playerConnecting event crashes when performing async database queries in C#

[woozievert]

What happened?

When performing async database queries (such as Entity Framework Core or similar ORM operations) inside the playerConnecting event handler, the server crashes or throws exceptions, even when using deferrals.defer() and [FromSource] correctly.
The code is structured according to the official documentation:
`
private async void OnPlayerConnecting(
[FromSource] Player player, string playerName,
dynamic setKickReason, dynamic deferrals)
{
deferrals.defer();

try
{
    // This causes crashes/exceptions
    var ban = await BanRepo.FindActiveBanAsync(license, ip);
    
    if (ban != null)
    {
        deferrals.done($"You are banned. Reason: {ban.Reason}");
        return;
    }
    
    deferrals.done();
}
catch (Exception ex)
{
    Logger.Error("Ban check failed", ex);
    deferrals.done("Server error");
}

}
`
The database query (FindActiveBanAsync) performs a typical async operation (e.g., DbContext.Bans.Where(...).FirstOrDefaultAsync()), but this causes the server to crash or become unstable.

Expected result

According to the official playerConnecting documentation, after calling deferrals.defer(), it should be safe to perform async operations: > "Assuming you have a function called IsBanned of type Task - normally you'd do a database query here, which might take some time" The documentation example shows: if (await IsBanned(licenseIdentifier)){ deferrals.done($"You have been kicked...");} This suggests async database queries should work, but in practice they cause crashes.

Reproduction steps

1. Create a server-side C# resource with Entity Framework Core or any async database library

2. Set up a repository method that performs an async database query:
   public async Task<BanData> FindActiveBanAsync(string license, string ip) { return await _dbContext.Bans .Where(b => (b.License == license || b.IpAddress == ip) && (!b.ExpiresAt.HasValue || b.ExpiresAt.Value > DateTime.UtcNow)) .FirstOrDefaultAsync(); }

3. Call this method in the playerConnecting handler:
   `private async void OnPlayerConnecting(
   [FromSource] Player player, string playerName,
   dynamic setKickReason, dynamic deferrals)
   {
   deferrals.defer();

   string license = player.Identifiers.FirstOrDefault(id => id.StartsWith("license:"));

   deferrals.update("Checking ban status...");

   var ban = await BanRepo.FindActiveBanAsync(license, null);

   if (ban != null)
   {
   deferrals.done($"Banned: {ban.Reason}");
   return;
   }

   deferrals.done();
   }`

4. Start the server and attempt to connect

5. Server crashes or throws exceptions during the database query

Importancy

There's a workaround

Area(s)

FiveM, ScRT: C#

Specific version(s)

FiveM 25963

Additional information

No response

[Legacy-TacticalGamingInteractive]

Can confirm

[lLukDreams]

Use await Delay(0); before eevery deferral event and report back if it still crashes

PS: Every native needs to be exectued in main thread, using wait Delay makes sure of it, deferral is an example of needing be executed in MT, a big flaw for the C# runtime but we hope for something better with .net core runtime :)

[woozievert]

Use await Delay(0); before eevery deferral event and report back if it still crashes

PS: Every native needs to be exectued in main thread, using wait Delay makes sure of it, deferral is an example of needing be executed in MT, a big flaw for the C# runtime but we hope for something better with .net core runtime :)

Not works

[lLukDreams]

i can assure you, that async calls are more than possible in playerconnecting, the issue is not coming from that, add a try catch and some logging to see where you get, like i said, the c# runtime is really fragile to exceptions and not running in mainthread for specific api calls

[woozievert]

i can assure you, that async calls are more than possible in playerconnecting, the issue is not coming from that, add a try catch and some logging to see where you get, like i said, the c# runtime is really fragile to exceptions and not running in mainthread for specific api calls

A try-catch won't help here. The server main thread (svMain) hangs entirely before any exception is thrown. It's a hard freeze, not a catchable error.

[AvarianKnight]

Does this still happen if you await Delay(0) after your var ban = await BanRepo.FindActiveBanAsync(license, null); call?

[woozievert]

Does this still happen if you await Delay(0) after your var ban = await BanRepo.FindActiveBanAsync(license, null); call?

it works

[woozievert]

Does this still happen if you await Delay(0) after your var ban = await BanRepo.FindActiveBanAsync(license, null); call?

after await switchToMainThread?

[AvarianKnight]

Whenever you await Delay(0); you marshal back into the game loop or in this case the svMain loop.

This is a big footgun since C# can do concurrency, but it's expected you call everything on the main thread.