Unity as a simulation environment - delay the Update() loop while big calculation is performed

Question

I am quite new to Unity and i am currently using it as a tool for designing a simple simulated environment for my pilot research study. Here is a simplified explanation:

The main character (agent) scans the environment and sends the state (as a JSON object) via TCP socket to a python server.

On the python server side a big calculation is performed based on the the state. The result is an action that is being sent back via TCP to Unity.

The character needs to perform this action in Unity and then again scan the environment. The new state is sent again to the python server....

This process is being repeated 'till infinity (unless the client or server is stopped) eventually leading to the agent self-developing a behavior based on its learning.

I finished creating the environment in unity as well as programmed the learning algorithm in python. Moreover, i managed to establish TCP connection between the two. However, i stumbled across the problem of the main Update() loop in Unity.

Namely, if i simplify the process to Unity sending ping (being the state) and python sending pong (being the action) i need the following process to be repeated.

• freeze frame
• ping
• calculation
• pong
• next frame

So in the Unity Start() method i setup the socket and send the initial ping. What i would like in the main Update() loop is to make Unity wait for python's pong answer before updating the frame. I created a script containing a toy example and tried to simulate the calculation-time in python by adding 2 seconds of delay before sending the pong to Unity.

Here is the code for the Unity script (just attach it to the Main Camera):

 using UnityEngine;
 using System;
 using System.IO;
 using System.Net.Sockets;

 public class networkSocketPingPong : MonoBehaviour
 {
     public String host = "localhost";
     public Int32 port = 50000;

     internal Boolean socket_ready = false;
     internal String input_buffer = "";

     TcpClient tcp_socket;
     NetworkStream net_stream;

     StreamWriter socket_writer;
     StreamReader socket_reader;

     private void Start()
     {
         setupSocket();
         writeSocket("ping");
     }


      void Update()
      {

         string received_data = readSocket();

         switch (received_data)
              {
                  case "pong":
                      Debug.Log("Python controller sent: " + (string)received_data);
                      writeSocket("ping");
                      break;
                  default:
                      Debug.Log("Nothing received from Python");
                      break;
          }
     }

     void OnApplicationQuit()
     {
         closeSocket();
     }

     // Helper methods for:
     //...setting up the communication
     public void setupSocket()
     {
         try
         {
             tcp_socket = new TcpClient(host, port);
             net_stream = tcp_socket.GetStream();
             socket_writer = new StreamWriter(net_stream);
             socket_reader = new StreamReader(net_stream);
             socket_ready = true;
         }
         catch (Exception e)
         {
             // Something went wrong
             Debug.Log("Socket error: " + e);
         }
     }

     //... writing to a socket...
     public void writeSocket(string line)
     {
         if (!socket_ready)
             return;

         socket_writer.Write(line);
         socket_writer.Flush();
     }

     //... reading from a socket...
     public String readSocket()
     {
        if (!socket_ready)
         {
             Debug.Log("Socket is not ready");
             return "";
         }

         if (net_stream.DataAvailable)
             return socket_reader.ReadLine();

         return "";
     }

     //... closing a socket...
     public void closeSocket()
     {
         if (!socket_ready)
             return;

         socket_writer.Close();
         socket_reader.Close();
         tcp_socket.Close();
         socket_ready = false;
     }
 }

...and here is the python server code:

 import socket
 import time

 host = 'localhost' 
 port = 50000
 backlog = 5 
 size = 1024 
 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
 s.bind((host,port)) 
 s.listen(backlog) 

 while 1:
     client, address = s.accept() 
     print "Client connected."
     while 1:
         data = client.recv(size)
         if data == "ping":
             time.sleep(2)
             print ("Unity Sent: " + str(data))
             client.send("pong\n")
         else:
             client.send("Bye!")
             print ("Unity Sent Something Else: " + str(data))
             client.close()
             break

I first run the python server and then the simulation (via Unity editor). This results with the following console screenshot:

This proves that the main Update() loop is running while i want it to pause and update only when "pong" is received from the server. Any ideas how to achieve this?

I searched the forum for answers but always stumbled upon questions that ask for the opposite - how to make Unity not to freeze - and answers that suggest using Coroutines or Threads.

