/*
    * 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:
    *
    *   https://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.embedded;
  
  import io.netty.channel.AbstractChannel;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelConfig;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelId;
  import io.netty.channel.ChannelInitializer;
  import io.netty.channel.ChannelMetadata;
  import io.netty.channel.ChannelOutboundBuffer;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.DefaultChannelConfig;
  import io.netty.channel.DefaultChannelPipeline;
  import io.netty.channel.EventLoop;
  import io.netty.channel.RecvByteBufAllocator;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.concurrent.Ticker;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.RecyclableArrayList;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.net.SocketAddress;
  import java.nio.channels.ClosedChannelException;
  import java.util.ArrayDeque;
  import java.util.Objects;
  import java.util.Queue;
  import java.util.concurrent.TimeUnit;
  
  /**
   * Base class for {@link Channel} implementations that are used in an embedded fashion.
   */
  public class EmbeddedChannel extends AbstractChannel {
  
      private static final SocketAddress LOCAL_ADDRESS = new EmbeddedSocketAddress();
      private static final SocketAddress REMOTE_ADDRESS = new EmbeddedSocketAddress();
  
      private static final ChannelHandler[] EMPTY_HANDLERS = new ChannelHandler[0];
      private enum State { OPEN, ACTIVE, CLOSED }
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(EmbeddedChannel.class);
  
      private static final ChannelMetadata METADATA_NO_DISCONNECT = new ChannelMetadata(false);
      private static final ChannelMetadata METADATA_DISCONNECT = new ChannelMetadata(true);
  
      private final EmbeddedEventLoop loop;
      private final ChannelFutureListener recordExceptionListener = new ChannelFutureListener() {
          @Override
          public void operationComplete(ChannelFuture future) throws Exception {
              recordException(future);
          }
      };
  
      private final ChannelMetadata metadata;
      private final ChannelConfig config;
  
      private Queue<Object> inboundMessages;
      private Queue<Object> outboundMessages;
      private Throwable lastException;
      private State state;
      private int executingStackCnt;
      private boolean cancelRemainingScheduledTasks;
  
      /**
       * Create a new instance with an {@link EmbeddedChannelId} and an empty pipeline.
       */
      public EmbeddedChannel() {
          this(builder());
      }
  
      /**
       * Create a new instance with the specified ID and an empty pipeline.
       *
       * @param channelId the {@link ChannelId} that will be used to identify this channel
       */
      public EmbeddedChannel(ChannelId channelId) {
          this(builder().channelId(channelId));
      }
  
      /**
      * Create a new instance with the pipeline initialized with the specified handlers.
      *
      * @param handlers the {@link ChannelHandler}s which will be add in the {@link ChannelPipeline}
      */
     public EmbeddedChannel(ChannelHandler... handlers) {
         this(builder().handlers(handlers));
     }
 
     /**
      * Create a new instance with the pipeline initialized with the specified handlers.
      *
      * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()}
      *                      to {@link #close()}, {@code true} otherwise.
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(boolean hasDisconnect, ChannelHandler... handlers) {
         this(builder().hasDisconnect(hasDisconnect).handlers(handlers));
     }
 
     /**
      * Create a new instance with the pipeline initialized with the specified handlers.
      *
      * @param register {@code true} if this {@link Channel} is registered to the {@link EventLoop} in the
      *                 constructor. If {@code false} the user will need to call {@link #register()}.
      * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()}
      *                      to {@link #close()}, {@code true} otherwise.
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(boolean register, boolean hasDisconnect, ChannelHandler... handlers) {
         this(builder().register(register).hasDisconnect(hasDisconnect).handlers(handlers));
     }
 
     /**
      * Create a new instance with the channel ID set to the given ID and the pipeline
      * initialized with the specified handlers.
      *
      * @param channelId the {@link ChannelId} that will be used to identify this channel
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(ChannelId channelId, ChannelHandler... handlers) {
         this(builder().channelId(channelId).handlers(handlers));
     }
 
