/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package org.jboss.netty.channel.socket.nio;
  
  import java.nio.channels.Selector;
  import java.util.concurrent.Executor;
  import java.util.concurrent.Executors;
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.ThreadPoolExecutor;
  
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelPipeline;
  import org.jboss.netty.channel.group.ChannelGroup;
  import org.jboss.netty.channel.socket.ServerSocketChannel;
  import org.jboss.netty.channel.socket.ServerSocketChannelFactory;
  import org.jboss.netty.util.ExternalResourceReleasable;
  
  /**
   * A {@link ServerSocketChannelFactory} which creates a server-side NIO-based
   * {@link ServerSocketChannel}.  It utilizes the non-blocking I/O mode which
   * was introduced with NIO to serve many number of concurrent connections
   * efficiently.
   *
   * <h3>How threads work</h3>
   * <p>
   * There are two types of threads in a {@link NioServerSocketChannelFactory};
   * one is boss thread and the other is worker thread.
   *
   * <h4>Boss threads</h4>
   * <p>
   * Each bound {@link ServerSocketChannel} has its own boss thread.
   * For example, if you opened two server ports such as 80 and 443, you will
   * have two boss threads.  A boss thread accepts incoming connections until
   * the port is unbound.  Once a connection is accepted successfully, the boss
   * thread passes the accepted {@link Channel} to one of the worker
   * threads that the {@link NioServerSocketChannelFactory} manages.
   *
   * <h4>Worker threads</h4>
   * <p>
   * One {@link NioServerSocketChannelFactory} can have one or more worker
   * threads.  A worker thread performs non-blocking read and write for one or
   * more {@link Channel}s in a non-blocking mode.
   *
   * <h3>Life cycle of threads and graceful shutdown</h3>
   * <p>
   * All threads are acquired from the {@link Executor}s which were specified
   * when a {@link NioServerSocketChannelFactory} was created.  Boss threads are
   * acquired from the {@code bossExecutor}, and worker threads are acquired from
   * the {@code workerExecutor}.  Therefore, you should make sure the specified
   * {@link Executor}s are able to lend the sufficient number of threads.
   * It is the best bet to specify {@linkplain Executors#newCachedThreadPool() a cached thread pool}.
   * <p>
   * Both boss and worker threads are acquired lazily, and then released when
   * there's nothing left to process.  All the related resources such as
   * {@link Selector} are also released when the boss and worker threads are
   * released.  Therefore, to shut down a service gracefully, you should do the
   * following:
   *
   * <ol>
   * <li>unbind all channels created by the factory,
   * <li>close all child channels accepted by the unbound channels, and
   *     (these two steps so far is usually done using {@link ChannelGroup#close()})</li>
   * <li>call {@link #releaseExternalResources()}.</li>
   * </ol>
   *
   * Please make sure not to shut down the executor until all channels are
   * closed.  Otherwise, you will end up with a {@link RejectedExecutionException}
   * and the related resources might not be released properly.
   *
   * @apiviz.landmark
   */
  public class NioServerSocketChannelFactory implements ServerSocketChannelFactory {
  
      private final WorkerPool<NioWorker> workerPool;
      private final NioServerSocketPipelineSink sink;
      private final BossPool<NioServerBoss> bossPool;
      private boolean releasePools;
  
      /**
       * Create a new {@link NioServerSocketChannelFactory} using {@link Executors#newCachedThreadPool()}
       * for the boss and worker.
       *
       * See {@link #NioServerSocketChannelFactory(Executor, Executor)}
       */
      public NioServerSocketChannelFactory() {
          this(Executors.newCachedThreadPool(), Executors.newCachedThreadPool());
         releasePools = true;
     }
 
     /**
      * Creates a new instance.  Calling this constructor is same with calling
      * {@link #NioServerSocketChannelFactory(Executor, Executor, int)} with
      * the worker executor passed into {@link #getMaxThreads(Executor)}.
      *
      * @param bossExecutor
      *        the {@link Executor} which will execute the boss threads
      * @param workerExecutor
      *        the {@link Executor} which will execute the I/O worker threads
      */
     public NioServerSocketChannelFactory(
             Executor bossExecutor, Executor workerExecutor) {
         this(bossExecutor, workerExecutor, getMaxThreads(workerExecutor));
     }
 
