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package com.sun.grizzly.util;

import java.io.IOException;
import java.nio.channels.Selector;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Factory used to dispatch/share {@link Selector}.
 *
 * @author Scott Oaks
 * @author Jean-Francois Arcand
 * @author gustav trede
 */
public final class SelectorFactory {

    private static final int MISS_THRESHOLD = 10000;
    public static final int DEFAULT_MAX_SELECTORS = 20;
    /**
     * The number of {@link Selector} to create.
     */
    private static volatile int maxSelectors = DEFAULT_MAX_SELECTORS;
    /**
     * Cache of {@link Selector}
     */
    private final static Queue selectors =
            DataStructures.getCLQinstance(Selector.class);
    
    /**
     * The current number of Selectors in the pool.
     */
    private final static AtomicInteger poolSize = new AtomicInteger();

    /**
     * Number of times poll execution didn't find the available selector in the pool.
     */
    private final static AtomicInteger missesCounter = new AtomicInteger();

    /**
     * Set max selector pool size.
     * @param size max pool size
     */
    public static void setMaxSelectors(int size) {
        if (size < 0) {
            throw new IllegalArgumentException("size < 0");
        }

        missesCounter.set(0);
        maxSelectors = size;
    }

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

    /**
     * Please ensure to use try finally around get and return of selector so avoid leaks.
     * Get a exclusive {@link Selector}
     * @return {@link Selector}
     */
    public static Selector getSelector() {
        Selector selector = selectors.poll();

        if (selector != null) {
            poolSize.decrementAndGet();
        } else {
            try {
                selector = Utils.openSelector();
            } catch (IOException e) {
               LoggerUtils.getLogger().log(Level.WARNING,
                         "SelectorFactory. Can not create a selector", e);
            }
            
            final int missesCount = missesCounter.incrementAndGet();
            if (missesCount % MISS_THRESHOLD == 0) {
                LoggerUtils.getLogger().log(Level.WARNING,
                        "SelectorFactory. Pool encounters a lot of misses {0}. "
                        + "Increase default {1} pool size",
                        new Object[] {missesCount, maxSelectors});
            }
        }

        return selector;
    }

    /**
     * Please ensure to use try finally around get and return of selector so avoid leaks.
     * Return the {@link Selector} to the cache
     * @param s {@link Selector}
     */
    public static void returnSelector(Selector s) {
        if (poolSize.getAndIncrement() < maxSelectors) {
            selectors.offer(s);
        } else {
            poolSize.decrementAndGet();
            closeSelector(s);
        }
    }

    /**
     * Executes Selector.selectNow() and returns
     * the {@link Selector} to the cache
     */
    public static void selectNowAndReturnSelector(Selector s) {
        try {
            s.selectNow();
            returnSelector(s);
        } catch (IOException e) {
            Logger logger = LoggerUtils.getLogger();
            logger.log(Level.WARNING,
                    "Unexpected problem when releasing temporary Selector", e);
            
            closeSelector(s);
        }
    }

    private static void closeSelector(Selector s) {
        try {
            s.close();
        } catch (IOException ignored) {
            // We are not interested
        }
    }
}