Listening for incoming messages from TCP server causes StackOverflow

Question

I need to continuously listen for messages from my C# TCP server, so I do it in separate thread:

private void StartMessageReceivingLoop()
{       
    new Thread(){
        public void run()
        {
            String msg = null;

            try
            {
                msg = inputStream.readLine(); // inputStream is a BufferedReader instance.
            } 
            catch (IOException e)
            {
                e.printStackTrace();
            }

            if (msg != null && msg != "")
                NotifyAndForwardMessage(msg); // Notify listeners about the message.

            run(); // Next iteration.
        }
    }.start();
}

What's wrong with my approach? Why am I getting a StackOverflowError? I'm guessing that run() is invoked incredibly fast because BufferedReader.readLine() is non-blocking, but what can I do about it?

Well I could put `run()` contents in a `while` loop but there's really no difference, is there? — matt-pielat, Jan 04 '15 at 22:42
The difference is that the loop doesn't get a stack overflow. — user207421, Jan 04 '15 at 23:29

score 3 · Accepted Answer · answered Jan 04 '15 at 22:43

Don't call run() within run(). This is not a recursive function. If you want to keep reading until some condition, wrap this in a while loop. By calling the method you are executing while you are executing it, you are creating another stack frame. What you really want is just to loop.

public void run() {
   String msg = null;
   while(true) {  // Or whatever your exit condition is...
      try {
         msg = inputStream.readLine();
      } catch(IOException e) {
         // Handle properly.
      }
      if (msg != null && msg != "") {
          NotifyAndForwardMessage(msg);
      }
   }
}

To help illustrate, it kind of works like this...

Thread.start()
   + run() // 1 (called by thread)
      + run() // 2 (called by previous run)
         + run() //3 (called by previous run)
            +etc... where you'll eventually run out of stack space.

Another rookie mistake. Thanks for your explanation. – matt-pielat Jan 04 '15 at 22:48 — matt-pielat, Jan 04 '15 at 22:48

Listening for incoming messages from TCP server causes StackOverflow

1 Answers1