     /**
      * Create a new instance with the channel ID set to the given ID and the pipeline
      * initialized with the specified handlers.
      *
      * @param channelId the {@link ChannelId} that will be used to identify this channel
      * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()}
      *                      to {@link #close()}, {@code true} otherwise.
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(ChannelId channelId, boolean hasDisconnect, ChannelHandler... handlers) {
         this(builder().channelId(channelId).hasDisconnect(hasDisconnect).handlers(handlers));
     }
 
     /**
      * Create a new instance with the channel ID set to the given ID and the pipeline
      * initialized with the specified handlers.
      *
      * @param channelId the {@link ChannelId} that will be used to identify this channel
      * @param register {@code true} if this {@link Channel} is registered to the {@link EventLoop} in the
      *                 constructor. If {@code false} the user will need to call {@link #register()}.
      * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()}
      *                      to {@link #close()}, {@code true} otherwise.
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(ChannelId channelId, boolean register, boolean hasDisconnect,
                            ChannelHandler... handlers) {
         this(builder().channelId(channelId).register(register).hasDisconnect(hasDisconnect).handlers(handlers));
     }
 
     /**
      * Create a new instance with the channel ID set to the given ID and the pipeline
      * initialized with the specified handlers.
      *
      * @param parent    the parent {@link Channel} of this {@link EmbeddedChannel}.
      * @param channelId the {@link ChannelId} that will be used to identify this channel
      * @param register {@code true} if this {@link Channel} is registered to the {@link EventLoop} in the
      *                 constructor. If {@code false} the user will need to call {@link #register()}.
      * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()}
      *                      to {@link #close()}, {@code true} otherwise.
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(Channel parent, ChannelId channelId, boolean register, boolean hasDisconnect,
                            final ChannelHandler... handlers) {
         this(builder()
                 .parent(parent)
                 .channelId(channelId)
                 .register(register)
                 .hasDisconnect(hasDisconnect)
                 .handlers(handlers));
     }
 
     /**
      * Create a new instance with the channel ID set to the given ID and the pipeline
      * initialized with the specified handlers.
      *
      * @param channelId the {@link ChannelId} that will be used to identify this channel
      * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()}
      *                      to {@link #close()}, {@code true} otherwise.
      * @param config the {@link ChannelConfig} which will be returned by {@link #config()}.
      * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
      */
     public EmbeddedChannel(ChannelId channelId, boolean hasDisconnect, final ChannelConfig config,
                            final ChannelHandler... handlers) {
         this(builder().channelId(channelId).hasDisconnect(hasDisconnect).config(config).handlers(handlers));
     }
 
     /**
      * Create a new instance with the configuration from the given builder. This method is {@code protected} for use by
      * subclasses; Otherwise, please use {@link Builder#build()}.
      *
      * @param builder The builder
      */
     protected EmbeddedChannel(Builder builder) {
         super(builder.parent, builder.channelId);
         loop = new EmbeddedEventLoop(builder.ticker == null ? new EmbeddedEventLoop.FreezableTicker() : builder.ticker);
         metadata = metadata(builder.hasDisconnect);
         config = builder.config == null ? new DefaultChannelConfig(this) : builder.config;
         if (builder.handler == null) {
             setup(builder.register, builder.handlers);
         } else {
             setup(builder.register, builder.handler);
         }
     }
 
     private static ChannelMetadata metadata(boolean hasDisconnect) {
         return hasDisconnect ? METADATA_DISCONNECT : METADATA_NO_DISCONNECT;
     }
 
     private void setup(boolean register, final ChannelHandler... handlers) {
         ChannelPipeline p = pipeline();
         p.addLast(new ChannelInitializer<Channel>() {
             @Override
             protected void initChannel(Channel ch) {
                 ChannelPipeline pipeline = ch.pipeline();
                 for (ChannelHandler h: handlers) {
                     if (h == null) {
                         break;
                     }
                     pipeline.addLast(h);
                 }
             }
         });
         if (register) {
             ChannelFuture future = loop.register(this);
             assert future.isDone();
         }
     }
 
     private void setup(boolean register, final ChannelHandler handler) {
         ChannelPipeline p = pipeline();
         p.addLast(handler);
         if (register) {
             ChannelFuture future = loop.register(this);
             assert future.isDone();
         }
     }
 
