[ROCKETMQ-324] Expose an interface for client to specify the async call back executor

client/src/main/java/org/apache/rocketmq/client/impl/producer/DefaultMQProducerImpl.java

@@ -1060,6 +1060,10 @@ public void endTransaction(
             this.defaultMQProducer.getSendMsgTimeout());
     }
 
+    public void setCallbackExecutor(final ExecutorService callbackExecutor) {
+        this.mQClientFactory.getMQClientAPIImpl().getRemotingClient().setCallbackExecutor(callbackExecutor);
+    }
+
     public SendResult send(Message msg,
         long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
         return this.sendDefaultImpl(msg, CommunicationMode.SYNC, null, timeout);

client/src/main/java/org/apache/rocketmq/client/producer/DefaultMQProducer.java

@@ -18,6 +18,7 @@
 
 import java.util.Collection;
 import java.util.List;
+import java.util.concurrent.ExecutorService;
 import org.apache.rocketmq.client.ClientConfig;
 import org.apache.rocketmq.client.QueryResult;
 import org.apache.rocketmq.client.Validators;
@@ -34,6 +35,7 @@
 import org.apache.rocketmq.common.message.MessageQueue;
 import org.apache.rocketmq.remoting.RPCHook;
 import org.apache.rocketmq.remoting.exception.RemotingException;
+import org.apache.rocketmq.remoting.netty.NettyRemotingClient;
 
 /**
  * This class is the entry point for applications intending to send messages.
@@ -630,6 +632,16 @@ public SendResult send(Collection<Message> msgs, MessageQueue messageQueue,
         return this.defaultMQProducerImpl.send(batch(msgs), messageQueue, timeout);
     }
 
+    /**
+     * Sets an Executor to be used for executing callback methods.
+     * If the Executor is not set, {@link NettyRemotingClient#publicExecutor} will be used.
+     *
+     * @param callbackExecutor the instance of Executor
+     */
+    public void setCallbackExecutor(final ExecutorService callbackExecutor) {
+        this.defaultMQProducerImpl.setCallbackExecutor(callbackExecutor);
+    }
+
     private MessageBatch batch(Collection<Message> msgs) throws MQClientException {
         MessageBatch msgBatch;
         try {

client/src/test/java/org/apache/rocketmq/client/producer/DefaultMQProducerTest.java

@@ -22,6 +22,8 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import org.apache.rocketmq.client.ClientConfig;
 import org.apache.rocketmq.client.exception.MQBrokerException;
 import org.apache.rocketmq.client.exception.MQClientException;
@@ -39,6 +41,7 @@
 import org.apache.rocketmq.common.protocol.route.QueueData;
 import org.apache.rocketmq.common.protocol.route.TopicRouteData;
 import org.apache.rocketmq.remoting.exception.RemotingException;
+import org.apache.rocketmq.remoting.netty.NettyRemotingClient;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -195,6 +198,22 @@ public void run() {
         }
     }
 
+    @Test
+    public void testSetCallbackExecutor() throws MQClientException {
+        String producerGroupTemp = producerGroupPrefix + System.currentTimeMillis();
+        producer = new DefaultMQProducer(producerGroupTemp);
+        producer.setNamesrvAddr("127.0.0.1:9876");
+        producer.start();
+
+        ExecutorService customized = Executors.newCachedThreadPool();
+        producer.setCallbackExecutor(customized);
+
+        NettyRemotingClient remotingClient = (NettyRemotingClient) producer.getDefaultMQProducerImpl()
+            .getmQClientFactory().getMQClientAPIImpl().getRemotingClient();
+
+        assertThat(remotingClient.getCallbackExecutor()).isEqualTo(customized);
+    }
+
     public static TopicRouteData createTopicRoute() {
         TopicRouteData topicRouteData = new TopicRouteData();
 

remoting/src/main/java/org/apache/rocketmq/remoting/RemotingClient.java

@@ -46,5 +46,7 @@ void invokeOneway(final String addr, final RemotingCommand request, final long t
     void registerProcessor(final int requestCode, final NettyRequestProcessor processor,
         final ExecutorService executor);
 
+    void setCallbackExecutor(final ExecutorService callbackExecutor);
+
     boolean isChannelWritable(final String addr);
 }

remoting/src/main/java/org/apache/rocketmq/remoting/netty/NettyRemotingClient.java

@@ -87,6 +87,11 @@ public class NettyRemotingClient extends NettyRemotingAbstract implements Remoti
     private final Lock lockNamesrvChannel = new ReentrantLock();
 
     private final ExecutorService publicExecutor;
+
+    /**
+     * Invoke the callback methods in this executor when process response.
+     */
+    private ExecutorService callbackExecutor;
     private final ChannelEventListener channelEventListener;
     private DefaultEventExecutorGroup defaultEventExecutorGroup;
     private RPCHook rpcHook;
@@ -582,7 +587,12 @@ public RPCHook getRPCHook() {
 
     @Override
     public ExecutorService getCallbackExecutor() {
-        return this.publicExecutor;
+        return callbackExecutor != null ? callbackExecutor : publicExecutor;
+    }
+
+    @Override
+    public void setCallbackExecutor(final ExecutorService callbackExecutor) {
+        this.callbackExecutor = callbackExecutor;
     }
 
     static class ChannelWrapper {

remoting/src/test/java/org/apache/rocketmq/remoting/netty/NettyRemotingClientTest.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.rocketmq.remoting.netty;
+
+import java.lang.reflect.Field;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.junit.MockitoJUnitRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(MockitoJUnitRunner.class)
+public class NettyRemotingClientTest {
+    private NettyRemotingClient remotingClient = new NettyRemotingClient(new NettyClientConfig());
+
+    @Test
+    public void testSetCallbackExecutor() throws NoSuchFieldException, IllegalAccessException {
+        Field field = NettyRemotingClient.class.getDeclaredField("publicExecutor");
+        field.setAccessible(true);
+        assertThat(remotingClient.getCallbackExecutor()).isEqualTo(field.get(remotingClient));
+
+        ExecutorService customized = Executors.newCachedThreadPool();
+        remotingClient.setCallbackExecutor(customized);
+
+        assertThat(remotingClient.getCallbackExecutor()).isEqualTo(customized);
+    }
+}