for #3666 add unit test more and docs

Author: tianliuliu

common/src/test/java/org/apache/rocketmq/common/MixAllTest.java

@@ -95,4 +95,16 @@ public void testGetLocalhostByNetworkInterface() throws Exception {
         assertThat(MixAll.LOCALHOST).isNotNull();
         assertThat(MixAll.getLocalhostByNetworkInterface()).isNotNull();
     }
+
+    @Test
+    public void testIsLmq() {
+        String testLmq = null;
+        assertThat(MixAll.isLmq(testLmq)).isFalse();
+        testLmq = "lmq";
+        assertThat(MixAll.isLmq(testLmq)).isFalse();
+        testLmq = "%LMQ%queue123";
+        assertThat(MixAll.isLmq(testLmq)).isTrue();
+        testLmq = "%LMQ%GID_TEST";
+        assertThat(MixAll.isLmq(testLmq)).isTrue();
+    }
 }

docs/cn/Example_LMQ.md

@@ -0,0 +1,75 @@
+# Light message queue (LMQ)
+
+
+## 一、broker启动配置
+
+
+broker.conf文件需要增加以下的配置项，开启LMQ开关，这样就可以识别LMQ相关属性的消息，进行原子分发消息到LMQ队列
+```properties
+enableLmq = true
+enableMultiDispatch = true
+```
+## 二、发送消息
+发送消息的时候通过设置 INNER_MULTI_DISPATCH 属性，LMQ queue使用逗号分割，queue前缀必须是 %LMQ%，这样broker就可以识别LMQ queue.
+```java
+DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
+producer.setNamesrvAddr("name-server1-ip:9876;name-server2-ip:9876");
+producer.start();
+
+
+/*
+* Create a message instance, specifying topic, tag and message body.
+*/
+Message msg = new Message("TopicTest" /* Topic */,
+                          "TagA" /* Tag */,
+                          ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) /* Message body */
+                         );
+/*
+* INNER_MULTI_DISPATCH property and PREFIX must start as "%LMQ%",
+* If it is multiple LMQ, need to use “,” split
+*/
+message.putUserProperty("INNER_MULTI_DISPATCH", "%LMQ%123,%LMQ%456");
+/*
+* Call send message to deliver message to one of brokers.
+*/
+SendResult sendResult = producer.send(msg);
+```
+## 三、拉取消息
+LMQ queue在每个broker上只有一个queue，也即queueId为0， 指明轻量级的MessageQueue，就可以拉取消息进行消费。
+```java
+DefaultMQPullConsumer defaultMQPullConsumer = new DefaultMQPullConsumer();
+defaultMQPullConsumer.setNamesrvAddr("name-server1-ip:9876;name-server2-ip:9876");
+defaultMQPullConsumer.setVipChannelEnabled(false);
+defaultMQPullConsumer.setConsumerGroup("CID_RMQ_SYS_LMQ_TEST");
+defaultMQPullConsumer.setInstanceName("CID_RMQ_SYS_LMQ_TEST");
+defaultMQPullConsumer.setRegisterTopics(new HashSet<>(Arrays.asList("TopicTest")));
+defaultMQPullConsumer.setBrokerSuspendMaxTimeMillis(2000);
+defaultMQPullConsumer.setConsumerTimeoutMillisWhenSuspend(3000);
+defaultMQPullConsumer.start();
+
+String brokerName = "set broker Name";
+MessageQueue mq = new MessageQueue("%LMQ%123", brokerName, 0);
+
+Long offset = defaultMQPullConsumer.maxOffset(mq);
+
+defaultMQPullConsumer.pullBlockIfNotFound(
+                mq, "*", offset, 32,
+                new PullCallback() {
+                    @Override
+                    public void onSuccess(PullResult pullResult) {
+                        List<MessageExt> list = pullResult.getMsgFoundList();
+                        if (list == null || list.isEmpty()) {
+                            return;
+                        }
+                        for (MessageExt messageExt : list) {
+                          
+                        }    
+                    }
+                    @Override
+                    public void onException(Throwable e) {
+                       
+                    }
+});
+```
+​
+