     /**
      * Register this {@code Channel} on its {@link EventLoop}.
      */
     public void register() throws Exception {
         ChannelFuture future = loop.register(this);
         assert future.isDone();
         Throwable cause = future.cause();
         if (cause != null) {
             PlatformDependent.throwException(cause);
         }
     }
 
     @Override
     protected final DefaultChannelPipeline newChannelPipeline() {
         return new EmbeddedChannelPipeline(this);
     }
 
     @Override
     public ChannelMetadata metadata() {
         return metadata;
     }
 
     @Override
     public ChannelConfig config() {
         return config;
     }
 
     @Override
     public boolean isOpen() {
         return state != State.CLOSED;
     }
 
     @Override
     public boolean isActive() {
         return state == State.ACTIVE;
     }
 
     /**
      * Returns the {@link Queue} which holds all the {@link Object}s that were received by this {@link Channel}.
      */
     public Queue<Object> inboundMessages() {
         if (inboundMessages == null) {
             inboundMessages = new ArrayDeque<Object>();
         }
         return inboundMessages;
     }
 
     /**
      * @deprecated use {@link #inboundMessages()}
      */
     @Deprecated
     public Queue<Object> lastInboundBuffer() {
         return inboundMessages();
     }
 
     /**
      * Returns the {@link Queue} which holds all the {@link Object}s that were written by this {@link Channel}.
      */
     public Queue<Object> outboundMessages() {
         if (outboundMessages == null) {
             outboundMessages = new ArrayDeque<Object>();
         }
         return outboundMessages;
     }
 
     /**
      * @deprecated use {@link #outboundMessages()}
      */
     @Deprecated
     public Queue<Object> lastOutboundBuffer() {
         return outboundMessages();
     }
 
     /**
      * Return received data from this {@link Channel}
      */
     @SuppressWarnings("unchecked")
     public <T> T readInbound() {
         T message = (T) poll(inboundMessages);
         if (message != null) {
             ReferenceCountUtil.touch(message, "Caller of readInbound() will handle the message from this point");
         }
         return message;
     }
 
     /**
      * Read data from the outbound. This may return {@code null} if nothing is readable.
      */
     @SuppressWarnings("unchecked")
     public <T> T readOutbound() {
         T message =  (T) poll(outboundMessages);
         if (message != null) {
             ReferenceCountUtil.touch(message, "Caller of readOutbound() will handle the message from this point.");
         }
         return message;
     }
 
     /**
      * Write messages to the inbound of this {@link Channel}.
      *
      * @param msgs the messages to be written
      *
      * @return {@code true} if the write operation did add something to the inbound buffer
      */
     public boolean writeInbound(Object... msgs) {
         ensureOpen();
         if (msgs.length == 0) {
             return isNotEmpty(inboundMessages);
         }
 
         executingStackCnt++;
         try {
             ChannelPipeline p = pipeline();
             for (Object m : msgs) {
                 p.fireChannelRead(m);
             }
 
             flushInbound(false, voidPromise());
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
         return isNotEmpty(inboundMessages);
     }
 
     /**
      * Writes one message to the inbound of this {@link Channel} and does not flush it. This
      * method is conceptually equivalent to {@link #write(Object)}.
      *
      * @see #writeOneOutbound(Object)
      */
     public ChannelFuture writeOneInbound(Object msg) {
         return writeOneInbound(msg, newPromise());
     }
 
     /**
      * Writes one message to the inbound of this {@link Channel} and does not flush it. This
      * method is conceptually equivalent to {@link #write(Object, ChannelPromise)}.
      *
      * @see #writeOneOutbound(Object, ChannelPromise)
      */
     public ChannelFuture writeOneInbound(Object msg, ChannelPromise promise) {
         executingStackCnt++;
         try {
             if (checkOpen(true)) {
                 pipeline().fireChannelRead(msg);
             }
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
         return checkException(promise);
     }
 
