Invoking a function in main thread via background thread in Unity

Question

I'm using the following code to retrieve data from the server in the background.

new Thread(retrieveData()).Start();

Following is the function that receives the data from the server,

void retrieveData()
{
    while (true)
    {
        string data = subSocket.ReceiveFrameString();
       
    }
}

I want to create a prefab based on the data that was received from the server. Unfortunately, I can not do so from the background thread that is using retrieveData. How can I send a callback to the mainthread and create a prefab at the specified position?

Answer 1

There are multiple ways probably.

The most commonly used is a so called "Main Thread Dispatcher" pattern which might look like e.g.

// An object used to LOCK for thread safe accesses
private readonly object _lock = new object();
// Here we will add actions from the background thread
// that will be "delayed" until the next Update call => Unity main thread
private readonly Queue<Action> _mainThreadActions = new Queue<Action>();

private void Update () 
{
    // Lock for thread safe access 
    lock(_lock)
    {
        // Run all queued actions in order and remove them from the queue
        while(_mainThreadActions.Count > 0)
        {
            var action = _mainThreadActions.Dequeue();

            action?.Invoke();
        }
    }
}

void retrieveData()
{
    while (true)
    {
        var data = subSocket.ReceiveFrameString();
   

        // Any additional parsing etc that can still be done on the background thread

        // Lock for thread safe access
        lock(_lock)
        {
            // Add an action that requires the main thread
           _mainThreadActions.Enqueue(() =>
            {
                // Something that needs to be done on the main thread e.g.
                var text = new GameObject("Info").AddComponent<Text>();
                text.text = Data;
            }
        }
    }
}