/*

 * Copyright (c) 2000, 2013, 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 sun.awt;

import java.awt.AWTEvent;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.HashSet;

import java.util.IdentityHashMap;

import java.util.Map;

import java.util.Set;

import sun.misc.InnocuousThread;

import sun.util.logging.PlatformLogger;

import sun.awt.util.ThreadGroupUtils;

/**

 * This class is to let AWT shutdown automatically when a user is done

 * with AWT. It tracks AWT state using the following parameters:

 * <ul>

 * <li><code>peerMap</code> - the map between the existing peer objects

 *     and their associated targets

 * <li><code>toolkitThreadBusy</code> - whether the toolkit thread

 *     is waiting for a new native event to appear in its queue

 *     or is dispatching an event

 * <li><code>busyThreadSet</code> - a set of all the event dispatch

 *     threads that are busy at this moment, i.e. those that are not

 *     waiting for a new event to appear in their event queue.

 * </ul><p>

 * AWT is considered to be in ready-to-shutdown state when

 * <code>peerMap</code> is empty and <code>toolkitThreadBusy</code>

 * is false and <code>busyThreadSet</code> is empty.

 * The internal AWTAutoShutdown logic secures that the single non-daemon

 * thread (<code>blockerThread</code>) is running when AWT is not in

 * ready-to-shutdown state. This blocker thread is to prevent AWT from

 * exiting since the toolkit thread is now daemon and all the event

 * dispatch threads are started only when needed. Once it is detected

 * that AWT is in ready-to-shutdown state this blocker thread waits

 * for a certain timeout and if AWT state doesn't change during timeout

 * this blocker thread terminates all the event dispatch threads and

 * exits.

 */

public final class AWTAutoShutdown implements Runnable {

    private static final AWTAutoShutdown theInstance = new AWTAutoShutdown();

    /**

     * This lock object is used to synchronize shutdown operations.

     */

    private final Object mainLock = new Object();

    /**

     * This lock object is to secure that when a new blocker thread is

     * started it will be the first who acquire the main lock after

     * the thread that created the new blocker released the main lock

     * by calling lock.wait() to wait for the blocker to start.

     */

    private final Object activationLock = new Object();

    /**

     * This set keeps references to all the event dispatch threads that

     * are busy at this moment, i.e. those that are not waiting for a

     * new event to appear in their event queue.

     * Access is synchronized on the main lock object.

     */

    private final Set<Thread> busyThreadSet = new HashSet<>(7);

    /**

     * Indicates whether the toolkit thread is waiting for a new native

     * event to appear or is dispatching an event.

     */

    private boolean toolkitThreadBusy = false;

    /**

     * This is a map between components and their peers.

     * we should work with in under activationLock&mainLock lock.

     */

    private final Map<Object, Object> peerMap = new IdentityHashMap<>();

    /**

     * References the alive non-daemon thread that is currently used

     * for keeping AWT from exiting.

     */

    private Thread blockerThread = null;

    /**

     * We need this flag to secure that AWT state hasn't changed while

     * we were waiting for the safety timeout to pass.

     */

    private boolean timeoutPassed = false;

    /**

     * Once we detect that AWT is ready to shutdown we wait for a certain

     * timeout to pass before stopping event dispatch threads.

     */

    private static final int SAFETY_TIMEOUT = 1000;

    /**

     * Constructor method is intentionally made private to secure

     * a single instance. Use getInstance() to reference it.

     *

     * @see     AWTAutoShutdown#getInstance

     */

    private AWTAutoShutdown() {}

    /**

     * Returns reference to a single AWTAutoShutdown instance.

     */

    public static AWTAutoShutdown getInstance() {

        return theInstance;

    }

    /**

     * Notify that the toolkit thread is not waiting for a native event

     * to appear in its queue.

     *

     * @see     AWTAutoShutdown#notifyToolkitThreadFree

     * @see     AWTAutoShutdown#setToolkitBusy

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    public static void notifyToolkitThreadBusy() {

        getInstance().setToolkitBusy(true);

    }

    /**

     * Notify that the toolkit thread is waiting for a native event

     * to appear in its queue.

     *

     * @see     AWTAutoShutdown#notifyToolkitThreadFree

     * @see     AWTAutoShutdown#setToolkitBusy

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    public static void notifyToolkitThreadFree() {

        getInstance().setToolkitBusy(false);

    }

    /**

     * Add a specified thread to the set of busy event dispatch threads.

     * If this set already contains the specified thread or the thread is null,

     * the call leaves this set unchanged and returns silently.

     *

     * @param thread thread to be added to this set, if not present.

     * @see     AWTAutoShutdown#notifyThreadFree

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    public void notifyThreadBusy(final Thread thread) {

        if (thread == null) {

            return;

        }

        synchronized (activationLock) {

            synchronized (mainLock) {

                if (blockerThread == null) {

                    activateBlockerThread();

                } else if (isReadyToShutdown()) {

                    mainLock.notifyAll();

                    timeoutPassed = false;

                }

                busyThreadSet.add(thread);

            }

        }

    }

    /**

     * Remove a specified thread from the set of busy event dispatch threads.

     * If this set doesn't contain the specified thread or the thread is null,

     * the call leaves this set unchanged and returns silently.

     *

     * @param thread thread to be removed from this set, if present.

     * @see     AWTAutoShutdown#notifyThreadBusy

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    public void notifyThreadFree(final Thread thread) {

        if (thread == null) {

            return;

        }

        synchronized (activationLock) {

            synchronized (mainLock) {

                busyThreadSet.remove(thread);

                if (isReadyToShutdown()) {

                    mainLock.notifyAll();

                    timeoutPassed = false;

                }

            }

        }

    }

    /**

     * Notify that the peermap has been updated, that means a new peer

     * has been created or some existing peer has been disposed.