     /**
      * Flushes the inbound of this {@link Channel}. This method is conceptually equivalent to {@link #flush()}.
      *
      * @see #flushOutbound()
      */
     public EmbeddedChannel flushInbound() {
         flushInbound(true, voidPromise());
         return this;
     }
 
     private ChannelFuture flushInbound(boolean recordException, ChannelPromise promise) {
         executingStackCnt++;
         try {
             if (checkOpen(recordException)) {
                 pipeline().fireChannelReadComplete();
                 runPendingTasks();
             }
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
 
       return checkException(promise);
     }
 
     /**
      * Write messages to the outbound of this {@link Channel}.
      *
      * @param msgs              the messages to be written
      * @return bufferReadable   returns {@code true} if the write operation did add something to the outbound buffer
      */
     public boolean writeOutbound(Object... msgs) {
         ensureOpen();
         if (msgs.length == 0) {
             return isNotEmpty(outboundMessages);
         }
 
         executingStackCnt++;
         RecyclableArrayList futures = RecyclableArrayList.newInstance(msgs.length);
         try {
             try {
                 for (Object m : msgs) {
                     if (m == null) {
                         break;
                     }
                     futures.add(write(m));
                 }
 
                 flushOutbound0();
 
                 int size = futures.size();
                 for (int i = 0; i < size; i++) {
                     ChannelFuture future = (ChannelFuture) futures.get(i);
                     if (future.isDone()) {
                         recordException(future);
                     } else {
                         // The write may be delayed to run later by runPendingTasks()
                         future.addListener(recordExceptionListener);
                     }
                 }
             } finally {
                 executingStackCnt--;
                 maybeRunPendingTasks();
             }
             checkException();
             return isNotEmpty(outboundMessages);
         } finally {
             futures.recycle();
         }
     }
 
     /**
      * Writes one message to the outbound of this {@link Channel} and does not flush it. This
      * method is conceptually equivalent to {@link #write(Object)}.
      *
      * @see #writeOneInbound(Object)
      */
     public ChannelFuture writeOneOutbound(Object msg) {
         return writeOneOutbound(msg, newPromise());
     }
 
     /**
      * Writes one message to the outbound of this {@link Channel} and does not flush it. This
      * method is conceptually equivalent to {@link #write(Object, ChannelPromise)}.
      *
      * @see #writeOneInbound(Object, ChannelPromise)
      */
     public ChannelFuture writeOneOutbound(Object msg, ChannelPromise promise) {
         executingStackCnt++;
         try {
             if (checkOpen(true)) {
                 return write(msg, promise);
             }
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
 
         return checkException(promise);
     }
 
     /**
      * Flushes the outbound of this {@link Channel}. This method is conceptually equivalent to {@link #flush()}.
      *
      * @see #flushInbound()
      */
     public EmbeddedChannel flushOutbound() {
         executingStackCnt++;
         try {
             if (checkOpen(true)) {
                 flushOutbound0();
             }
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
         checkException(voidPromise());
         return this;
     }
 
     private void flushOutbound0() {
         // We need to call runPendingTasks first as a ChannelOutboundHandler may used eventloop.execute(...) to
         // delay the write on the next eventloop run.
         runPendingTasks();
 
         flush();
     }
 
     /**
      * Mark this {@link Channel} as finished. Any further try to write data to it will fail.
      *
      * @return bufferReadable returns {@code true} if any of the used buffers has something left to read
      */
     public boolean finish() {
         return finish(false);
     }
 
     /**
      * Mark this {@link Channel} as finished and release all pending message in the inbound and outbound buffer.
      * Any further try to write data to it will fail.
      *
      * @return bufferReadable returns {@code true} if any of the used buffers has something left to read
      */
     public boolean finishAndReleaseAll() {
         return finish(true);
     }
 
     /**
      * Mark this {@link Channel} as finished. Any further try to write data to it will fail.
      *
      * @param releaseAll if {@code true} all pending message in the inbound and outbound buffer are released.
      * @return bufferReadable returns {@code true} if any of the used buffers has something left to read
      */
     private boolean finish(boolean releaseAll) {
         executingStackCnt++;
         try {
             close();
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
         try {
             checkException();
             return isNotEmpty(inboundMessages) || isNotEmpty(outboundMessages);
         } finally {
             if (releaseAll) {
                 releaseAll(inboundMessages);
                 releaseAll(outboundMessages);
             }
         }
     }
 
