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二、consumer端心跳机制
//创建ExchangeClient，对第一次服务发现providers路径下的相关url建立长连接 -->getClients(URL url) -->getSharedClient(URL url) -->ExchangeClient exchangeClient = initClient(url) -->Exchangers.connect(url, requestHandler) -->HeaderExchanger.connect(URL url, ExchangeHandler handler) -->new DecodeHandler(new HeaderExchangeHandler(handler))) -->Transporters.connect(URL url, ChannelHandler... handlers) -->NettyTransporter.connect(URL url, ChannelHandler listener) -->new NettyClient(url, listener) -->new MultiMessageHandler(HeartbeatHandler(AllChannelHandler(handler))) -->getChannelCodec(url)//获取Codec2，这里是DubboCountCodec实例 -->doOpen()//开启netty客户端 -->doConnect()//连接服务端，建立长连接 -->new HeaderExchangeClient(Client client, boolean needHeartbeat)//上述的NettyClient实例，needHeartbeat：true -->startHeatbeatTimer()//启动心跳计数器
客户端在initClient(url)中设置了heartbeat参数（默认为60s，用户自己设置的方式见“一”中所讲），如下：
1 /**
2 * Create new connection
3 */
4 private ExchangeClient initClient(URL url) {
5 ...
6 // enable heartbeat by default
7 url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.DEFAULT_HEARTBEAT));
8
9 ...
10
11 ExchangeClient client;
12 try {
13 // connection should be lazy
14 if (url.getParameter(Constants.LAZY_CONNECT_KEY, false)) {
15 client = new LazyConnectExchangeClient(url, requestHandler);16 } else {
17 client = Exchangers.connect(url, requestHandler);
18 }
19 } catch (RemotingException e) {
20 throw new RpcException("Fail to create remoting client for service(" + url + "): " + e.getMessage(), e);
21 }
22 return client;
23 }与provider类似，来看一下最后开启心跳检测的地方。
1 public class HeaderExchangeClient implements ExchangeClient {
2 private static final ScheduledThreadPoolExecutor scheduled = new ScheduledThreadPoolExecutor(2, new NamedThreadFactory("dubbo-remoting-client-heartbeat", true));
3 private final Client client;
4 private final ExchangeChannel channel;
5 // heartbeat timer
6 private ScheduledFuture<?> heartbeatTimer;
7 // heartbeat(ms), default value is 0 , won't execute a heartbeat.
8 private int heartbeat;
9 private int heartbeatTimeout;
10
11 public HeaderExchangeClient(Client client, boolean needHeartbeat) {
12 if (client == null) {
13 throw new IllegalArgumentException("client == null");
14 }
15 this.client = client;
16 this.channel = new HeaderExchangeChannel(client);
17 String dubbo = client.getUrl().getParameter(Constants.DUBBO_VERSION_KEY);
18 this.heartbeat = client.getUrl().getParameter(Constants.HEARTBEAT_KEY, dubbo != null && dubbo.startsWith("1.0.") ? Constants.DEFAULT_HEARTBEAT : 0);
19 this.heartbeatTimeout = client.getUrl().getParameter(Constants.HEARTBEAT_TIMEOUT_KEY, heartbeat * 3);
20 if (heartbeatTimeout < heartbeat * 2) {
21 throw new IllegalStateException("heartbeatTimeout < heartbeatInterval * 2");
22 }
23 if (needHeartbeat) {
24 startHeatbeatTimer();
25 }
26 }
27
28 private void startHeatbeatTimer() {
29 stopHeartbeatTimer();
30 if (heartbeat > 0) {
31 heartbeatTimer = scheduled.scheduleWithFixedDelay(
32 new HeartBeatTask(new HeartBeatTask.ChannelProvider() {
33 public Collection<Channel> getChannels() {
34 return Collections.<Channel>singletonList(HeaderExchangeClient.this);
35 }
36 }, heartbeat, heartbeatTimeout),
37 heartbeat, heartbeat, TimeUnit.MILLISECONDS);
38 }
39 }
40
41 private void stopHeartbeatTimer() {
42 if (heartbeatTimer != null && !heartbeatTimer.isCancelled()) {
43 try {
44 heartbeatTimer.cancel(true);
45 scheduled.purge();
46 } catch (Throwable e) {
47 if (logger.isWarnEnabled()) {
48 logger.warn(e.getMessage(), e);
49 }
50 }
51 }
52 heartbeatTimer = null;
53 }
54 }主要看一下startHeartbeatTimer()方法，与provider相同，只是provider是获取NettyServer的所有的NettyChannel，而consumer只是获取当前的对象。
consumer的handler处理链与provider完全相同。
最后来看一下consumer的重连机制：AbstractClient#reconnect
1 public void reconnect() throws RemotingException {
2 disconnect(); 3 connect();
4 }
5
6 public void disconnect() {
7 connectLock.lock();
8 try {
9 destroyConnectStatusCheckCommand();
10 try {
11 Channel channel = getChannel();
12 if (channel != null) {
13 channel.close();
14 }
15 } catch (Throwable e) {
16 logger.warn(e.getMessage(), e);
17 }
18 try {
19 doDisConnect();
20 } catch (Throwable e) {
21 logger.warn(e.getMessage(), e);
22 }
23 } finally {
24 connectLock.unlock();
25 }
26 }
27
28 protected void connect() throws RemotingException {
29 connectLock.lock();
30 try {
31 if (isConnected()) {
32 return;
33 }
34 initConnectStatusCheckCommand();
35 doConnect();
36 if (!isConnected()) {
37 throw new RemotingException(this, "Failed connect to server " + getRemoteAddress() + " from " + getClass().getSimpleName() + " "
38 + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion()
39 + ", cause: Connect wait timeout: " + getTimeout() + "ms.");
40 } else {
41 if (logger.isInfoEnabled()) {
42 logger.info("Successed connect to server " + getRemoteAddress() + " from " + getClass().getSimpleName() + " "
43 + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion()
44 + ", channel is " + this.getChannel());
45 }
46 }
47 reconnect_count.set(0);
48 reconnect_error_log_flag.set(false);
49 } catch (RemotingException e) {
50 throw e;
51 } catch (Throwable e) {
52 throw new RemotingException(this, "Failed connect to server " + getRemoteAddress() + " from " + getClass().getSimpleName() + " "
53 + NetUtils.getLocalHost() + " using dubbo version " + Version.getVersion()
54 + ", cause: " + e.getMessage(), e);
55 } finally {
56 connectLock.unlock();
57 }
58 }代码比较简单，先断连，再连接。
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