Remove the CancellationTokenSource.Dispose() call inside of the Actor…

…ContextExtras.Dispose(). (#1920)

It should fix the CancellationTokenDisposed exception issue #1916

src/Proto.Actor/Context/ActorContextExtras.cs

@@ -1,4 +1,4 @@
-// -----------------------------------------------------------------------
+// -----------------------------------------------------------------------
 // <copyright file="ActorContextExtras.cs" company="Asynkron AB">
 // Copyright (C) 2015-2022 Asynkron AB All rights reserved
 // </copyright>
@@ -37,7 +37,14 @@ public ActorContextExtras(IContext context)
  public void Dispose()
  {
  ReceiveTimeoutTimer?.Dispose();
- CancellationTokenSource.Dispose();
+ ReceiveTimeoutTimer = null;
+
+ // NOTE: We don't dispose CancellationTokenSource here on purpose, doing so causes
+ // ActorSystem shutdown issues because of DefaultMailbox.PostSystemMessage doing
+ // a Cancel call on that CancellationTokenSource. This can occur in cases of stopping
+ // an actor twice. Given that we utilize this CancellationTokenSource only via the Cancel()
+ // call, doing a Dispose() call is not required. More info can be found here:
+ // https://github.com/asynkron/protoactor-dotnet/issues/1916
  }
 
  public void InitReceiveTimeoutTimer(Timer timer) => ReceiveTimeoutTimer = timer;