=clt #18232 Serializer for ClusterSingleton

akka-cluster-tools/src/main/scala/akka/cluster/singleton/ClusterSingletonManager.scala

@@ -111,6 +111,11 @@ final class ClusterSingletonManagerSettings(
     new ClusterSingletonManagerSettings(singletonName, role, removalMargin, handOverRetryInterval)
 }
 
+/**
+ * Marker trait for remote messages with special serializer.
+ */
+sealed trait ClusterSingletonMessage extends Serializable
+
 object ClusterSingletonManager {
 
   /**
@@ -136,25 +141,25 @@ object ClusterSingletonManager {
   /**
    * INTERNAL API
    */
-  private object Internal {
+  private[akka] object Internal {
     /**
      * Sent from new oldest to previous oldest to initiate the
      * hand-over process. `HandOverInProgress` and `HandOverDone`
      * are expected replies.
      */
-    case object HandOverToMe
+    case object HandOverToMe extends ClusterSingletonMessage
     /**
      * Confirmation by the previous oldest that the hand
      * over process, shut down of the singleton actor, has
      * started.
      */
-    case object HandOverInProgress
+    case object HandOverInProgress extends ClusterSingletonMessage
     /**
      * Confirmation by the previous oldest that the singleton
      * actor has been terminated and the hand-over process is
      * completed.
      */
-    case object HandOverDone
+    case object HandOverDone extends ClusterSingletonMessage
     /**
      * Sent from from previous oldest to new oldest to
      * initiate the normal hand-over process.
@@ -162,7 +167,7 @@ object ClusterSingletonManager {
      * oldest immediately, without knowing who was previous
      * oldest.
      */
-    case object TakeOverFromMe
+    case object TakeOverFromMe extends ClusterSingletonMessage
 
     final case class HandOverRetry(count: Int)
     final case class TakeOverRetry(count: Int)