8250240: Address use of default constructors in the java.util.concurrent

Reviewed-by: martin, lancea

src/java.base/share/classes/java/util/concurrent/AbstractExecutorService.java

@@ -76,6 +76,11 @@ import java.util.List;
  */
 public abstract class AbstractExecutorService implements ExecutorService {
 
+    /**
+     * Constructor for subclasses to call.
+     */
+    public AbstractExecutorService() {}
+
     /**
      * Returns a {@code RunnableFuture} for the given runnable and default
      * value.

src/java.base/share/classes/java/util/concurrent/ForkJoinTask.java

@@ -242,6 +242,11 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
     private static final int SIGNAL   = 1 << 16; // true if joiner waiting
     private static final int SMASK    = 0xffff;  // short bits for tags
 
+    /**
+     * Constructor for subclasses to call.
+     */
+    public ForkJoinTask() {}
+
     static boolean isExceptionalStatus(int s) {  // needed by subclasses
         return (s & THROWN) != 0;
     }

src/java.base/share/classes/java/util/concurrent/RecursiveAction.java

@@ -165,6 +165,11 @@ package java.util.concurrent;
 public abstract class RecursiveAction extends ForkJoinTask<Void> {
     private static final long serialVersionUID = 5232453952276485070L;
 
+    /**
+     * Constructor for subclasses to call.
+     */
+    public RecursiveAction() {}
+
     /**
      * The main computation performed by this task.
      */

src/java.base/share/classes/java/util/concurrent/RecursiveTask.java

@@ -68,6 +68,11 @@ package java.util.concurrent;
 public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
     private static final long serialVersionUID = 5232453952276485270L;
 
+    /**
+     * Constructor for subclasses to call.
+     */
+    public RecursiveTask() {}
+
     /**
      * The result of the computation.
      */

src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java

@@ -65,6 +65,11 @@ public abstract class AbstractQueuedLongSynchronizer
 
     private static final long serialVersionUID = 7373984972572414692L;
 
+    /**
+     * Constructor for subclasses to call.
+     */
+    public AbstractQueuedLongSynchronizer() {}
+
     /*
      * To keep sources in sync, the remainder of this source file is
      * exactly cloned from AbstractQueuedSynchronizer, replacing class