use immutable queue as mutable one seems to have threading issues on …

…native?

Modules/Replication/shared/src/main/scala/replication/DeltaDissemination.scala

@@ -11,6 +11,7 @@ import replication.JsoniterCodecs.given
 import replication.ProtocolMessage.*
 
 import scala.annotation.targetName
+import scala.collection.immutable.Queue
 import scala.collection.mutable
 import scala.concurrent.ExecutionContext
 import scala.util.{Failure, Success, Try}
@@ -22,7 +23,7 @@ trait Aead {
 
 object DeltaDissemination {
   val executeImmediately = new ExecutionContext {
-    override def execute(runnable: Runnable): Unit = runnable.run()
+    override def execute(runnable: Runnable): Unit     = runnable.run()
     override def reportFailure(cause: Throwable): Unit = throw cause
   }
 }
@@ -117,16 +118,16 @@ class DeltaDissemination[State](
   }
 
   // note that deltas are not guaranteed to be ordered the same in the buffers
-  val lock: AnyRef                                                       = new {}
-  private val pastPayloads: mutable.Queue[CachedMessage[Payload[State]]] = mutable.Queue.empty
+  val lock: AnyRef                                               = new {}
+  private var pastPayloads: Queue[CachedMessage[Payload[State]]] = Queue.empty
 
   val keepPastPayloads = 100
 
   def allPayloads: List[CachedMessage[Payload[State]]] = lock.synchronized(pastPayloads.toList)
   private def rememberPayload(payload: CachedMessage[Payload[State]]): Unit = lock.synchronized {
-    pastPayloads.enqueue(payload)
+    pastPayloads = pastPayloads.enqueue(payload)
     if pastPayloads.sizeIs > keepPastPayloads then
-      pastPayloads.dequeue()
+      pastPayloads = pastPayloads.drop(1)
       ()
   }