A client can easily overwhelm the servers memory by constantly sending to a broadcast hub method

[BrennanConroy]

We currently fire-and-forget hub invocations

SignalR/src/Microsoft.AspNetCore.SignalR.Core/HubConnectionHandler.cs

Line 187 in 9a0c190

_ = _dispatcher.DispatchMessageAsync(connection, message);

This can cause high lock contention and quickly grow the servers memory when many invocations are trying to write to the same connection. A quick test where we await the invocations shows stable low memory without affecting RPS in the load test that found this.

Server Hub

public class BroadcastHub : Hub
{
    public Task Broadcast(string message)
    {
        return Clients.All.SendAsync(message);
    }
}

Client

while (true)
{
    hubConnection.SendAsync("Broadcast", "flood server");
}

[muratg]

Approved.