8186265: Make toString() methods of "task" objects more useful

Reviewed-by: martin, psandoz, rriggs, dholmes, darcy

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

@@ -2490,13 +2490,13 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
         for (Completion p = stack; p != null; p = p.next)
             ++count;
         return super.toString() +
-            ((r == null) ?
-             ((count == 0) ?
-              "[Not completed]" :
-              "[Not completed, " + count + " dependents]") :
-             (((r instanceof AltResult) && ((AltResult)r).ex != null) ?
-              "[Completed exceptionally]" :
-              "[Completed normally]"));
+            ((r == null)
+             ? ((count == 0)
+                ? "[Not completed]"
+                : "[Not completed, " + count + " dependents]")
+             : (((r instanceof AltResult) && ((AltResult)r).ex != null)
+                ? "[Completed exceptionally: " + ((AltResult)r).ex + "]"
+                : "[Completed normally]"));
     }
 
     // jdk9 additions

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

@@ -514,6 +514,9 @@ public class Executors {
             task.run();
             return result;
         }
+        public String toString() {
+            return super.toString() + "[Wrapped task = " + task + "]";
+        }
     }
 
     /**
@@ -540,6 +543,10 @@ public class Executors {
                 throw e.getException();
             }
         }
+
+        public String toString() {
+            return super.toString() + "[Wrapped task = " + task + "]";
+        }
     }
 
     /**
@@ -592,6 +599,10 @@ public class Executors {
                 throw e.getException();
             }
         }
+
+        public String toString() {
+            return super.toString() + "[Wrapped task = " + task + "]";
+        }
     }
 
     /**

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

@@ -1375,6 +1375,9 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         public final void setRawResult(T v) { result = v; }
         public final boolean exec() { runnable.run(); return true; }
         public final void run() { invoke(); }
+        public String toString() {
+            return super.toString() + "[Wrapped task = " + runnable + "]";
+        }
         private static final long serialVersionUID = 5232453952276885070L;
     }
 
@@ -1392,6 +1395,9 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         public final void setRawResult(Void v) { }
         public final boolean exec() { runnable.run(); return true; }
         public final void run() { invoke(); }
+        public String toString() {
+            return super.toString() + "[Wrapped task = " + runnable + "]";
+        }
         private static final long serialVersionUID = 5232453952276885070L;
     }
 
@@ -1437,6 +1443,9 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
             }
         }
         public final void run() { invoke(); }
+        public String toString() {
+            return super.toString() + "[Wrapped task = " + callable + "]";
+        }
         private static final long serialVersionUID = 2838392045355241008L;
     }
 

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

@@ -480,6 +480,41 @@ public class FutureTask<V> implements RunnableFuture<V> {
         }
     }
 
+    /**
+     * Returns a string representation of this FutureTask.
+     *
+     * @implSpec
+     * The default implementation returns a string identifying this
+     * FutureTask, as well as its completion state.  The state, in
+     * brackets, contains one of the strings {@code "Completed Normally"},
+     * {@code "Completed Exceptionally"}, {@code "Cancelled"}, or {@code
+     * "Not completed"}.
+     *
+     * @return a string representation of this FutureTask
+     */
+    public String toString() {
+        final String status;
+        switch (state) {
+        case NORMAL:
+            status = "[Completed normally]";
+            break;
+        case EXCEPTIONAL:
+            status = "[Completed exceptionally: " + outcome + "]";
+            break;
+        case CANCELLED:
+        case INTERRUPTING:
+        case INTERRUPTED:
+            status = "[Cancelled]";
+            break;
+        default:
+            final Callable<?> callable = this.callable;
+            status = (callable == null)
+                ? "[Not completed]"
+                : "[Not completed, task = " + callable + "]";
+        }
+        return super.toString() + status;
+    }
+
     // VarHandle mechanics
     private static final VarHandle STATE;
     private static final VarHandle RUNNER;