     /**
      * Release all buffered inbound messages and return {@code true} if any were in the inbound buffer, {@code false}
      * otherwise.
      */
     public boolean releaseInbound() {
         return releaseAll(inboundMessages);
     }
 
     /**
      * Release all buffered outbound messages and return {@code true} if any were in the outbound buffer, {@code false}
      * otherwise.
      */
     public boolean releaseOutbound() {
         return releaseAll(outboundMessages);
     }
 
     private static boolean releaseAll(Queue<Object> queue) {
         if (isNotEmpty(queue)) {
             for (;;) {
                 Object msg = queue.poll();
                 if (msg == null) {
                     break;
                 }
                 ReferenceCountUtil.release(msg);
             }
             return true;
         }
         return false;
     }
 
     @Override
     public final ChannelFuture close() {
         return close(newPromise());
     }
 
     @Override
     public final ChannelFuture disconnect() {
         return disconnect(newPromise());
     }
 
     @Override
     public final ChannelFuture close(ChannelPromise promise) {
         // We need to call runPendingTasks() before calling super.close() as there may be something in the queue
         // that needs to be run before the actual close takes place.
         executingStackCnt++;
         ChannelFuture future;
         try {
             runPendingTasks();
             future = super.close(promise);
 
             cancelRemainingScheduledTasks = true;
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
         return future;
     }
 
     @Override
     public final ChannelFuture disconnect(ChannelPromise promise) {
         executingStackCnt++;
         ChannelFuture future;
         try {
             future = super.disconnect(promise);
 
             if (!metadata.hasDisconnect()) {
                 cancelRemainingScheduledTasks = true;
             }
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
         return future;
     }
 
     @Override
     public ChannelFuture bind(SocketAddress localAddress) {
         executingStackCnt++;
         try {
             return super.bind(localAddress);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture connect(SocketAddress remoteAddress) {
         executingStackCnt++;
         try {
             return super.connect(remoteAddress);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress) {
         executingStackCnt++;
         try {
             return super.connect(remoteAddress, localAddress);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture deregister() {
         executingStackCnt++;
         try {
             return super.deregister();
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public Channel flush() {
         executingStackCnt++;
         try {
             return super.flush();
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise) {
         executingStackCnt++;
         try {
             return super.bind(localAddress, promise);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise) {
         executingStackCnt++;
         try {
             return super.connect(remoteAddress, promise);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
         executingStackCnt++;
         try {
             return super.connect(remoteAddress, localAddress, promise);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture deregister(ChannelPromise promise) {
         executingStackCnt++;
         try {
             return super.deregister(promise);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public Channel read() {
         executingStackCnt++;
         try {
             return super.read();
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture write(Object msg) {
         executingStackCnt++;
         try {
             return super.write(msg);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture write(Object msg, ChannelPromise promise) {
         executingStackCnt++;
         try {
             return super.write(msg, promise);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture writeAndFlush(Object msg) {
         executingStackCnt++;
         try {
             return super.writeAndFlush(msg);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     @Override
     public ChannelFuture writeAndFlush(Object msg, ChannelPromise promise) {
         executingStackCnt++;
         try {
             return super.writeAndFlush(msg, promise);
         } finally {
             executingStackCnt--;
             maybeRunPendingTasks();
         }
     }
 
     private static boolean isNotEmpty(Queue<Object> queue) {
         return queue != null && !queue.isEmpty();
     }
 
     private static Object poll(Queue<Object> queue) {
         return queue != null ? queue.poll() : null;
     }
 
     private void maybeRunPendingTasks() {
         if (executingStackCnt == 0) {
             runPendingTasks();
 
             if (cancelRemainingScheduledTasks) {
                 // Cancel all scheduled tasks that are left.
                 embeddedEventLoop().cancelScheduledTasks();
             }
         }
     }
 