     *

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    void notifyPeerMapUpdated() {

        synchronized (activationLock) {

            synchronized (mainLock) {

                if (!isReadyToShutdown() && blockerThread == null) {

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

                        activateBlockerThread();

                        return null;

                    });

                } else {

                    mainLock.notifyAll();

                    timeoutPassed = false;

                }

            }

        }

    }

    /**

     * Determine whether AWT is currently in ready-to-shutdown state.

     * AWT is considered to be in ready-to-shutdown state if

     * <code>peerMap</code> is empty and <code>toolkitThreadBusy</code>

     * is false and <code>busyThreadSet</code> is empty.

     *

     * @return true if AWT is in ready-to-shutdown state.

     */

    private boolean isReadyToShutdown() {

        return (!toolkitThreadBusy &&

                 peerMap.isEmpty() &&

                 busyThreadSet.isEmpty());

    }

    /**

     * Notify about the toolkit thread state change.

     *

     * @param busy true if the toolkit thread state changes from idle

     *             to busy.

     * @see     AWTAutoShutdown#notifyToolkitThreadBusy

     * @see     AWTAutoShutdown#notifyToolkitThreadFree

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    private void setToolkitBusy(final boolean busy) {

        if (busy != toolkitThreadBusy) {

            synchronized (activationLock) {

                synchronized (mainLock) {

                    if (busy != toolkitThreadBusy) {

                        if (busy) {

                            if (blockerThread == null) {

                                activateBlockerThread();

                            } else if (isReadyToShutdown()) {

                                mainLock.notifyAll();

                                timeoutPassed = false;

                            }

                            toolkitThreadBusy = busy;

                        } else {

                            toolkitThreadBusy = busy;

                            if (isReadyToShutdown()) {

                                mainLock.notifyAll();

                                timeoutPassed = false;

                            }

                        }

                    }

                }

            }

        }

    }

    /**

     * Implementation of the Runnable interface.

     * Incapsulates the blocker thread functionality.

     *

     * @see     AWTAutoShutdown#isReadyToShutdown

     */

    public void run() {

        Thread currentThread = Thread.currentThread();

        boolean interrupted = false;

        synchronized (mainLock) {

            try {

                /* Notify that the thread is started. */

                mainLock.notifyAll();

                while (blockerThread == currentThread) {

                    mainLock.wait();

                    timeoutPassed = false;

                    /*

                     * This loop is introduced to handle the following case:

                     * it is possible that while we are waiting for the

                     * safety timeout to pass AWT state can change to

                     * not-ready-to-shutdown and back to ready-to-shutdown.

                     * In this case we have to wait once again.

                     * NOTE: we shouldn't break into the outer loop

                     * in this case, since we may never be notified

                     * in an outer infinite wait at this point.

                     */

                    while (isReadyToShutdown()) {

                        if (timeoutPassed) {

                            timeoutPassed = false;

                            blockerThread = null;

                            break;

                        }

                        timeoutPassed = true;

                        mainLock.wait(SAFETY_TIMEOUT);

                    }

                }

            } catch (InterruptedException e) {

                interrupted = true;

            } finally {

                if (blockerThread == currentThread) {

                    blockerThread = null;

                }

            }

        }

        if (!interrupted) {

            AppContext.stopEventDispatchThreads();

        }

    }

    @SuppressWarnings("serial")

    static AWTEvent getShutdownEvent() {

        return new AWTEvent(getInstance(), 0) {

        };

    }

    /**

     * Creates and starts a new blocker thread. Doesn't return until

     * the new blocker thread starts.

     *

     * Must be called with {@link sun.security.util.SecurityConstants#MODIFY_THREADGROUP_PERMISSION}

     */

    private void activateBlockerThread() {

        Thread thread;

        String name =  "AWT-Shutdown";

        if (System.getSecurityManager() == null) {

            thread = new Thread(ThreadGroupUtils.getRootThreadGroup(), this, name);

        } else {

            thread = new InnocuousThread(this, name);

        }

        thread.setContextClassLoader(null);

        thread.setDaemon(false);

        blockerThread = thread;

        thread.start();

        try {

            /* Wait for the blocker thread to start. */

            mainLock.wait();

        } catch (InterruptedException e) {

            System.err.println("AWT blocker activation interrupted:");

            e.printStackTrace();

        }

    }

    void registerPeer(final Object target, final Object peer) {

        synchronized (activationLock) {

            synchronized (mainLock) {

                peerMap.put(target, peer);

                notifyPeerMapUpdated();

            }

        }

    }

    void unregisterPeer(final Object target, final Object peer) {

        synchronized (activationLock) {

            synchronized (mainLock) {

                if (peerMap.get(target) == peer) {

                    peerMap.remove(target);

                    notifyPeerMapUpdated();

                }

            }

        }

    }

    Object getPeer(final Object target) {

        synchronized (activationLock) {

            synchronized (mainLock) {

                return peerMap.get(target);

            }

        }

    }

    void dumpPeers(final PlatformLogger aLog) {

        if (aLog.isLoggable(PlatformLogger.Level.FINE)) {

            synchronized (activationLock) {

                synchronized (mainLock) {

                    aLog.fine("Mapped peers:");

                    for (Object key : peerMap.keySet()) {

                        aLog.fine(key + "->" + peerMap.get(key));

                    }

                }

            }

        }

    }

} // class AWTAutoShutdown