/*
 * Copyright (c) 2005, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.imageio.stream;

import sun.awt.util.ThreadGroupUtils;

import java.io.IOException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Set;
import java.util.WeakHashMap;
import javax.imageio.stream.ImageInputStream;

This class provide means to properly close hanging
image input/output streams on VM shutdown.
This might be useful for proper cleanup such as removal
of temporary files.
Addition of stream do not prevent it from being garbage collected
if no other references to it exists. Stream can be closed
explicitly without removal from StreamCloser queue.
Explicit removal from the queue only helps to save some memory.
/**
 * This class provide means to properly close hanging
 * image input/output streams on VM shutdown.
 * This might be useful for proper cleanup such as removal
 * of temporary files.
 *
 * Addition of stream do not prevent it from being garbage collected
 * if no other references to it exists. Stream can be closed
 * explicitly without removal from StreamCloser queue.
 * Explicit removal from the queue only helps to save some memory.
 */
public class StreamCloser {

    private static WeakHashMap<CloseAction, Object> toCloseQueue;
    private static Thread streamCloser;

    public static void addToQueue(CloseAction ca) {
        synchronized (StreamCloser.class) {
            if (toCloseQueue == null) {
                toCloseQueue =
                    new WeakHashMap<CloseAction, Object>();
            }

            toCloseQueue.put(ca, null);

            if (streamCloser == null) {
                final Runnable streamCloserRunnable = new Runnable() {
                    public void run() {
                        if (toCloseQueue != null) {
                            synchronized (StreamCloser.class) {
                                Set<CloseAction> set =
                                    toCloseQueue.keySet();
                                // Make a copy of the set in order to avoid
                                // concurrent modification (the is.close()
                                // will in turn call removeFromQueue())
                                CloseAction[] actions =
                                    new CloseAction[set.size()];
                                actions = set.toArray(actions);
                                for (CloseAction ca : actions) {
                                    if (ca != null) {
                                        try {
                                            ca.performAction();
                                        } catch (IOException e) {
                                        }
                                    }
                                }
                            }
                        }
                    }
                };

                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    /* The thread must be a member of a thread group
                     * which will not get GCed before VM exit.
                     * Make its parent the top-level thread group.
                     */
                    ThreadGroup tg = ThreadGroupUtils.getRootThreadGroup();
                    streamCloser = new Thread(tg, streamCloserRunnable,
                                              "StreamCloser", 0, false);
                    /* Set context class loader to null in order to avoid
                     * keeping a strong reference to an application classloader.
                     */
                    streamCloser.setContextClassLoader(null);
                    Runtime.getRuntime().addShutdownHook(streamCloser);
                    return null;
                });
            }
        }
    }

    public static void removeFromQueue(CloseAction ca) {
        synchronized (StreamCloser.class) {
            if (toCloseQueue != null) {
                toCloseQueue.remove(ca);
            }
        }
    }

    public static CloseAction createCloseAction(ImageInputStream iis) {
        return new CloseAction(iis);
    }

    public static final class CloseAction {
        private ImageInputStream iis;

        private CloseAction(ImageInputStream iis) {
            this.iis = iis;
        }

        public void performAction() throws IOException {
            if (iis != null) {
                iis.close();
            }
        }
    }
}