缘起

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：

1. 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。
2. 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();

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