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本文介绍普通消息的发送过程，事务消息在后面陈述。
发送消息入口
在测试代码中，DefaultMQProducerTest提供了消息发送的测试用例，可以看到，消息的发送由DefaultMQProducer完成，提供了多种发送入口，最终在DefaultMQProducerImpl.sendDefaultImpl进行。
sendDefaultImpl参数介绍
private SendResult sendDefaultImpl(
Message msg, // 消息体
final CommunicationMode communicationMode, // 发送方式，同步，异步，单向
final SendCallback sendCallback, // 回调
final long timeout // 超时时间
) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
}
具体实现
整体发送流程都写在注释中了
private SendResult sendDefaultImpl(
Message msg,
final CommunicationMode communicationMode,
final SendCallback sendCallback,
final long timeout
) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
this.makeSureStateOK();
Validators.checkMessage(msg, this.defaultMQProducer);
final long invokeID = random.nextLong();
long beginTimestampFirst = System.currentTimeMillis();
long beginTimestampPrev = beginTimestampFirst;
long endTimestamp = beginTimestampFirst;
/**
* 获取topic的发布信息
*/
TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());
if (topicPublishInfo != null && topicPublishInfo.ok()) {
boolean callTimeout = false;
MessageQueue mq = null;
Exception exception = null;
SendResult sendResult = null;
int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1;
int times = 0;
String[] brokersSent = new String[timesTotal];
/**
* 同步发送失败，重试
*/
for (; times < timesTotal; times++) {
String lastBrokerName = null == mq ? null : mq.getBrokerName();
/**
* 选择消息队列
*/
MessageQueue mqSelected = this.selectOneMessageQueue(topicPublishInfo, lastBrokerName);
if (mqSelected != null) {
mq = mqSelected;
brokersSent[times] = mq.getBrokerName();
try {
beginTimestampPrev = System.currentTimeMillis();
long costTime = beginTimestampPrev - beginTimestampFirst;
if (timeout < costTime) {
callTimeout = true;
break;
}
/**
* 发送消息
*/
sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout - costTime);
endTimestamp = System.currentTimeMillis();
/**
* 更新失败策略
*/
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false);
switch (communicationMode) {
case ASYNC:
return null;
case ONEWAY:
return null;
case SYNC:
if (sendResult.getSendStatus() != SendStatus.SEND_OK) {
if (this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) {
continue;
}
}
return sendResult;
default:
break;
}
} catch (RemotingException e) {
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, true);
log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e);
log.warn(msg.toString());
exception = e;
continue;
} catch (MQClientException e) {
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, true);
log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e);
log.warn(msg.toString());
exception = e;
continue;
} catch (MQBrokerException e) {
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, true);
log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e);
log.warn(msg.toString());
exception = e;
switch (e.getResponseCode()) {
case ResponseCode.TOPIC_NOT_EXIST:
case ResponseCode.SERVICE_NOT_AVAILABLE:
case ResponseCode.SYSTEM_ERROR:
case ResponseCode.NO_PERMISSION:
case ResponseCode.NO_BUYER_ID:
case ResponseCode.NOT_IN_CURRENT_UNIT:
continue;
default:
if (sendResult != null) {
return sendResult;
}
throw e;
}
} catch (InterruptedException e) {
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false);
log.warn(String.format("sendKernelImpl exception, throw exception, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e);
log.warn(msg.toString());
log.warn("sendKernelImpl exception", e);
log.warn(msg.toString());
throw e;
}
} else {
break;
}
}
if (sendResult != null) {
return sendResult;
}
String info = String.format("Send [%d] times, still failed, cost [%d]ms, Topic: %s, BrokersSent: %s",
times,
System.currentTimeMillis() - beginTimestampFirst,
msg.getTopic(),
Arrays.toString(brokersSent));
info += FAQUrl.suggestTodo(FAQUrl.SEND_MSG_FAILED);
MQClientException mqClientException = new MQClientException(info, exception);
if (callTimeout) {
throw new RemotingTooMuchRequestException("sendDefaultImpl call timeout");
}
if (exception instanceof MQBrokerException) {
mqClientException.setResponseCode(((MQBrokerException) exception).getResponseCode());
} else if (exception instanceof RemotingConnectException) {
