Can't get RunTransaction with Firebase in Unity to work - unity3d

Question

I'm working on a game in Unity, using Firebase for user and game data.
Everything is fine saving the game to Unity, but in Multiplayer I have the challenge to pair an open game to a unique player 2.
The flow is:
1. You look for a game with a state of "open"
2. If no game is found within X seconds, a new one is created with the state of "open"
I have a query that returns open games (those with state "open")
This query is added a Firebase eventhandler
public void OnButtonLookForOpenMPGames()
{
this.OpenFirebaseGamesAsHost = this.LiveGamereference.OrderByChild("State").EqualTo(WYMSettings.MP_GAME_STATE_OPEN_TO_PLAYER2)
.LimitToFirst(3);
this.OpenFirebaseGamesAsHost.ChildAdded += this.OnOpenMPGameFound;
}
This fires fine in the handler:
private void OnOpenMPGameFound(object sender, ChildChangedEventArgs args)
{
Debug.Log("Looking for open games");
if (args.DatabaseError != null)
{
// handle errors
}
else
{
Debug.Log("Open game found (it may be my own)");
// remove event listener because we got a hit
// it will fire as many times as it's true!
this.OpenFirebaseGamesAsHost.ChildAdded -= this.OnOpenMPGameFound;
if (args.Snapshot.Child("HostId").Value.ToString() != FirebaseAuth.DefaultInstance.CurrentUser.UserId)
{
Debug.Log("Other game than mine found open");
// this.AddDelayedUpdateAction(() =>
// {
// this.MPGameLockInTransaction(args.Snapshot.Reference);
// });
this.MPGameLockInTransaction(args.Snapshot.Reference);
}
}
}
The problem: The handler passes this on to the transaction function, but it fails with an inner exception (Internal Task Faulted) - I've tried many different variations, but can't figure this one out from the official Firebase example.
Problem code:
What I want to achieve is to lock only that game to those two players, the host and the players 2 in this example querying for open games. The State is an int, but here a string for clarity.
private void MPGameLockInTransaction(DatabaseReference mpreference)
{
mpreference.RunTransaction(mutableData =>
{
MultiPlayerGame transactionMPG = mutableData.Value as MultiPlayerGame;
if (transactionMPG == null)
{
return TransactionResult.Abort();
}
if (transactionMPG.State != "open")
{
// game is taken, abort
Debug.Log("transaction aborted");
return TransactionResult.Abort();
}
transactionMPG.State = "game started";
mutableData.Value = transactionMPG;
return TransactionResult.Success(mutableData);
}).ContinueWith(task =>
{
if (task.Exception != null)
{
Debug.Log("Transactionlock to game failed" + task.Exception.ToString());
// Look over again
// not implemented yet
}
else
{
Debug.Log("starting game immediately");
this.AddDelayedUpdateAction(() => this.StartMPGameImmediatelyFromSearch());
}
});
}

Answer 1

This is just a guess but it might be related to threading.
In newer .Net version ContinueWith might end on a thread where most of the Unity API may not be called (including Debug.Log).
Instead you could try and use ContinueWithOnMainThread from the extensions instead which was created exactly for this reason.
With the .NET 4.x runtime, continuations may often execute in the background, whilst this extension method pushes them onto the main thread.
The .NET 3.x runtime didn't have this issue as continuations were contained within the Parse library, which did this implicitly.