don't use unsafe to update nextName (#1892)

* don't use unsafe to update nextName

* Update Children.scala

* Update Children.scala

* use varhandle

* Update AbstractActorCell.java

* review comment

* Update Children.scala

Author: pjfanning

actor/src/main/java/org/apache/pekko/actor/dungeon/AbstractActorCell.java

@@ -13,13 +13,16 @@
 
 package org.apache.pekko.actor.dungeon;
 
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+
 import org.apache.pekko.actor.ActorCell;
 import org.apache.pekko.util.Unsafe;
 
 final class AbstractActorCell {
   static final long mailboxOffset;
   static final long childrenOffset;
-  static final long nextNameOffset;
+  static final VarHandle nextNameHandle;
   static final long functionRefsOffset;
 
   static {
@@ -32,14 +35,17 @@ final class AbstractActorCell {
           Unsafe.instance.objectFieldOffset(
               ActorCell.class.getDeclaredField(
                   "org$apache$pekko$actor$dungeon$Children$$_childrenRefsDoNotCallMeDirectly"));
-      nextNameOffset =
-          Unsafe.instance.objectFieldOffset(
-              ActorCell.class.getDeclaredField(
-                  "org$apache$pekko$actor$dungeon$Children$$_nextNameDoNotCallMeDirectly"));
       functionRefsOffset =
           Unsafe.instance.objectFieldOffset(
               ActorCell.class.getDeclaredField(
                   "org$apache$pekko$actor$dungeon$Children$$_functionRefsDoNotCallMeDirectly"));
+      MethodHandles.Lookup lookup =
+          MethodHandles.privateLookupIn(ActorCell.class, MethodHandles.lookup());
+      nextNameHandle =
+          lookup.findVarHandle(
+              ActorCell.class,
+              "org$apache$pekko$actor$dungeon$Children$$_nextNameDoNotCallMeDirectly",
+              long.class);
     } catch (Throwable t) {
       throw new ExceptionInInitializerError(t);
     }

actor/src/main/scala/org/apache/pekko/actor/dungeon/Children.scala

@@ -122,11 +122,11 @@ private[pekko] trait Children { this: ActorCell =>
 
   @nowarn @volatile private var _nextNameDoNotCallMeDirectly = 0L
   final protected def randomName(sb: java.lang.StringBuilder): String = {
-    val num = Unsafe.instance.getAndAddLong(this, AbstractActorCell.nextNameOffset, 1): @nowarn("cat=deprecation")
+    val num: Long = AbstractActorCell.nextNameHandle.getAndAdd(this, 1L)
     Helpers.base64(num, sb)
   }
   final protected def randomName(): String = {
-    val num = Unsafe.instance.getAndAddLong(this, AbstractActorCell.nextNameOffset, 1): @nowarn("cat=deprecation")
+    val num: Long = AbstractActorCell.nextNameHandle.getAndAdd(this, 1L)
     Helpers.base64(num)
   }