在 Task.run 之外执行方法

Question

Call a method outside of Task.Run(). I have this code

 private void StartListening(int numPort, int tasknumber)
    {
        udpClients[tasknumber] = new UdpClient();
        udpClients[tasknumber].Client.Bind(new IPEndPoint(IPAddress.Any, numPort));
        iPEndPoints[tasknumber] = new IPEndPoint(0, 0);
        Task.Run(() =>
        {
            while (true)
            {
                AddUniqueRoomList(iPEndPoints[tasknumber].Address.ToString(), Encoding.UTF8.GetString(udpClients[tasknumber].Receive(ref iPEndPoints[tasknumber])));
            }
        });

    }

The code waits for a broadcast message then send a string to AddUniqueRoomList. What I want is just send a message to AddUniqueRoomList method without including it in Task.Run. AddUniqueRoomList method creates a UI button which causes an error if it's inside a task.run() cause unity doesn't do well with multithreading.

Answer 1

As in the comments you can use an often referred to as "dispatcher" in order to let any Action be executed in the Unity main thread.

The simplest way is actually to directly use a thread-save ConcurrentQueue<Action> which doesn't require locks like

public class MainThreadDispatcher : MonoBehaviour
{
    // Singleton pattern
    private static MainThreadDispatcher _instance;

    // This thread-save queue stores Actions to be executed in the main thread
    // any thread can add Actions to it via the ExecuteInUpdate method
    // then the existing actions will be executed in the Update loop
    // in the same order they came in
    private readonly ConcurrentQueue<Action> actions = new ConcurrentQueue<Action>();

    // This may be called by threads
    public static void ExecuteInUpdate(Action action)
    {
        if(!_instance)
        {
            Debug.LogError("You can talk but nobody is listening../nNo MainThreadDispatcher in scene!");
            return;
        }

        // Add the action as new entry at the end of the queue
        _instance.actions.Enqueue(action);
    }

    // Initialize the singleton
    private void Awake()
    {
        if(_instance && _instance != this)
        {
            // an instance already exists so destroy this one
            Destroy(gameObject);
            return;
        }

        _instance = this;
        DontDestroyOnLoad(this);
    }

    // This will be executed when the game is started
    // AFTER all Awake calls
    // See https://docs.unity3d.com/ScriptReference/RuntimeInitializeOnLoadMethodAttribute.html
    [RuntimeInitializeOnLoadMethod]
    private static void Initialize()
    {
        // If the instance exists already everything is fine
        if(_instance) return;

        // otherwise create it lazy
        // This adds a new GameObject to the scene with the MainThreadDispatcher
        // component attached -> this will call Awake automatically
        new GameObject("MainThreadDispatcher", typeof(MainThreadDispatcher));
    }

    // Executed in the Unity main thread
    private void Update()
    {
        // Every frame check if any actions are enqueued to be executed
        while(actions.TryDequeue(out car action)
        {
            action?.Invoke();
        }
    }
}

Put this script on any active object in the scene so it's Update is allways called.

Then in your script you wouldn't execute the method directly but rather add it to this queue by doing

private void StartListening(int numPort, int tasknumber)
{
    udpClients[tasknumber] = new UdpClient();
    udpClients[tasknumber].Client.Bind(new IPEndPoint(IPAddress.Any, numPort));
    iPEndPoints[tasknumber] = new IPEndPoint(0, 0);
    Task.Run(() =>
    {
        while (true)
        {
            var receivedString = Encoding.UTF8.GetString(udpClients[tasknumber].Receive(ref iPEndPoints[tasknumber]));
            var address = iPEndPoints[tasknumber].Address.ToString();

            MainThreadDispatcher.ExexuteInUpdate(
                () => 
                { 
                    AddUniqueRoomList(address, receivedString);
                }
            );

        }
    });
}