     /**
      * Run all tasks (which also includes scheduled tasks) that are pending in the {@link EventLoop}
      * for this {@link Channel}
      */
     public void runPendingTasks() {
         try {
             embeddedEventLoop().runTasks();
         } catch (Exception e) {
             recordException(e);
         }
 
         try {
             embeddedEventLoop().runScheduledTasks();
         } catch (Exception e) {
             recordException(e);
         }
     }
 
     /**
      * Check whether this channel has any pending tasks that would be executed by a call to {@link #runPendingTasks()}.
      * This includes normal tasks, and scheduled tasks where the deadline has expired. If this method returns
      * {@code false}, a call to {@link #runPendingTasks()} would do nothing.
      *
      * @return {@code true} if there are any pending tasks, {@code false} otherwise.
      */
     public boolean hasPendingTasks() {
         return embeddedEventLoop().hasPendingNormalTasks() ||
                 embeddedEventLoop().nextScheduledTask() == 0;
     }
 
     /**
      * Run all pending scheduled tasks in the {@link EventLoop} for this {@link Channel} and return the
      * {@code nanoseconds} when the next scheduled task is ready to run. If no other task was scheduled it will return
      * {@code -1}.
      */
     public long runScheduledPendingTasks() {
         try {
             return embeddedEventLoop().runScheduledTasks();
         } catch (Exception e) {
             recordException(e);
             return embeddedEventLoop().nextScheduledTask();
         }
     }
 
     private void recordException(ChannelFuture future) {
         if (!future.isSuccess()) {
             recordException(future.cause());
         }
     }
 
     private void recordException(Throwable cause) {
         if (lastException == null) {
             lastException = cause;
         } else {
             logger.warn(
                     "More than one exception was raised. " +
                             "Will report only the first one and log others.", cause);
         }
     }
 
     private EmbeddedEventLoop.FreezableTicker freezableTicker() {
         Ticker ticker = eventLoop().ticker();
         if (ticker instanceof EmbeddedEventLoop.FreezableTicker) {
             return (EmbeddedEventLoop.FreezableTicker) ticker;
         } else {
             throw new IllegalStateException(
                     "EmbeddedChannel constructed with custom ticker, time manipulation methods are unavailable.");
         }
     }
 
     /**
      * Advance the clock of the event loop of this channel by the given duration. Any scheduled tasks will execute
      * sooner by the given time (but {@link #runScheduledPendingTasks()} still needs to be called).
      */
     public void advanceTimeBy(long duration, TimeUnit unit) {
         freezableTicker().advance(duration, unit);
     }
 
     /**
      * Freeze the clock of this channel's event loop. Any scheduled tasks that are not already due will not run on
      * future {@link #runScheduledPendingTasks()} calls. While the event loop is frozen, it is still possible to
      * {@link #advanceTimeBy(long, TimeUnit) advance time} manually so that scheduled tasks execute.
      */
     public void freezeTime() {
         freezableTicker().freezeTime();
     }
 
     /**
      * Unfreeze an event loop that was {@link #freezeTime() frozen}. Time will continue at the point where
      * {@link #freezeTime()} stopped it: if a task was scheduled ten minutes in the future and {@link #freezeTime()}
      * was called, it will run ten minutes after this method is called again (assuming no
      * {@link #advanceTimeBy(long, TimeUnit)} calls, and assuming pending scheduled tasks are run at that time using
      * {@link #runScheduledPendingTasks()}).
      */
     public void unfreezeTime() {
         freezableTicker().unfreezeTime();
     }
 
     /**
      * Checks for the presence of an {@link Exception}.
      */
     private ChannelFuture checkException(ChannelPromise promise) {
       Throwable t = lastException;
       if (t != null) {
         lastException = null;
 
         if (promise.isVoid()) {
             PlatformDependent.throwException(t);
         }
 
         return promise.setFailure(t);
       }
 
       return promise.setSuccess();
     }
 
     /**
      * Check if there was any {@link Throwable} received and if so rethrow it.
      */
     public void checkException() {
       checkException(voidPromise());
     }
 
