如何在MQTT消息到达之前保持线程

Question

In my app im sending a message via Paho MQTT and i have to wait for a response before sending new message.

eg:

while (!exit){
  sendMessage(); //sends message via Paho MQTT 
  myMqttConnection.run() //starts a thread to wait for Response via Paho MQTT
  //what to do to hold this thread till a message has arrived?
}

sendMessage() and myMqttConnection are 2 different topics in case that matters

Answer 1

There's a few ways to tackle this, given the limited information that you have provided.

If you have to spawn a thread in the myMqttConnection.run() code, you need a way for your Threads to wait for each other.

If you are happy with old-skool code, a shared guard object and a wait/notify mechanism would do it. The more modern way to do this is with something like a CyclicBarrier.

Otherwise, if you are spawning a thread in myMqttConnection.run() , but then you wait for it to complete, you have to question why you are spawning a thread..? Why not just rename run() to read() and return the message from the read() message.