mqClientException.setResponseCode(ClientErrorCode.CONNECT_BROKER_EXCEPTION);
} else if (exception instanceof RemotingTimeoutException) {
mqClientException.setResponseCode(ClientErrorCode.ACCESS_BROKER_TIMEOUT);
} else if (exception instanceof MQClientException) {
mqClientException.setResponseCode(ClientErrorCode.BROKER_NOT_EXIST_EXCEPTION);
}
throw mqClientException;
}
List<String> nsList = this.getmQClientFactory().getMQClientAPIImpl().getNameServerAddressList();
if (null == nsList || nsList.isEmpty()) {
throw new MQClientException(
"No name server address, please set it." + FAQUrl.suggestTodo(FAQUrl.NAME_SERVER_ADDR_NOT_EXIST_URL), null).setResponseCode(ClientErrorCode.NO_NAME_SERVER_EXCEPTION);
}
throw new MQClientException("No route info of this topic, " + msg.getTopic() + FAQUrl.suggestTodo(FAQUrl.NO_TOPIC_ROUTE_INFO),
null).setResponseCode(ClientErrorCode.NOT_FOUND_TOPIC_EXCEPTION);
}
下面对发送过程分别做介绍
获取topic的发布信息
消息的发送消费是基于topic的，TopicPublishInfo主要包含了topic对应的多个broker信息，多个Queue信息，以及filterServer等信息。
下面看如何获取
private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {
// 从本地缓存中读取
TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);
// 缓存中为空，从nameserver中获取
if (null == topicPublishInfo || !topicPublishInfo.ok()) {
this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());
// nameserver中的信息有变化，更新本地信息，详见内部逻辑
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
}
if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {
return topicPublishInfo;
} else {
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
return topicPublishInfo;
}
}
选择发送消息的队列
发送消息前，需要选择一个合适的消息队列，其中包含了容错策略，具体在MQFaultStrategy中定义：
public class MQFaultStrategy {
// 维护每个broker的发送延迟
private final LatencyFaultTolerance<String> latencyFaultTolerance = new LatencyFaultToleranceImpl();
// 容错开关，默认关闭
private boolean sendLatencyFaultEnable = false;
// 延迟级别数组
private long[] latencyMax = {50L, 100L, 550L, 1000L, 2000L, 3000L, 15000L};
// 不可用时长数组
private long[] notAvailableDuration = {0L, 0L, 30000L, 60000L, 120000L, 180000L, 600000L};
...
}
选择队列时，会根据sendLatencyFaultEnable进行选择：
- sendLatencyFaultEnable = true，在随机递增取模的基础上，过滤掉不可用的broker，这里的不可用为：如果broker上一次发送时间超过550ms，就对broker设置30000ms不可用，具体策略值为两个数组的对应值
- sendLatencyFaultEnable = false，随机递增取模获取一个MessageQueue
public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {
// 开启 sendLatencyFaultEnable
if (this.sendLatencyFaultEnable) {
try {
int index = tpInfo.getSendWhichQueue().getAndIncrement();
for (int i = 0; i < tpInfo.getMessageQueueList().size(); i++) {
int pos = Math.abs(index++) % tpInfo.getMessageQueueList().size();
if (pos < 0)
pos = 0;
MessageQueue mq = tpInfo.getMessageQueueList().get(pos);
// isAvailable 校验是否可用
if (latencyFaultTolerance.isAvailable(mq.getBrokerName())) {
if (null == lastBrokerName || mq.getBrokerName().equals(lastBrokerName))
return mq;
}
}
// 如果都不可用，从不可用的列表选择一个
final String notBestBroker = latencyFaultTolerance.pickOneAtLeast();
int writeQueueNums = tpInfo.getQueueIdByBroker(notBestBroker);
if (writeQueueNums > 0) {
final MessageQueue mq = tpInfo.selectOneMessageQueue();
if (notBestBroker != null) {
mq.setBrokerName(notBestBroker);
mq.setQueueId(tpInfo.getSendWhichQueue().getAndIncrement() % writeQueueNums);
}
return mq;
} else {
latencyFaultTolerance.remove(notBestBroker);
}
} catch (Exception e) {
log.error("Error occurred when selecting message queue", e);
}
return tpInfo.selectOneMessageQueue();
}
// 不开启 sendLatencyFaultEnable
return tpInfo.selectOneMessageQueue(lastBrokerName);
}
发送消息
之后就是消息发送了，调用sendKernelImpl()通过之前文章介绍的通信模块来完成。具体为批量消息处理，压缩消息处理，前置Hook处理，构造requestHeader，发送消息，后置Hook处理等，具体自行查看源码即可
更新失败策略
消息发送成功后，更新消息发送测失败策略，即前面提到的MQFaultStrategy，更新broker最近的发送耗时和延迟时间：
public void updateFaultItem(final String brokerName, final long currentLatency, boolean isolation) {
if (this.sendLatencyFaultEnable) {
long duration = computeNotAvailableDuration(isolation ? 30000 : currentLatency);
this.latencyFaultTolerance.updateFaultItem(brokerName, currentLatency, duration);
}
}
private long computeNotAvailableDuration(final long currentLatency) {
for (int i = latencyMax.length - 1; i >= 0; i--) {
if (currentLatency >= latencyMax[i])
return this.notAvailableDuration[i];
}
return 0;
}
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