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   /*
    * 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 io.netty.channel;
  
  
  import io.netty.util.concurrent.AbstractEventExecutorGroup;
  import io.netty.util.concurrent.DefaultPromise;
  import io.netty.util.concurrent.EventExecutor;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.FutureListener;
  import io.netty.util.concurrent.GlobalEventExecutor;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.internal.EmptyArrays;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.ReadOnlyIterator;
  import io.netty.util.internal.ThrowableUtil;
  
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.Queue;
  import java.util.Set;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.Executors;
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.TimeUnit;
  
  /**
   * An {@link EventLoopGroup} that creates one {@link EventLoop} per {@link Channel}.
   */
  public class ThreadPerChannelEventLoopGroup extends AbstractEventExecutorGroup implements EventLoopGroup {
  
      private final Object[] childArgs;
      private final int maxChannels;
      final ThreadFactory threadFactory;
      final Set<ThreadPerChannelEventLoop> activeChildren =
              Collections.newSetFromMap(PlatformDependent.<ThreadPerChannelEventLoop, Boolean>newConcurrentHashMap());
      final Queue<ThreadPerChannelEventLoop> idleChildren = new ConcurrentLinkedQueue<ThreadPerChannelEventLoop>();
      private final ChannelException tooManyChannels;
  
      private volatile boolean shuttingDown;
      private final Promise<?> terminationFuture = new DefaultPromise<Void>(GlobalEventExecutor.INSTANCE);
      private final FutureListener<Object> childTerminationListener = new FutureListener<Object>() {
          @Override
          public void operationComplete(Future<Object> future) throws Exception {
              // Inefficient, but works.
              if (isTerminated()) {
                  terminationFuture.trySuccess(null);
              }
          }
      };
  
      /**
       * Create a new {@link ThreadPerChannelEventLoopGroup} with no limit in place.
       */
      protected ThreadPerChannelEventLoopGroup() {
          this(0);
      }
  
      /**
       * Create a new {@link ThreadPerChannelEventLoopGroup}.
       *
       * @param maxChannels       the maximum number of channels to handle with this instance. Once you try to register
       *                          a new {@link Channel} and the maximum is exceed it will throw an
       *                          {@link ChannelException} on the {@link #register(Channel)} and
       *                          {@link #register(Channel, ChannelPromise)} method.
       *                          Use {@code 0} to use no limit
       */
      protected ThreadPerChannelEventLoopGroup(int maxChannels) {
          this(maxChannels, Executors.defaultThreadFactory());
      }
  
      /**
       * Create a new {@link ThreadPerChannelEventLoopGroup}.
       *
       * @param maxChannels       the maximum number of channels to handle with this instance. Once you try to register
       *                          a new {@link Channel} and the maximum is exceed it will throw an
       *                          {@link ChannelException} on the {@link #register(Channel)} and
       *                          {@link #register(Channel, ChannelPromise)} method.
       *                          Use {@code 0} to use no limit
       * @param threadFactory     the {@link ThreadFactory} used to create new {@link Thread} instances that handle the
       *                          registered {@link Channel}s
       * @param args              arguments which will passed to each {@link #newChild(Object...)} call.
       */
      protected ThreadPerChannelEventLoopGroup(int maxChannels, ThreadFactory threadFactory, Object... args) {
          if (maxChannels < 0) {
             throw new IllegalArgumentException(String.format(
                     "maxChannels: %d (expected: >= 0)", maxChannels));
         }
         if (threadFactory == null) {
             throw new NullPointerException("threadFactory");
         }
 
         if (args == null) {
             childArgs = EmptyArrays.EMPTY_OBJECTS;
         } else {
             childArgs = args.clone();
         }
 
         this.maxChannels = maxChannels;
         this.threadFactory = threadFactory;
 
         tooManyChannels = ThrowableUtil.unknownStackTrace(
                 new ChannelException("too many channels (max: " + maxChannels + ')'),
                 ThreadPerChannelEventLoopGroup.class, "nextChild()");
     }
 
