fix subs

Plugins/BTCPayServer.Plugins.Subscriptions/AsyncExtensions.cs

@@ -0,0 +1,57 @@
+using System;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using System.Threading;
+
+namespace BTCPayServer.Plugins.Subscriptions;
+
+public static class AsyncExtensions
+{
+    /// <summary>
+    /// Allows a cancellation token to be awaited.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public static CancellationTokenAwaiter GetAwaiter(this CancellationToken ct)
+    {
+        // return our special awaiter
+        return new CancellationTokenAwaiter
+        {
+            CancellationToken = ct
+        };
+    }
+
+    /// <summary>
+    /// The awaiter for cancellation tokens.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public struct CancellationTokenAwaiter : INotifyCompletion, ICriticalNotifyCompletion
+    {
+        public CancellationTokenAwaiter(CancellationToken cancellationToken)
+        {
+            CancellationToken = cancellationToken;
+        }
+
+        internal CancellationToken CancellationToken;
+
+        public object GetResult()
+        {
+            // this is called by compiler generated methods when the
+            // task has completed. Instead of returning a result, we 
+            // just throw an exception.
+            if (IsCompleted) throw new OperationCanceledException();
+            else throw new InvalidOperationException("The cancellation token has not yet been cancelled.");
+        }
+
+        // called by compiler generated/.net internals to check
+        // if the task has completed.
+        public bool IsCompleted => CancellationToken.IsCancellationRequested;
+
+        // The compiler will generate stuff that hooks in
+        // here. We hook those methods directly into the
+        // cancellation token.
+        public void OnCompleted(Action continuation) =>
+            CancellationToken.Register(continuation);
+        public void UnsafeOnCompleted(Action continuation) =>
+            CancellationToken.Register(continuation);
+    }
+}