在RocketMQ客户端的DefaultMQPushConsumer的start方法被执行时，时不时会报出invokeSync call timeout异常，如下：
Caused by: java.lang.IllegalStateException: org.apache.rocketmq.remoting.exception.RemotingTimeoutException: invokeSync call timeout at org.apache.rocketmq.client.impl.factory.MQClientInstance.updateTopicRouteInfoFromNameServer(MQClientInstance.java:679) ~[rocketmq-client-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.impl.factory.MQClientInstance.updateTopicRouteInfoFromNameServer(MQClientInstance.java:509) ~[rocketmq-client-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl.updateTopicSubscribeInfoWhenSubscriptionChanged(DefaultMQPushConsumerImpl.java:872) ~[rocketmq-client-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl.start(DefaultMQPushConsumerImpl.java:653) ~[rocketmq-client-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.consumer.DefaultMQPushConsumer.start(DefaultMQPushConsumer.java:698) ~[rocketmq-client-4.7.1.jar:4.7.1] at cn.xdf.xcloud.rocketmq.support.DefaultRocketMQListenerContainer.start(DefaultRocketMQListenerContainer.java:276) ~[xcloud-rocketmq-core-1.2.0.RELEASE.jar:1.2.0.RELEASE] at cn.xdf.xcloud.rocketmq.autoconfigure.ListenerContainerConfiguration.registerContainer(ListenerContainerConfiguration.java:103) ~[xcloud-rocketmq-core-1.2.0.RELEASE.jar:1.2.0.RELEASE] ... 12 common frames omitted Caused by: org.apache.rocketmq.remoting.exception.RemotingTimeoutException: invokeSync call timeout at org.apache.rocketmq.remoting.netty.NettyRemotingClient.invokeSync(NettyRemotingClient.java:375) ~[rocketmq-remoting-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.impl.MQClientAPIImpl.getTopicRouteInfoFromNameServer(MQClientAPIImpl.java:1363) ~[rocketmq-client-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.impl.MQClientAPIImpl.getTopicRouteInfoFromNameServer(MQClientAPIImpl.java:1353) ~[rocketmq-client-4.7.1.jar:4.7.1] at org.apache.rocketmq.client.impl.factory.MQClientInstance.updateTopicRouteInfoFromNameServer(MQClientInstance.java:622) ~[rocketmq-client-4.7.1.jar:4.7.1] ... 18 common frames omitted如果着急马上找到解决办法，可以直接跳到解决办法。不过，授人以鱼，不如授之以渔。还是建议把寻找解决办法的过程看完，第一：可以给你以后遇到类似问题提供解决思路；第二：虽然都报这个异常，但产生的原因可能不一样。
寻找解决办法之路
做为面向搜索引擎编程的一员，立马复制关键字invokeSync call timeout去搜索引擎，得到的解决办法总结起来有两点：
- RocketMQ客户端和服务端版本不一致，检查了一下客户端和服务端的版本，都是4.7.1。
- 降低RocketMQ客户端的版本，这个我时不能接受的。
搜索引擎无法解决，只能自己想办法了。首先找到报异常的地方：
public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis) throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException { long beginStartTime = System.currentTimeMillis(); final Channel channel = this.getAndCreateChannel(addr); if (channel != null && channel.isActive()) { try { doBeforeRpcHooks(addr, request); long costTime = System.currentTimeMillis() - beginStartTime; if (timeoutMillis < costTime) { throw new RemotingTimeoutException("invokeSync call timeout"); } RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis - costTime); doAfterRpcHooks(RemotingHelper.parseChannelRemoteAddr(channel), request, response); return response; } //省略部分无关代码 } else { this.closeChannel(addr, channel); throw new RemotingConnectException(addr); } }原来是因为代码执行的时间过长，才报出了invokeSync call timeout异常。首先想到的是延长超时时间，继续分析源码，向上寻找调用方，发现在MQClientInstance的updateTopicRouteInfoFromNameServer方法中有：
topicRouteData = this.mQClientAPIImpl.getTopicRouteInfoFromNameServer(topic, 1000 * 3);居然是写死了3秒，没有办法修改，我竟无语凝噎。
再向下一步一步地分析源码，到底是哪里慢？
org.apache.rocketmq.remoting.netty.NettyRemotingClient.getAndCreateChannel org.apache.rocketmq.remoting.netty.NettyRemotingClient.getAndCreateNameserverChannel org.apache.rocketmq.remoting.netty.NettyRemotingClient.createChannel io.netty.bootstrap.Bootstrap.connect(java.net.SocketAddress) io.netty.bootstrap.Bootstrap.doResolveAndConnect io.netty.bootstrap.AbstractBootstrap.initAndRegister io.netty.bootstrap.ChannelFactory.newChannel io.netty.channel.socket.nio.NioSocketChannel.NioSocketChannel() io.netty.channel.nio.AbstractNioChannel.AbstractNioChannel io.netty.channel.AbstractChannel.AbstractChannel(io.netty.channel.Channel) io.netty.channel.AbstractChannel.newId io.netty.channel.DefaultChannelId.newInstance最终找到了：
public static DefaultChannelId newInstance() { return new DefaultChannelId(); }在创建DefaultChannelId的实例时，执行了这个类的静态代码块，就是这段静态代码块比较耗时。
那么，解决办法就有了，提前加载DefaultChannelId类，使其静态代码块先执行完成。
解决办法
在调用DefaultMQPushConsumer的start方法之前，插入如下代码：
DefaultChannelId.newInstance();