     /**
      * Returns {@code true} if the {@link Channel} is open and records optionally
      * an {@link Exception} if it isn't.
      */
     private boolean checkOpen(boolean recordException) {
         if (!isOpen()) {
           if (recordException) {
               recordException(new ClosedChannelException());
           }
           return false;
       }
 
       return true;
     }
 
     private EmbeddedEventLoop embeddedEventLoop() {
         if (isRegistered()) {
             return (EmbeddedEventLoop) super.eventLoop();
         }
 
         return loop;
     }
 
     /**
      * Ensure the {@link Channel} is open and if not throw an exception.
      */
     protected final void ensureOpen() {
         if (!checkOpen(true)) {
             checkException();
         }
     }
 
     @Override
     protected boolean isCompatible(EventLoop loop) {
         return loop instanceof EmbeddedEventLoop;
     }
 
     @Override
     protected SocketAddress localAddress0() {
         return isActive()? LOCAL_ADDRESS : null;
     }
 
     @Override
     protected SocketAddress remoteAddress0() {
         return isActive()? REMOTE_ADDRESS : null;
     }
 
     @Override
     protected void doRegister() throws Exception {
         state = State.ACTIVE;
     }
 
     @Override
     protected void doBind(SocketAddress localAddress) throws Exception {
         // NOOP
     }
 
     @Override
     protected void doDisconnect() throws Exception {
         if (!metadata.hasDisconnect()) {
             doClose();
         }
     }
 
     @Override
     protected void doClose() throws Exception {
         state = State.CLOSED;
     }
 
     @Override
     protected void doBeginRead() throws Exception {
         // NOOP
     }
 
     @Override
     protected AbstractUnsafe newUnsafe() {
         return new EmbeddedUnsafe();
     }
 
     @Override
     public Unsafe unsafe() {
         return ((EmbeddedUnsafe) super.unsafe()).wrapped;
     }
 
     @Override
     protected void doWrite(ChannelOutboundBuffer in) throws Exception {
         for (;;) {
             Object msg = in.current();
             if (msg == null) {
                 break;
             }
 
             ReferenceCountUtil.retain(msg);
             handleOutboundMessage(msg);
             in.remove();
         }
     }
 
     /**
      * Called for each outbound message.
      *
      * @see #doWrite(ChannelOutboundBuffer)
      */
     protected void handleOutboundMessage(Object msg) {
         outboundMessages().add(msg);
     }
 
     /**
      * Called for each inbound message.
      */
     protected void handleInboundMessage(Object msg) {
         inboundMessages().add(msg);
     }
 
     public static Builder builder() {
         return new Builder();
     }
 
     public static final class Builder {
         Channel parent;
         ChannelId channelId = EmbeddedChannelId.INSTANCE;
         boolean register = true;
         boolean hasDisconnect;
         //you should use either handlers or handler variable, but not both.
         ChannelHandler[] handlers = EMPTY_HANDLERS;
         ChannelHandler handler;
         ChannelConfig config;
         Ticker ticker;
 
         private Builder() {
         }
 
         /**
          * The parent {@link Channel} of this {@link EmbeddedChannel}.
          *
          * @param parent the parent {@link Channel} of this {@link EmbeddedChannel}.
          * @return This builder
          */
         public Builder parent(Channel parent) {
             this.parent = parent;
             return this;
         }
 
         /**
          * The {@link ChannelId} that will be used to identify this channel.
          *
          * @param channelId the {@link ChannelId} that will be used to identify this channel
          * @return This builder
          */
         public Builder channelId(ChannelId channelId) {
             this.channelId = Objects.requireNonNull(channelId, "channelId");
             return this;
         }
 
         /**
          * {@code true} if this {@link Channel} is registered to the {@link EventLoop} in the constructor. If
          * {@code false} the user will need to call {@link #register()}.
          *
          * @param register {@code true} if this {@link Channel} is registered to the {@link EventLoop} in the
          *                 constructor. If {@code false} the user will need to call {@link #register()}.
          * @return This builder
          */
         public Builder register(boolean register) {
             this.register = register;
             return this;
         }
 
