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 package com.sun.grizzly.util;

 import com.sun.grizzly.Controller;

 import java.io.IOException;

 import java.nio.channels.Selector;

 import java.util.EmptyStackException;

 import java.util.Stack;

 import java.util.logging.Level;

 import java.util.logging.Logger;

 /**

  * Factory used to dispatch/share {@link Selector}.

  *

  * @author Scott Oaks

  * @author Jean-Francois Arcand

  */

 public class SelectorFactory{

     public static final int DEFAULT_MAX_SELECTORS = 20;

     /**

      * The timeout before we exit.

      */

     public static long timeout = 5000;

     /**

      * The number of {@link Selector} to create.

      */

     private static int maxSelectors = DEFAULT_MAX_SELECTORS;

     /**

      * Cache of {@link Selector}

      */

     private final static Stack<Selector> selectors = new Stack<Selector>();

     /**

      * have we created the Selector instances.

      */

     private static boolean initialized = false;

     /**

      * Set max selector pool size.

      * @param size max pool size

      */

     public final static void setMaxSelectors(int size) throws IOException {

         synchronized(selectors) {

             if (size > maxSelectors || !initialized) {

                 // if not initialized yet - grow cache by size

                 if (!initialized) maxSelectors = 0;

                 grow(size);

             }  else if (size < maxSelectors) {

                 reduce(size);

             }

             maxSelectors = size;

             initialized = true;

         }

     }

     /**

      * Returns max selector pool size

      * @return max pool size

      */

     public final static int getMaxSelectors() {

         return maxSelectors;

     }

     /**

      * Get a exclusive {@link Selector}

      * @return {@link Selector}

      */

     public final static Selector getSelector() {

         synchronized(selectors) {

             if (!initialized) {

                 try {

                     setMaxSelectors(maxSelectors);

                 } catch (IOException e) {

                     Logger logger = Controller.logger();

                     if (logger.isLoggable(Level.WARNING)) {

                         logger.log(Level.WARNING, "SelectorFactory lazy initialization", e);

                     }

                 }

             }

             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 {@link Selector} to the cache

      * @param s {@link Selector}

      */

     public final static void returnSelector(Selector s) {

         synchronized(selectors) {

             selectors.push(s);

             if (selectors.size() == 1)

                 selectors.notify();

         }

     }

     /**

      * Executes <code>Selector.selectNow()</code> and returns 

      * the {@link Selector} to the cache

      */

     public final static void selectNowAndReturnSelector(Selector s) {

         try {

             s.selectNow();

             returnSelector(s);

         } catch(IOException e) {

             Logger logger = Controller.logger();

             logger.log(Level.WARNING, 

                     "Unexpected problem when releasing temporary Selector", e);

             try {

                 s.close();

             } catch(IOException ee) {

                 // We are not interested

             }

             try {

                 reimburseSelector();

             } catch(IOException ee) {

                 logger.log(Level.WARNING,

                         "Problematic Selector could not be reimbursed!", ee);

             }

         }

     }

     /**

      * Add Selector to the cache.

      * This method could be called to reimberse a lost or problematic Selector.

      * 

      * @throws java.io.IOException

      */

     public final static void reimburseSelector() throws IOException {

         returnSelector(createSelector());

     }

     /**

      * Creeate Selector

      * @return Selector

      * @throws java.io.IOException

      */

     protected static Selector createSelector() throws IOException {

         return Selector.open();

     }

     /**

      * Increase {@link Selector} pool size

      */

     private static void grow(int size) throws IOException {

         for(int i=0; i<size - maxSelectors; i++) {

             selectors.add(createSelector());

         }

     }

     /**

      * Decrease {@link Selector} 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 logger = Controller.logger();

                 if (logger.isLoggable(Level.FINE)) {

                     logger.log(Level.FINE, "SelectorFactory.reduce", e);

                 }

             }

         }

     }

 }