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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.handler.timeout;
  
  import io.netty.bootstrap.ServerBootstrap;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInitializer;
  import io.netty.channel.ChannelOutboundHandlerAdapter;
  import io.netty.channel.ChannelPromise;
  
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.TimeUnit;
  
  /**
   * Raises a {@link WriteTimeoutException} when a write operation cannot finish in a certain period of time.
   *
   * <pre>
   * // The connection is closed when a write operation cannot finish in 30 seconds.
   *
   * public class MyChannelInitializer extends {@link ChannelInitializer}&lt;{@link Channel}&gt; {
   *     public void initChannel({@link Channel} channel) {
   *         channel.pipeline().addLast("writeTimeoutHandler", new {@link WriteTimeoutHandler}(30);
   *         channel.pipeline().addLast("myHandler", new MyHandler());
   *     }
   * }
   *
   * // Handler should handle the {@link WriteTimeoutException}.
   * public class MyHandler extends {@link ChannelDuplexHandler} {
   *     {@code @Override}
   *     public void exceptionCaught({@link ChannelHandlerContext} ctx, {@link Throwable} cause)
   *             throws {@link Exception} {
   *         if (cause instanceof {@link WriteTimeoutException}) {
   *             // do something
   *         } else {
   *             super.exceptionCaught(ctx, cause);
   *         }
   *     }
   * }
   *
   * {@link ServerBootstrap} bootstrap = ...;
   * ...
   * bootstrap.childHandler(new MyChannelInitializer());
   * ...
   * </pre>
   * @see ReadTimeoutHandler
   * @see IdleStateHandler
   */
  public class WriteTimeoutHandler extends ChannelOutboundHandlerAdapter {
      private static final long MIN_TIMEOUT_NANOS = TimeUnit.MILLISECONDS.toNanos(1);
  
      private final long timeoutNanos;
  
      /**
       * A doubly-linked list to track all WriteTimeoutTasks
       */
      private WriteTimeoutTask lastTask;
  
      private boolean closed;
  
      /**
       * Creates a new instance.
       *
       * @param timeoutSeconds
       *        write timeout in seconds
       */
      public WriteTimeoutHandler(int timeoutSeconds) {
          this(timeoutSeconds, TimeUnit.SECONDS);
      }
  
      /**
       * Creates a new instance.
       *
       * @param timeout
       *        write timeout
       * @param unit
       *        the {@link TimeUnit} of {@code timeout}
       */
      public WriteTimeoutHandler(long timeout, TimeUnit unit) {
          if (unit == null) {
              throw new NullPointerException("unit");
          }
  
         if (timeout <= 0) {
             timeoutNanos = 0;
         } else {
             timeoutNanos = Math.max(unit.toNanos(timeout), MIN_TIMEOUT_NANOS);
         }
     }
 
     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
         scheduleTimeout(ctx, promise);
         ctx.write(msg, promise);
     }
 
     @Override
     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
         WriteTimeoutTask task = lastTask;
         lastTask = null;
         while (task != null) {
             task.scheduledFuture.cancel(false);
             WriteTimeoutTask prev = task.prev;
             task.prev = null;
             task.next = null;
             task = prev;
         }
     }
 
     private void scheduleTimeout(final ChannelHandlerContext ctx, final ChannelPromise promise) {
         // Schedule a timeout.
         final WriteTimeoutTask task = new WriteTimeoutTask(ctx, promise);
         task.scheduledFuture = ctx.executor().schedule(task, timeoutNanos, TimeUnit.NANOSECONDS);
 
         if (!task.scheduledFuture.isDone()) {
             addWriteTimeoutTask(task);
 
             // Cancel the scheduled timeout if the flush promise is complete.
             promise.addListener(task);
         }
     }
 
     private void addWriteTimeoutTask(WriteTimeoutTask task) {
         if (lastTask == null) {
             lastTask = task;
         } else {
             lastTask.next = task;
             task.prev = lastTask;
             lastTask = task;
         }
     }
 
     private void removeWriteTimeoutTask(WriteTimeoutTask task) {
         if (task == lastTask) {
             // task is the tail of list
             assert task.next == null;
             lastTask = lastTask.prev;
             if (lastTask != null) {
                 lastTask.next = null;
             }
         } else if (task.prev == null && task.next == null) {
             // Since task is not lastTask, then it has been removed or not been added.
             return;
         } else if (task.prev == null) {
             // task is the head of list and the list has at least 2 nodes
             task.next.prev = null;
         } else {
             task.prev.next = task.next;
             task.next.prev = task.prev;
         }
         task.prev = null;
         task.next = null;
     }
 
     /**
      * Is called when a write timeout was detected
      */
     protected void writeTimedOut(ChannelHandlerContext ctx) throws Exception {
         if (!closed) {
             ctx.fireExceptionCaught(WriteTimeoutException.INSTANCE);
             ctx.close();
             closed = true;
         }
     }
 
     private final class WriteTimeoutTask implements Runnable, ChannelFutureListener {
 
         private final ChannelHandlerContext ctx;
         private final ChannelPromise promise;
 
         // WriteTimeoutTask is also a node of a doubly-linked list
         WriteTimeoutTask prev;
         WriteTimeoutTask next;
 
         ScheduledFuture<?> scheduledFuture;
 
         WriteTimeoutTask(ChannelHandlerContext ctx, ChannelPromise promise) {
             this.ctx = ctx;
             this.promise = promise;
         }
 
         @Override
         public void run() {
             // Was not written yet so issue a write timeout
             // The promise itself will be failed with a ClosedChannelException once the close() was issued
             // See https://github.com/netty/netty/issues/2159
             if (!promise.isDone()) {
                 try {
                     writeTimedOut(ctx);
                 } catch (Throwable t) {
                     ctx.fireExceptionCaught(t);
                 }
             }
             removeWriteTimeoutTask(this);
         }
 
         @Override
         public void operationComplete(ChannelFuture future) throws Exception {
             // scheduledFuture has already be set when reaching here
             scheduledFuture.cancel(false);
             removeWriteTimeoutTask(this);
         }
     }
 }