Working with threads: "can only be called from the main thread"

Dear All,
I'm a c++ programmer new to Unity and C#.
I implemented a Thread in a class that inherits from MonoBehaviour. In the Awake() method I get a specific GameObject from the scene and store it in a class member, then I start a server on a Thread.
Unexpectedly when the server callback is called the GameObject variable seems corrupted.

Here is a code snippet:

Code (CSharp):

1. public class ThriftService : MonoBehaviour, unity3Dservice.Iface
2. {
3.    private Thread workerThread = null;
4.    private GameObject fpsGameObject = null;
5.  
6.    public WidgetSetupData GetWidgetConfig(WGT_TYPE wgt)
7.    {
8.       WidgetSetupData data = new WidgetSetupData();
9.       data.Position = new WGT_Position();
10.       data.Position.X = fpsRectTransform.anchoredPosition.x;
11.       return data;
12.    }
13.  
14.    void Awake() {
15.       fpsGameObject = GameObject.FindGameObjectsWithTag("FpsDisplayCanvas")[0];
16.       startServerThread();
17.    }
18.  
19.    void startServerThread() {
20.       workerThread = new Thread(runServer);
21.       try {
22.          workerThread.Start();
23.       } catch (Exception e) {
24.          Debug.LogError(e.StackTrace);
25.       }
26.    }
27.  
28.    void runServer() {
29.       unity3Dservice.Processor processor = new unity3Dservice.Processor(this);
30.       TServerTransport serverTransport = new TServerSocket(unity3d_serviceConstants.unity3Dservice_port);
31.       server = new TSimpleServer(processor, serverTransport);
32.       server.Serve();
33.    }
34. }

GetWidgetConfig is the callback where "fpsRectTransform" is not a valid object.
On the Unity Console I get the error:

"INTERNAL_get_anchoredPosition can only be called from the main thread.
Constructors and field initializers will be executed from the loading thread when loading a scene.
Don't use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function.
UnityEngine.RectTransform:get_anchoredPosition()
ThriftService:GetWidgetConfig(WGT_TYPE) (at Assets/Scripting/ThriftService.cs:43)"

Can anybody explain me this behaviour and a suggested solution?

Best regards,
Gianni

 

You can't access the Unity API from any thread outside of the main execution thread of Unity.

If you need data from Unity for a thread, you'll need to gather said information as a token and pass it along to the thread.

Otherwise various people have created various tools that facilitate syncing back to the Unity thread to gather/set information from threads. But note this increase overhead as join the main thread and then leave it again.

 

I can't believe it!!! I thought Unity was out for years and it is still not thread safe?? That's a big limitation. Wake up Unity team!

 

soon

 

I found this helpful https://docs.unity3d.com/Manual/JobSystem.html

 

So, how would i fix that? I have the same issue but just with GetName. I have no idea what threads are and i am not working with them so i don't know why this happens.

 

i'm using this to call stuff from another thread,
https://github.com/PimDeWitte/UnityMainThreadDispatcher