Any help will be much appreciated.

Thanks in advance!!!

Answer 1

I searched the forum for answers but always stumbled upon questions that ask for the opposite - how to make Unity not to freeze - and answers that suggest using Coroutines or Threads.

That's right. This was my initial thought too after your bulletin below:

• freeze frame
• ping
• calculation
• pong
• next frame

That translated into a code would be:

void Start()
{
    StartCoroutine(doForever());
}


IEnumerator doForever()
{

    while (true)
    {
        //freeze frame
        Time.timeScale = 0f;

        //ping
        writeSocket("ping");

        //calculation

        //pong
        string pongValue = socket_reader.ReadLine();

        //unfeeze frame
        Time.timeScale = 1f;

        //next frame
        yield return null;
    }
}

---

This is so wrong in many ways. This will freeze Unity when waiting or receiving data from python. This may be something you want but it's not good in any way.

You must do this in a Thread. The reason for this is because you are using the blocking version of the receive function.

Thread socketThread;

void Start()
{
    socketThread = new Thread(doForever);
    socketThread.IsBackground = true;
    socketThread.Start();
}

void doForever()
{

    while (true)
    {
        //freeze frame
        gameStatus = GameStatus.PAUSED;

        //ping
        writeSocket("ping");

        gameStatus = GameStatus.RUNNING;
        //calculation

        //pong
        string pongValue = socket_reader.ReadLine();
    }
}

If you want to use Unity's API in from another Thread or the code above you should look at this post.

Do not use read from socket from the main Thread like you are currently doing. One exception is when using the async functions but you are not in this case.

There are many reasons for this and the worst one is your UI not being responsive until you receive something from your python code.

---

As for pausing your game, you can simply use enum and if statement to accomplish that.

public enum GameStatus
{
    RUNNING, PAUSED
}

Then in every of your function that is noving something, you can do something like this:

GameStatus gameStatus;

void moveCharacterEveryFrame()
{
    if (gameStatus == GameStatus.PAUSED)
    {
        return;
    }

    //Move Character code below
}

When you want to pause your game from that Thread above, you just do this:

gameStatus = GameStatus.PAUSED;

To unpuse:

gameStatus = GameStatus.RUNNING;

Now, you don't freeze your Game or UI.

Answer 2

Delete your Update() function and add put your code to callback function of your WriteSocket() function.

Answer 3

You can use Coroutine to create Thread :

public Action<string> OnReceiveMessage;  // event trigger when receive message.

private Thread m_ReceiveThread;
private List<string> m_ReceiveStrings;
private int m_ReceiveStrCount;

private void Start() {
    m_ReceiveStrings = new List<string> ();
    m_ReceiveStrCount = m_ReceiveStrings.Count;
    StartCoroutine (CreateReceiveListener());
}

private IEnumerator CreateReceiveListener() {
    m_ReceiveThread = new Thread (ReceiveListener);
    m_ReceiveThread.IsBackground = true;
    m_ReceiveThread.Start ();
    yield return null;
}

Add to List a message:

private void ReceiveListener() {
    while (m_Connected) {
        string receiveData = ReadSocket ();
        if (string.IsNullOrEmpty (receiveData) == false) {
            m_ReceiveStrings.Add (receiveData);
            Debug.Log (receiveData);
        }
    }
}

Then check in lateupdate if have any change:

private void LateUpdate() {
    if (m_ReceiveStrCount != m_ReceiveStrings.Count) {
        if (OnReceiveMessage != null) {
            OnReceiveMessage (m_ReceiveStrings[m_ReceiveStrCount]);
            m_ReceiveStrCount = m_ReceiveStrings.Count;
        }
    }
}

Answer 4

If I understood correctly you want to hang the Unity's internal drawing mechanism till you receive new data from the server?

If that's the case then just wait for it in the Update or LateUpdate method :

void Update() // or void LateUpdate()
{
    while(!received && Application.isRunning){
        // do nothing
    }

    // receive
    string msg = readSocket();
    // log
    Debug.Log(msg);
}

But this is not how you should use Unity engine.

If that's not the thing you've wanted then put the comment and I'll remove this answer :)