我正在使用HiveMQ Client（Java中的MQTT开源实现）编写程序，其中涉及使用两个多线程客户端。一个客户端被指定为发布者，另一个客户端被指定为订阅者（我知道我可以让同一客户端同时发布和订阅）。我正在尝试设计一个测试，其中发布者向客户端发送100条消息。目的是确定发送和接收所有消息所花费的时间。我意识到，如果我想确定接收消息要花费多长时间，则需要让订阅线程等待发布线程准备好发送消息。我决定使用wait（）和notify（），但似乎无法正确实现。我知道您需要使用与尝试相同的对象，但是我无法获得正确的设计。我在代码中为两个客户端的两个run方法添加了狙击手。 CommonThread.java实际上不是线程，并且我没有运行它，但是我试图在类之间使用它，以便能够wait（）和notify（），但是我丢失了一些东西。
HiveMQ：
https://github.com/hivemq/hivemq-community-edition
https://github.com/hivemq/hivemq-mqtt-client
SubMainThread.java：
public void run() {
// Creates the client object using Blocking API
Mqtt5BlockingClient subscriber = Mqtt5Client.builder()
.identifier(UUID.randomUUID().toString()) // the unique identifier of the MQTT client. The ID is randomly generated between
.serverHost("localhost") // the host name or IP address of the MQTT server. Kept it localhost for testing. localhost is default if not specified.
.serverPort(1883) // specifies the port of the server
.addConnectedListener(context -> ClientConnectionRetreiver.printConnected("Subscriber1")) // prints a string that the client is connected
.addDisconnectedListener(context -> ClientConnectionRetreiver.printDisconnected("Subscriber1")) // prints a string that the client is disconnected
.buildBlocking(); // creates the client builder
subscriber.connect(); // connects the client
ClientConnectionRetreiver.getConnectionInfo(subscriber); // gets connection info
try {
Mqtt5Publishes receivingClient1 = subscriber.publishes(MqttGlobalPublishFilter.ALL); // creates a "publishes" instance thats used to queue incoming messages // .ALL - filters all incoming Publish messages
subscriber.subscribeWith()
.topicFilter(subscriberTopic)
.qos(MqttQos.EXACTLY_ONCE)
.send();
PubSubUtility.printSubscribing("Subscriber1");
System.out.println("Publisher ready to send: " + PubMainThread.readyToSend);
x.threadCondWait(); // <<<<< HOW TO MAKE THIS WORK
System.out.println("Back to the normal execution flow :P");
startTime = System.currentTimeMillis();
System.out.println("Timer started");
for (int i = 1; i <= messageNum; i++) {
Mqtt5Publish receivedMessage = receivingClient1.receive(MESSAGEWAITTIME,TimeUnit.SECONDS).get(); // receives the message using the "publishes" instance waiting up to 5 minutes // .get() returns the object if available or throws a NoSuchElementException
PubSubUtility.convertMessage(receivedMessage); // Converts a Mqtt5Publish instance to string and prints
}
endTime = System.currentTimeMillis();
finalTime = endTime - startTime;
System.out.println( finalTime + PubMainThread.finalTime + " milliseconds");
finalSecTime = TimeUnit.MILLISECONDS.toSeconds(finalTime);
System.out.println(finalSecTime + PubMainThread.finalSecTime);
}
catch (InterruptedException e) { // Catches interruptions in the thread
LOGGER.log(Level.SEVERE, "The thread was interrupted while waiting for a message to be received", e);
}
catch (NoSuchElementException e){
System.out.println("There are no received messages"); // Handles when a publish instance has no messages
}
subscriber.disconnect();
}
PubMainThread.java：
public void run() {
// Creates the client object using Blocking API
Mqtt5BlockingClient publisher = Mqtt5Client.builder()
.identifier(UUID.randomUUID().toString()) // the unique identifier of the MQTT client. The ID is randomly generated between
.serverHost("localhost") // the host name or IP address of the MQTT server. Kept it localhost for testing. localhost is default if not specified.
.serverPort(1883) // specifies the port of the server
.addConnectedListener(context -> ClientConnectionRetreiver.printConnected("Publisher1")) // prints a string that the client is connected
.addDisconnectedListener(context -> ClientConnectionRetreiver.printDisconnected("Publisher1")) // prints a string that the client is disconnected
.buildBlocking(); // creates the client builder
publisher.connect(); // connects the client
ClientConnectionRetreiver.getConnectionInfo(publisher); // gets connection info
PubSubUtility.printPublising("Publisher1");
readyToSend = true;
x.threadCondNotify(); <<<<< HOW TO MAKE THIS WORK
// Think about making the PubClient Thread sleep for a short while so its not too ahead of the client
startTime = System.currentTimeMillis();
for (int i = 1; i <= messageNum; i++) {
publisher.publishWith()
.topic(publisherTopic) // publishes to the specified topic
.qos(MqttQos.EXACTLY_ONCE)
.payload(convertedMessage) // the contents of the message
.send();
}
endTime = System.currentTimeMillis();
finalTime = endTime - startTime;
finalSecTime = TimeUnit.MILLISECONDS.toSeconds(finalTime);
PubSubUtility.printNumOfPublished("Publisher1", messageNum);
publisher.disconnect();
}
公共类CommonThread {
private static final Logger LOGGER = Logger.getLogger(SubMainThread.class.getName()); // Creates a logger instance
public synchronized void threadCondNotify() {
notify();
System.out.println("Notified other thread");
}
public synchronized void threadCondWait() {
try {
while (PubMainThread.readyToSend != true) {
System.out.println("Waiting for another thread....");
wait();
}
}
catch (InterruptedException e) {
LOGGER.log(Level.SEVERE, "The thread was interrupted while waiting for another thread", e);
}
}
}
答案 0 :(得分：-1)
在Sender中（省略了一些详细信息的粗糙Java代码）：
//package statement and imports here
class Sender extends Thread {
public static final Boolean x= new Boolean(true);
public void run() {
//initialize here
synchronized(x) {
x.notify();
}
//send messages here
}
}
在Receiver中（在发送方之前开始）：
//package statement and imports here
class Receiver extends Thread {
public void run() {
//initialize here
synchronized(Sender.x) {
Sender.x.wait(); //blocks till Sender.x.notify()
}
Date start= new Date();
//receive messages here
Date end= new Date();
int duration_milliseconds= end.getTime()-start.getTime();
}
}
也许您必须添加
try{ /* code here */ } catch (InterruptedException e) {}
随时讨论直接使用notify（）和wait（）的意义和废话，尤其是在具有扩展并发库的Java版本中...