         /**
          * {@code false} if this {@link Channel} will delegate {@link #disconnect()} to {@link #close()}, {@code true}
          * otherwise.
          *
          * @param hasDisconnect {@code false} if this {@link Channel} will delegate {@link #disconnect()} to
          *                      {@link #close()}, {@code true} otherwise
          * @return This builder
          */
         public Builder hasDisconnect(boolean hasDisconnect) {
             this.hasDisconnect = hasDisconnect;
             return this;
         }
 
         /**
          * The {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}.
          *
          * @param handlers the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
          * @return This builder
          */
         public Builder handlers(ChannelHandler... handlers) {
             this.handlers = Objects.requireNonNull(handlers, "handlers");
             this.handler = null;
             return this;
         }
 
         /**
          * The {@link ChannelHandler} which will be added to the {@link ChannelPipeline}.
          *
          * @param handler the {@link ChannelHandler}s which will be added to the {@link ChannelPipeline}
          * @return This builder
          */
         public Builder handlers(ChannelHandler handler) {
             this.handler = Objects.requireNonNull(handler, "handler");
             this.handlers = null;
             return this;
         }
 
         /**
          * The {@link ChannelConfig} which will be returned by {@link #config()}.
          *
          * @param config the {@link ChannelConfig} which will be returned by {@link #config()}
          * @return This builder
          */
         public Builder config(ChannelConfig config) {
             this.config = Objects.requireNonNull(config, "config");
             return this;
         }
 
         /**
          * Configure a custom ticker for this event loop.
          *
          * @param ticker The custom ticker
          * @return This builder
          */
         public Builder ticker(Ticker ticker) {
             this.ticker = ticker;
             return this;
         }
 
         /**
          * Create the channel. If you wish to extend {@link EmbeddedChannel}, please use the
          * {@link #EmbeddedChannel(Builder)} constructor instead.
          *
          * @return The channel
          */
         public EmbeddedChannel build() {
             return new EmbeddedChannel(this);
         }
     }
 
     private final class EmbeddedUnsafe extends AbstractUnsafe {
 
         // Delegates to the EmbeddedUnsafe instance but ensures runPendingTasks() is called after each operation
         // that may change the state of the Channel and may schedule tasks for later execution.
         final Unsafe wrapped = new Unsafe() {
             @Override
             public RecvByteBufAllocator.Handle recvBufAllocHandle() {
                 return EmbeddedUnsafe.this.recvBufAllocHandle();
             }
 
             @Override
             public SocketAddress localAddress() {
                 return EmbeddedUnsafe.this.localAddress();
             }
 
             @Override
             public SocketAddress remoteAddress() {
                 return EmbeddedUnsafe.this.remoteAddress();
             }
 
             @Override
             public void register(EventLoop eventLoop, ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.register(eventLoop, promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void bind(SocketAddress localAddress, ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.bind(localAddress, promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.connect(remoteAddress, localAddress, promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void disconnect(ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.disconnect(promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void close(ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.close(promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void closeForcibly() {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.closeForcibly();
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void deregister(ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.deregister(promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void beginRead() {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.beginRead();
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void write(Object msg, ChannelPromise promise) {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.write(msg, promise);
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public void flush() {
                 executingStackCnt++;
                 try {
                     EmbeddedUnsafe.this.flush();
                 } finally {
                     executingStackCnt--;
                     maybeRunPendingTasks();
                 }
             }
 
             @Override
             public ChannelPromise voidPromise() {
                 return EmbeddedUnsafe.this.voidPromise();
             }
 
             @Override
             public ChannelOutboundBuffer outboundBuffer() {
                 return EmbeddedUnsafe.this.outboundBuffer();
             }
         };
 
         @Override
         public void connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
             safeSetSuccess(promise);
         }
     }
 
     private final class EmbeddedChannelPipeline extends DefaultChannelPipeline {
         EmbeddedChannelPipeline(EmbeddedChannel channel) {
             super(channel);
         }
 
         @Override
         protected void onUnhandledInboundException(Throwable cause) {
             recordException(cause);
         }
 
         @Override
         protected void onUnhandledInboundMessage(ChannelHandlerContext ctx, Object msg) {
             handleInboundMessage(msg);
         }
     }
 }