SelectorFactory.java

/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the License).  You may not use this file except in
 * compliance with the License.
 *
 * You can obtain a copy of the license at
 * https://glassfish.dev.java.net/public/CDDLv1.0.html or
 * glassfish/bootstrap/legal/CDDLv1.0.txt.
 * See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL
 * Header Notice in each file and include the License file
 * at glassfish/bootstrap/legal/CDDLv1.0.txt.
 * If applicable, add the following below the CDDL Header,
 * with the fields enclosed by brackets [] replaced by
 * you own identifying information:
 * "Portions Copyrighted [year] [name of copyright owner]"
 *
 * Copyright 2007 Sun Microsystems, Inc. All rights reserved.
 */
package com.google.code.hs4j.network.util;

import java.io.IOException;
import java.nio.channels.Selector;
import java.util.EmptyStackException;
import java.util.Stack;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;



/**
 * Temp selector factory,come from grizzly
 * 
 * @author dennis zhuang
 */
public class SelectorFactory {

    public static final int DEFAULT_MAX_SELECTORS = 20;

    private static final Logger logger = LoggerFactory.getLogger(SelectorFactory.class);
    /**
     * The timeout before we exit.
     */
    public final static long timeout = 5000;

    /**
     * The number of <code>Selector</code> to create.
     */
    private static int maxSelectors;

    /**
     * Cache of <code>Selector</code>
     */
    private final static Stack<Selector> selectors = new Stack<Selector>();

    /**
     * Creates the <code>Selector</code>
     */
    static {
        try {
            setMaxSelectors(DEFAULT_MAX_SELECTORS);
        }
        catch (IOException ex) {
            logger.warn("SelectorFactory initializing Selector pool", ex);
        }
    }


    /**
     * Set max selector pool size.
     * 
     * @param size
     *            max pool size
     */
    public final static void setMaxSelectors(int size) throws IOException {
        synchronized (selectors) {
            if (size < maxSelectors) {
                reduce(size);
            }
            else if (size > maxSelectors) {
                grow(size);
            }

            maxSelectors = size;
        }
    }


    /**
     * Returns max selector pool size
     * 
     * @return max pool size
     */
    public final static int getMaxSelectors() {
        return maxSelectors;
    }


    /**
     * Get a exclusive <code>Selector</code>
     * 
     * @return <code>Selector</code>
     */
    public final static Selector getSelector() {
        synchronized (selectors) {
            Selector s = null;
            try {
                if (selectors.size() != 0) {
                    s = selectors.pop();
                }
            }
            catch (EmptyStackException ex) {
            }

            int attempts = 0;
            try {
                while (s == null && attempts < 2) {
                    selectors.wait(timeout);
                    try {
                        if (selectors.size() != 0) {
                            s = selectors.pop();
                        }
                    }
                    catch (EmptyStackException ex) {
                        break;
                    }
                    attempts++;
                }
            }
            catch (InterruptedException ex) {
            }
            return s;
        }
    }


    /**
     * Return the <code>Selector</code> to the cache
     * 
     * @param s
     *            <code>Selector</code>
     */
    public final static void returnSelector(Selector s) {
        synchronized (selectors) {
            selectors.push(s);
            if (selectors.size() == 1) {
                selectors.notify();
            }
        }
    }


    /**
     * Increase <code>Selector</code> pool size
     */
    private static void grow(int size) throws IOException {
        for (int i = 0; i < size - maxSelectors; i++) {
            selectors.add(Selector.open());
        }
    }


    /**
     * Decrease <code>Selector</code> pool size
     */
    private static void reduce(int size) {
        for (int i = 0; i < maxSelectors - size; i++) {
            try {
                Selector selector = selectors.pop();
                selector.close();
            }
            catch (IOException e) {
                logger.error("SelectorFactory.reduce", e);
            }
        }
    }

}