Skip unnecessary lookup in EventRegistrationTokenTable<T> (#1440)

src/cswinrt/strings/WinRT.cs

@@ -1066,11 +1066,21 @@ private EventRegistrationToken AddEventHandlerNoLock(T handler)
  // Get a registration token, making sure that we haven't already used the value. This should be quite
  // rare, but in the case it does happen, just keep trying until we find one that's unused.
  EventRegistrationToken token = GetPreferredToken(handler);
+
+#if NET6_0_OR_GREATER
+ // When on .NET 6+, just iterate on TryAdd, which allows skipping the extra
+ // lookup on the last iteration (as the handler is added rigth away instead).
+ while (!m_tokens.TryAdd(token, handler))
+ {
+ token = new EventRegistrationToken { Value = token.Value + 1 };
+ }
+#else
  while (m_tokens.ContainsKey(token))
  {
  token = new EventRegistrationToken { Value = token.Value + 1 };
  }
  m_tokens[token] = handler;
+#endif
 
  return token;
  }