/*

 * Copyright 2006 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package sun.net.httpserver;

import java.util.*;

import java.nio.*;

import java.net.*;

import java.io.*;

import java.security.*;

import java.nio.channels.*;

/*

 * Implements a cache of java.nio.channels.Selector

 * where Selectors are allocated on demand and placed

 * in a temporary cache for a period of time, so they

 * can be reused. If a period of between 2 and 4 minutes

 * elapses without being used, then they are closed.

 */

public class SelectorCache {

    static SelectorCache cache = null;

    private SelectorCache () {

        freeSelectors = new LinkedList<SelectorWrapper>();

        CacheCleaner c = AccessController.doPrivileged(

            new PrivilegedAction<CacheCleaner>() {

            public CacheCleaner run() {

                CacheCleaner cleaner = new CacheCleaner();

                cleaner.setDaemon (true);

                return cleaner;

            }

        });

        c.start();

    }

    /**

     * factory method for creating single instance

     */

    public static SelectorCache getSelectorCache () {

        synchronized (SelectorCache.class) {

            if (cache == null) {

                cache = new SelectorCache ();

            }

        }

        return cache;

    }

    private static class SelectorWrapper {

        private Selector sel;

        private boolean deleteFlag;

        private SelectorWrapper (Selector sel) {

            this.sel = sel;

            this.deleteFlag = false;

        }

        public Selector getSelector() { return sel;}

        public boolean getDeleteFlag () {return deleteFlag;}

        public void setDeleteFlag (boolean b) {deleteFlag = b;}

    }

    /* list of free selectors. Can be re-allocated for a period

     * of time, after which if not allocated will be closed

     * and removed from the list (by CacheCleaner thread)

     */

    LinkedList<SelectorWrapper> freeSelectors;

    synchronized Selector getSelector () throws IOException {

        SelectorWrapper wrapper = null;

        Selector selector;

        if (freeSelectors.size() > 0) {

            wrapper = freeSelectors.remove();

            selector = wrapper.getSelector();

        } else {

            selector = Selector.open();

        }

        return selector;

    }

    synchronized void freeSelector (Selector selector) {

        freeSelectors.add (new SelectorWrapper (selector));

    }

    /* Thread ensures that entries on freeSelector list

     * remain there for at least 2 minutes and no longer

     * than 4 minutes.

     */

    class CacheCleaner extends Thread {

        public void run () {

            long timeout = ServerConfig.getSelCacheTimeout() * 1000;

            while (true) {

                try {Thread.sleep (timeout); } catch (Exception e) {}

                synchronized (freeSelectors) {

                    ListIterator<SelectorWrapper> l = freeSelectors.listIterator();

                    while (l.hasNext()) {

                        SelectorWrapper w = l.next();

                        if (w.getDeleteFlag()) {

                            /* 2nd pass. Close the selector */

                            try {

                                w.getSelector().close();

                            } catch (IOException e) {}

                            l.remove();

                        } else {

                            /* 1st pass. Set the flag */

                            w.setDeleteFlag (true);

                        }

                    }

                }

            }

        }

    }

}