Summary

Replace default constructors in java.util.concurrent with equivalent explicit constructors.

Problem

Default constructors considered harmful in formal APIs.

Solution

Add explicit constructors.

Specification

diff -r d62da6fc4074 src/java.base/share/classes/java/util/concurrent/AbstractExecutorService.java
--- a/src/java.base/share/classes/java/util/concurrent/AbstractExecutorService.java	Thu Jul 23 20:25:41 2020 +0100
+++ b/src/java.base/share/classes/java/util/concurrent/AbstractExecutorService.java	Thu Jul 23 14:59:38 2020 -0700
@@ -77,6 +77,11 @@
 public abstract class AbstractExecutorService implements ExecutorService {
 
     /**
+     * Constructor for subclasses to call.
+     */
+    public AbstractExecutorService() {}
+
+    /**
      * Returns a {@code RunnableFuture} for the given runnable and default
      * value.
      *
diff -r d62da6fc4074 src/java.base/share/classes/java/util/concurrent/ForkJoinTask.java
--- a/src/java.base/share/classes/java/util/concurrent/ForkJoinTask.java	Thu Jul 23 20:25:41 2020 +0100
+++ b/src/java.base/share/classes/java/util/concurrent/ForkJoinTask.java	Thu Jul 23 14:59:38 2020 -0700
@@ -242,6 +242,11 @@
     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;
     }
diff -r d62da6fc4074 src/java.base/share/classes/java/util/concurrent/RecursiveAction.java
--- a/src/java.base/share/classes/java/util/concurrent/RecursiveAction.java	Thu Jul 23 20:25:41 2020 +0100
+++ b/src/java.base/share/classes/java/util/concurrent/RecursiveAction.java	Thu Jul 23 14:59:38 2020 -0700
@@ -166,6 +166,11 @@
     private static final long serialVersionUID = 5232453952276485070L;
 
     /**
+     * Constructor for subclasses to call.
+     */
+    public RecursiveAction() {}
+
+    /**
      * The main computation performed by this task.
      */
     protected abstract void compute();
diff -r d62da6fc4074 src/java.base/share/classes/java/util/concurrent/RecursiveTask.java
--- a/src/java.base/share/classes/java/util/concurrent/RecursiveTask.java	Thu Jul 23 20:25:41 2020 +0100
+++ b/src/java.base/share/classes/java/util/concurrent/RecursiveTask.java	Thu Jul 23 14:59:38 2020 -0700
@@ -69,6 +69,11 @@
     private static final long serialVersionUID = 5232453952276485270L;
 
     /**
+     * Constructor for subclasses to call.
+     */
+    public RecursiveTask() {}
+
+    /**
      * The result of the computation.
      */
     @SuppressWarnings("serial") // Conditionally serializable
diff -r d62da6fc4074 src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java
--- a/src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java	Thu Jul 23 20:25:41 2020 +0100
+++ b/src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java	Thu Jul 23 14:59:38 2020 -0700
@@ -65,6 +65,11 @@
 
     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