     /**
      * Creates a new {@link EventLoop}.  The default implementation creates a new {@link ThreadPerChannelEventLoop}.
      */
     protected ThreadPerChannelEventLoop newChild(
             @SuppressWarnings("UnusedParameters") Object... args) throws Exception {
         return new ThreadPerChannelEventLoop(this);
     }
 
     @Override
     public Iterator<EventExecutor> iterator() {
         return new ReadOnlyIterator<EventExecutor>(activeChildren.iterator());
     }
 
     @Override
     public EventLoop next() {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
         shuttingDown = true;
 
         for (EventLoop l: activeChildren) {
             l.shutdownGracefully(quietPeriod, timeout, unit);
         }
         for (EventLoop l: idleChildren) {
             l.shutdownGracefully(quietPeriod, timeout, unit);
         }
 
         // Notify the future if there was no children.
         if (isTerminated()) {
             terminationFuture.trySuccess(null);
         }
 
         return terminationFuture();
     }
 
     @Override
     public Future<?> terminationFuture() {
         return terminationFuture;
     }
 
     @Override
     @Deprecated
     public void shutdown() {
         shuttingDown = true;
 
         for (EventLoop l: activeChildren) {
             l.shutdown();
         }
         for (EventLoop l: idleChildren) {
             l.shutdown();
         }
 
         // Notify the future if there was no children.
         if (isTerminated()) {
             terminationFuture.trySuccess(null);
         }
     }
 
     @Override
     public boolean isShuttingDown() {
         for (EventLoop l: activeChildren) {
             if (!l.isShuttingDown()) {
                 return false;
             }
         }
         for (EventLoop l: idleChildren) {
             if (!l.isShuttingDown()) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     public boolean isShutdown() {
         for (EventLoop l: activeChildren) {
             if (!l.isShutdown()) {
                 return false;
             }
         }
         for (EventLoop l: idleChildren) {
             if (!l.isShutdown()) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     public boolean isTerminated() {
         for (EventLoop l: activeChildren) {
             if (!l.isTerminated()) {
                 return false;
             }
         }
         for (EventLoop l: idleChildren) {
             if (!l.isTerminated()) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     public boolean awaitTermination(long timeout, TimeUnit unit)
             throws InterruptedException {
         long deadline = System.nanoTime() + unit.toNanos(timeout);
         for (EventLoop l: activeChildren) {
             for (;;) {
                 long timeLeft = deadline - System.nanoTime();
                 if (timeLeft <= 0) {
                     return isTerminated();
                 }
                 if (l.awaitTermination(timeLeft, TimeUnit.NANOSECONDS)) {
                     break;
                 }
             }
         }
         for (EventLoop l: idleChildren) {
             for (;;) {
                 long timeLeft = deadline - System.nanoTime();
                 if (timeLeft <= 0) {
                     return isTerminated();
                 }
                 if (l.awaitTermination(timeLeft, TimeUnit.NANOSECONDS)) {
                     break;
                 }
             }
         }
         return isTerminated();
     }
 
     @Override
     public ChannelFuture register(Channel channel) {
         if (channel == null) {
             throw new NullPointerException("channel");
         }
         try {
             EventLoop l = nextChild();
             return l.register(channel, new DefaultChannelPromise(channel, l));
         } catch (Throwable t) {
             return new FailedChannelFuture(channel, GlobalEventExecutor.INSTANCE, t);
         }
     }
 
     @Override
     public ChannelFuture register(Channel channel, ChannelPromise promise) {
         if (channel == null) {
             throw new NullPointerException("channel");
         }
         try {
             return nextChild().register(channel, promise);
         } catch (Throwable t) {
             promise.setFailure(t);
             return promise;
         }
     }
 
     private EventLoop nextChild() throws Exception {
         if (shuttingDown) {
             throw new RejectedExecutionException("shutting down");
         }
 
         ThreadPerChannelEventLoop loop = idleChildren.poll();
         if (loop == null) {
             if (maxChannels > 0 && activeChildren.size() >= maxChannels) {
                 throw tooManyChannels;
             }
             loop = newChild(childArgs);
             loop.terminationFuture().addListener(childTerminationListener);
         }
         activeChildren.add(loop);
         return loop;
     }
 }