

     */

    private static final Object classLock = new Object();

    /** Base of nanosecond timings, to avoid wrapping */

    private static final long NANO_ORIGIN = System.nanoTime();

    /**

     * Constructor for TimerQueue.

     */

    public TimerQueue() {

        super();

        queue = new DelayQueue<DelayedTimer>();

        // Now start the TimerQueue thread.

        runningLock = new ReentrantLock();

        startIfNeeded();

    }

    public static TimerQueue sharedInstance() {

        synchronized (classLock) {

            TimerQueue sharedInst = (TimerQueue)

                                    SwingUtilities.appContextGet(

                                                        sharedInstanceKey);

            if (sharedInst == null) {

                sharedInst = new TimerQueue();

                SwingUtilities.appContextPut(sharedInstanceKey, sharedInst);

            }

            return sharedInst;

        }

    }

    void startIfNeeded() {

        if (! running) {

            runningLock.lock();

            if (running) {

                return;

            }

            try {

                final ThreadGroup threadGroup = AppContext.getAppContext().getThreadGroup();

                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {

                    String name = "TimerQueue";

                    Thread timerThread =

                        new Thread(threadGroup, this, name, 0, false);

                    timerThread.setDaemon(true);

                    timerThread.setPriority(Thread.NORM_PRIORITY);

                    timerThread.start();

                    return null;

                });

                running = true;

            } finally {

                runningLock.unlock();

            }

        }

    }

    void addTimer(Timer timer, long delayMillis) {

        timer.getLock().lock();

        try {

            // If the Timer is already in the queue, then ignore the add.

            if (! containsTimer(timer)) {

                addTimer(new DelayedTimer(timer,

                                      TimeUnit.MILLISECONDS.toNanos(delayMillis)

                                      + now()));

            }

        } finally {

            timer.getLock().unlock();

        }

    }

    private void addTimer(DelayedTimer delayedTimer) {

        assert delayedTimer != null && ! containsTimer(delayedTimer.getTimer());

        Timer timer = delayedTimer.getTimer();

        timer.getLock().lock();

        try {

            timer.delayedTimer = delayedTimer;

            queue.add(delayedTimer);

        } finally {

            timer.getLock().unlock();

        }

    }

    void removeTimer(Timer timer) {

        timer.getLock().lock();

        try {

            if (timer.delayedTimer != null) {

                queue.remove(timer.delayedTimer);

                timer.delayedTimer = null;

            }

        } finally {

            timer.getLock().unlock();

        }

    }

    boolean containsTimer(Timer timer) {

        timer.getLock().lock();

        try {

            return timer.delayedTimer != null;

        } finally {

            timer.getLock().unlock();

        }

    }

    public void run() {

        runningLock.lock();

        try {

            while (running) {

                try {

                    DelayedTimer runningTimer = queue.take();

                    Timer timer = runningTimer.getTimer();

                    timer.getLock().lock();

                    try {

                        DelayedTimer delayedTimer = timer.delayedTimer;

                        if (delayedTimer == runningTimer) {

                            /*

                             * Timer is not removed (delayedTimer != null)

                             * or not removed and added (runningTimer == delayedTimer)

                             * after we get it from the queue and before the

                             * lock on the timer is acquired

                             */

                            timer.post(); // have timer post an event

                            timer.delayedTimer = null;

                            if (timer.isRepeats()) {

                                delayedTimer.setTime(now()

                                    + TimeUnit.MILLISECONDS.toNanos(

                                          timer.getDelay()));

                                addTimer(delayedTimer);

                            }

                        }

                        // Allow run other threads on systems without kernel threads

                        timer.getLock().newCondition().awaitNanos(1);

                    } catch (SecurityException ignore) {

                    } finally {

                        timer.getLock().unlock();

                    }

                } catch (InterruptedException ie) {

                    // Shouldn't ignore InterruptedExceptions here, so AppContext

                    // is disposed gracefully, see 6799345 for details

                    if (AppContext.getAppContext().isDisposed()) {

                        break;

                    }

                }

            }

        }

        catch (ThreadDeath td) {

            // Mark all the timers we contain as not being queued.

            for (DelayedTimer delayedTimer : queue) {

                delayedTimer.getTimer().cancelEvent();

            }

            throw td;

        } finally {

            running = false;

            runningLock.unlock();

        }

    }

    public String toString() {

        StringBuilder buf = new StringBuilder();

        buf.append("TimerQueue (");

        boolean isFirst = true;

        for (DelayedTimer delayedTimer : queue) {

            if (! isFirst) {

                buf.append(", ");

            }

            buf.append(delayedTimer.getTimer().toString());

            isFirst = false;

        }

        buf.append(")");

        return buf.toString();

    }

    /**

     * Returns nanosecond time offset by origin

     */

    private static long now() {

        return System.nanoTime() - NANO_ORIGIN;

    }

    static class DelayedTimer implements Delayed {

        // most of it copied from

        // java.util.concurrent.ScheduledThreadPoolExecutor

        /**

         * Sequence number to break scheduling ties, and in turn to

         * guarantee FIFO order among tied entries.

         */

        private static final AtomicLong sequencer = new AtomicLong(0);

        /** Sequence number to break ties FIFO */

        private final long sequenceNumber;

        /** The time the task is enabled to execute in nanoTime units */

        private volatile long time;

        private final Timer timer;

        DelayedTimer(Timer timer, long nanos) {

            this.timer = timer;

            time = nanos;

            sequenceNumber = sequencer.getAndIncrement();

        }

        public final long getDelay(TimeUnit unit) {

            return  unit.convert(time - now(), TimeUnit.NANOSECONDS);

        }

        final void setTime(long nanos) {

            time = nanos;

        }

        final Timer getTimer() {

            return timer;

        }

        public int compareTo(Delayed other) {

            if (other == this) { // compare zero ONLY if same object

                return 0;

            }

            if (other instanceof DelayedTimer) {

                DelayedTimer x = (DelayedTimer)other;

                long diff = time - x.time;

                if (diff < 0) {

                    return -1;

                } else if (diff > 0) {

                    return 1;

                } else if (sequenceNumber < x.sequenceNumber) {

                    return -1;

                }  else {

                    return 1;

                }

            }

            long d = (getDelay(TimeUnit.NANOSECONDS) -

                      other.getDelay(TimeUnit.NANOSECONDS));

            return (d == 0) ? 0 : ((d < 0) ? -1 : 1);

        }

    }

}