8022724: lint warnings in j.u.concurrent packages

Reviewed-by: chegar, lancea, darcy

src/share/classes/java/util/concurrent/CompletableFuture.java

@@ -420,6 +420,7 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
     }
 
     /** Base class can act as either FJ or plain Runnable */
+    @SuppressWarnings("serial")
     abstract static class Async extends ForkJoinTask<Void>
         implements Runnable, AsynchronousCompletionTask {
         public final Void getRawResult() { return null; }
@@ -671,6 +672,7 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
     }
 
     // Opportunistically subclass AtomicInteger to use compareAndSet to claim.
+    @SuppressWarnings("serial")
     abstract static class Completion extends AtomicInteger implements Runnable {
     }
 

src/share/classes/java/util/concurrent/ConcurrentHashMap.java

@@ -4716,6 +4716,7 @@ public class ConcurrentHashMap<K,V> extends AbstractMap<K,V>
      * Base class for bulk tasks. Repeats some fields and code from
      * class Traverser, because we need to subclass CountedCompleter.
      */
+    @SuppressWarnings("serial")
     abstract static class BulkTask<K,V,R> extends CountedCompleter<R> {
         Node<K,V>[] tab;        // same as Traverser
         Node<K,V> next;

src/share/classes/java/util/concurrent/atomic/Striped64.java

@@ -43,6 +43,7 @@ import java.util.concurrent.ThreadLocalRandom;
  * for classes supporting dynamic striping on 64bit values. The class
  * extends Number so that concrete subclasses must publicly do so.
  */
+@SuppressWarnings("serial")
 abstract class Striped64 extends Number {
     /*
      * This class maintains a lazily-initialized table of atomically