     /**
      * Creates a new instance.
      *
      * @param bossExecutor
      *        the {@link Executor} which will execute the boss threads
      * @param workerExecutor
      *        the {@link Executor} which will execute the I/O worker threads
      * @param workerCount
      *        the maximum number of I/O worker threads
      */
     public NioServerSocketChannelFactory(
             Executor bossExecutor, Executor workerExecutor,
             int workerCount) {
         this(bossExecutor, 1, workerExecutor, workerCount);
     }
 
     /**
      * Create a new instance.
      *
      * @param bossExecutor
      *        the {@link Executor} which will execute the boss threads
      * @param bossCount
      *        the number of boss threads
      * @param workerExecutor
      *        the {@link Executor} which will execute the I/O worker threads
      * @param workerCount
      *        the maximum number of I/O worker threads
      */
     public NioServerSocketChannelFactory(
             Executor bossExecutor, int bossCount, Executor workerExecutor,
             int workerCount) {
         this(bossExecutor, bossCount, new NioWorkerPool(workerExecutor, workerCount));
     }
 
     /**
      * Creates a new instance.
      *
      * @param bossExecutor
      *        the {@link Executor} which will execute the boss threads
      * @param workerPool
      *        the {@link WorkerPool} which will be used to obtain the {@link NioWorker} that execute
      *        the I/O worker threads
      */
     public NioServerSocketChannelFactory(
             Executor bossExecutor, WorkerPool<NioWorker> workerPool) {
         this(bossExecutor, 1 , workerPool);
     }
 
     /**
      * Create a new instance.
      *
      * @param bossExecutor
      *        the {@link Executor} which will execute the boss threads
      * @param bossCount
      *        the number of boss threads
      * @param workerPool
      *        the {@link WorkerPool} which will be used to obtain the {@link NioWorker} that execute
      *        the I/O worker threads
      */
     public NioServerSocketChannelFactory(
             Executor bossExecutor, int bossCount, WorkerPool<NioWorker> workerPool) {
         this(new NioServerBossPool(bossExecutor, bossCount, null), workerPool);
     }
 
     /**
      * Create a new instance.
      *
      * @param bossPool
      *        the {@link BossPool} which will be used to obtain the {@link NioServerBoss} that execute
      *        the I/O for accept new connections
      * @param workerPool
      *        the {@link WorkerPool} which will be used to obtain the {@link NioWorker} that execute
      *        the I/O worker threads
      */
     public NioServerSocketChannelFactory(BossPool<NioServerBoss> bossPool, WorkerPool<NioWorker> workerPool) {
         if (bossPool == null) {
             throw new NullPointerException("bossExecutor");
         }
         if (workerPool == null) {
             throw new NullPointerException("workerPool");
         }
         this.bossPool = bossPool;
         this.workerPool = workerPool;
         sink = new NioServerSocketPipelineSink();
     }
 
     public ServerSocketChannel newChannel(ChannelPipeline pipeline) {
         return new NioServerSocketChannel(this, pipeline, sink, bossPool.nextBoss(), workerPool);
     }
 
     public void shutdown() {
         bossPool.shutdown();
         workerPool.shutdown();
         if (releasePools) {
             releasePools();
         }
     }
 
     public void releaseExternalResources() {
         bossPool.shutdown();
         workerPool.shutdown();
         releasePools();
     }
 
     private void releasePools() {
         if (bossPool instanceof ExternalResourceReleasable) {
             ((ExternalResourceReleasable) bossPool).releaseExternalResources();
         }
         if (workerPool instanceof ExternalResourceReleasable) {
             ((ExternalResourceReleasable) workerPool).releaseExternalResources();
         }
     }
 
     /**
      * Returns number of max threads for the {@link NioWorkerPool} to use. If
      * the * {@link Executor} is a {@link ThreadPoolExecutor}, check its
      * maximum * pool size and return either it's maximum or
      * {@link SelectorUtil#DEFAULT_IO_THREADS}, whichever is lower. Note that
      * {@link SelectorUtil#DEFAULT_IO_THREADS} is 2 * the number of available
      * processors in the machine.  The number of available processors is
      * obtained by {@link Runtime#availableProcessors()}.
      *
      * @param executor
      *        the {@link Executor} which will execute the I/O worker threads
      * @return
      *        number of maximum threads the NioWorkerPool should use
      */
     private static int getMaxThreads(Executor executor) {
         if (executor instanceof ThreadPoolExecutor) {
             final int maxThreads = ((ThreadPoolExecutor) executor).getMaximumPoolSize();
             return Math.min(maxThreads, SelectorUtil.DEFAULT_IO_THREADS);
         }
         return SelectorUtil.DEFAULT_IO_THREADS;
     }
 }