Simplify attachment of the token

Author: sakno

src/DotNext.Threading/Threading/LinkedCancellationTokenSource.cs

@@ -13,12 +13,14 @@ namespace DotNext.Threading;
 /// </remarks>
 public abstract class LinkedCancellationTokenSource : CancellationTokenSource
 {
-    private protected static readonly Action<object?, CancellationToken> CancellationCallback;
+    private Atomic.Boolean status;
 
-    static LinkedCancellationTokenSource()
+    private protected LinkedCancellationTokenSource() => CancellationOrigin = Token;
+    
+    private protected CancellationTokenRegistration Attach(CancellationToken token)
     {
-        CancellationCallback = OnCanceled;
-
+        return token.UnsafeRegister(OnCanceled, this);
+        
         static void OnCanceled(object? source, CancellationToken token)
         {
             Debug.Assert(source is LinkedCancellationTokenSource);
@@ -27,10 +29,6 @@ static void OnCanceled(object? source, CancellationToken token)
         }
     }
 
-    private Atomic.Boolean status;
-
-    private protected LinkedCancellationTokenSource() => CancellationOrigin = Token;
-
     private void Cancel(CancellationToken token)
     {
         if (status.FalseToTrue())

src/DotNext.Threading/Threading/LinkedTokenSourceFactory.cs

@@ -141,8 +141,8 @@ internal Linked2CancellationTokenSource(in CancellationToken token1, in Cancella
             Debug.Assert(token1.CanBeCanceled);
             Debug.Assert(token2.CanBeCanceled);
 
-            registration1 = token1.UnsafeRegister(CancellationCallback, this);
-            registration2 = token2.UnsafeRegister(CancellationCallback, this);
+            registration1 = Attach(token1);
+            registration2 = Attach(token2);
         }
 
         protected override void Dispose(bool disposing)
@@ -172,13 +172,13 @@ internal MultipleLinkedCancellationTokenSource(ReadOnlySpan<CancellationToken> t
                 {
                     if (token != first && token.CanBeCanceled)
                     {
-                        writer.Add(token.UnsafeRegister(CancellationCallback, this));
+                        writer.Add(Attach(token));
                     }
                 }
 
                 if (first.CanBeCanceled && writer.WrittenCount > 0)
                 {
-                    writer.Add(first.UnsafeRegister(CancellationCallback, this));
+                    writer.Add(Attach(first));
                 }
 
                 registrations = writer.DetachOrCopyBuffer();