OnLoadEventCompleted triggered twice if only host connected

[Dockyardb]

Description

When you start a server as an host and nobody else connects the OnLoadEventCompleted and OnSceneEvent with sceneEvent.SceneEventType = OnLoadEventCompleted gets triggered twice. If there is a connected client this wont happen.

Reproduce Steps

1. Host a server
2. Subscribe to the OnLoadEventCompleted
3. Change the Scene

Actual Outcome

It is triggered twice

Expected Outcome

It should only be triggered once.

Environment

• OS: Windows
• Unity Version: 2022.1.20f1
• Netcode Version: 1.1.0

[ashwinimurt]

MTT-5010

[NoelStephensUnity]

Hello @Dockyardb !
Before I start looking into this, I have a few questions:

• Is the server/host the only one that registers for NetworkSceneManager.OnSceneEvent?
• Does both the client and the server/host register for the NetworkSceneManager.OnLoadEventCompleted event?

If that is the case, then what you are experiencing is the correct default behavior..

If you register for OnSceneEvent, it will provide all SceneEventType notifications (some have additional information per SceneEventType).
If you register for OnLoadEventCompleted, it will only be invoked when a scene loading event has completed.

As an example:

public class MyNotificationBehaviour : NetworkBehaviour
{
    private void Awake()
    {
        NetworkManager.Singleton.OnServerStarted += Singleton_OnServerStarted;
    }

    private void Singleton_OnServerStarted()
    {
        // Check if only the server is registering for the OnSceneEvent notification
        // If so, this will receive all scene event notifications (including LoadEventCompleted)
        NetworkManager.SceneManager.OnSceneEvent += SceneManager_OnSceneEvent;
    }

    private void SceneManager_OnSceneEvent(SceneEvent sceneEvent)
    {
        if (sceneEvent.SceneEventType == SceneEventType.LoadEventCompleted)
        {
            Debug.Log("Server received LoadEventCompleted event via OnSceneEvent notification.");
        }
    }

    public override void OnNetworkSpawn()
    {
        // Here you should check if you are registering for OnLoadEventCompleted on both the server and client instances
        // If you don't, then both the server and client will receive this notification
        NetworkManager.SceneManager.OnLoadEventCompleted += SceneManager_OnLoadEventCompleted;
        base.OnNetworkSpawn();
    }

    private void SceneManager_OnLoadEventCompleted(string sceneName, UnityEngine.SceneManagement.LoadSceneMode loadSceneMode, System.Collections.Generic.List<ulong> clientsCompleted, System.Collections.Generic.List<ulong> clientsTimedOut)
    {
        var serverOrClient = IsServer ? "Server" : "Client";
        Debug.Log($"{serverOrClient} received LoadEventCompleted event via OnLoadEventCompleted notification");
    }
}

If you think that you are registering for both OnSceneEvent and OnLoadEventCompleted on the server and client side, then perhaps you could provide me with the script files that are registering for those events?

[Dockyardb]

Hello @NoelStephensUnity ,
NetworkSceneManager.OnSceneEvent was just a test if it happens with this event aswell but yes it is only the server that registers to this event.
NetworkSceneManager.OnLoadEventCompleted Only the Host/server registers to this event no client.

And i also read the documentation before i opened this ticket. Furthermore i wrote with some ppl on the dedicated netcode.gameobjects discord and they could repoduce the same issue.

I don't really much from my code but sure here:

        public void Host(ConnectionPayload payload)
        {
            connectionPayload = payload;

            NetworkManager.Singleton.ConnectionApprovalCallback += ApprovalCheck;

            NetworkManager.Singleton.StartHost();
            NetworkManager.Singleton.SceneManager.OnLoadEventCompleted += GameManager.Instance.OnSceneLoaded;

            NetworkSceneChange(SceneNames.LOBBY);
        }

Also as i wrote the error only occures when there is no other connection. If there is another client connected it gets called only once on the server.

If i can help you more please let me know.

[NoelStephensUnity]

@Dockyardb thank you for this clarification! It helped me narrow down what could be happening.
Let me setup a test and check this real quick. I want to check this in server mode vs host mode.
If it only happens when running in host mode then I am thinking the message is being sent and processed to the "host client" so the "server" receives the notification when the SceneEventProgress completes and the "host-client" receives the notification from the message sent (which basically is processed immediately on the host).
Verifying if this is the issue you are experiencing.

[NoelStephensUnity]

@Dockyardb
That is indeed what is happening! 👍
Nice catch! 💯
I will look into why it only happens when there are no clients connected.
Followup:
A PR to resolve this is on its way!