8306785: fix deficient spliterators for Sequenced Collections

Reviewed-by: rriggs
Backport-of: 743e8b8e0a9fe032a0dd652a4fef1f761af66595

Author: Stuart Marks

src/java.base/share/classes/java/util/ArrayList.java

@@ -1509,7 +1509,10 @@ private void updateSizeAndModCount(int sizeChange) {
         public Spliterator<E> spliterator() {
             checkForComodification();
 
-            // ArrayListSpliterator not used here due to late-binding
+            // This Spliterator needs to late-bind to the subList, not the outer
+            // ArrayList. Note that it is legal for structural changes to be made
+            // to a subList after spliterator() is called but before any spliterator
+            // operations that would causing binding are performed.
             return new Spliterator<E>() {
                 private int index = offset; // current index, modified on advance/split
                 private int fence = -1; // -1 until used; then one past last index
@@ -1628,9 +1631,7 @@ final class ArrayListSpliterator implements Spliterator<E> {
          * be worthwhile in practice. To carry this out, we (1) lazily
          * initialize fence and expectedModCount until the latest
          * point that we need to commit to the state we are checking
-         * against; thus improving precision.  (This doesn't apply to
-         * SubLists, that create spliterators with current non-lazy
-         * values).  (2) We perform only a single
+         * against; thus improving precision. (2) We perform only a single
          * ConcurrentModificationException check at the end of forEach
          * (the most performance-sensitive method). When using forEach
          * (as opposed to iterators), we can normally only detect

src/java.base/share/classes/java/util/ReverseOrderDequeView.java

@@ -61,7 +61,7 @@ public Iterator<E> iterator() {
     }
 
     public Spliterator<E> spliterator() {
-        return Spliterators.spliteratorUnknownSize(base.descendingIterator(), 0);
+        return Spliterators.spliterator(this, Spliterator.ORDERED);
     }
 
     // ========== Collection ==========

src/java.base/share/classes/java/util/ReverseOrderListView.java

@@ -151,8 +151,7 @@ public Iterator<E> iterator() {
     }
 
     public Spliterator<E> spliterator() {
-        // TODO can probably improve this
-        return Spliterators.spliteratorUnknownSize(new DescendingIterator(), 0);
+        return Spliterators.spliterator(this, Spliterator.ORDERED);
     }
 
     // ========== Collection ==========

src/java.base/share/classes/java/util/ReverseOrderSortedSetView.java

@@ -111,7 +111,7 @@ public Iterator<E> iterator() {
     }
 
     public Spliterator<E> spliterator() {
-        return Spliterators.spliteratorUnknownSize(descendingIterator(base), 0);
+        return Spliterators.spliterator(this, Spliterator.ORDERED);
     }
 
     // ========== Collection ==========

src/java.base/share/classes/java/util/Spliterators.java

@@ -948,10 +948,12 @@ static final class ArraySpliterator<T> implements Spliterator<T> {
         private int index;        // current index, modified on advance/split
         private final int fence;  // one past last index
         private final int characteristics;
-        private long estimatedSize; // estimated size, to help to split evenly
+        private long estimatedSize; // if >= 0, the estimated size, to help to split evenly
+                                    // if -1, exact size is known to be fence - index
 
         /**
          * Creates a spliterator covering all of the given array.
+         * Its size is known exactly and it is SIZED and SUBSIZED.
          * @param array the array, assumed to be unmodified during use
          * @param additionalCharacteristics Additional spliterator characteristics
          * of this spliterator's source or elements beyond {@code SIZED} and
@@ -962,7 +964,8 @@ public ArraySpliterator(Object[] array, int additionalCharacteristics) {
         }
 
         /**
-         * Creates a spliterator covering the given array and range
+         * Creates a spliterator covering the given array and range.
+         * Its size is known exactly and it is SIZED and SUBSIZED.
          * @param array the array, assumed to be unmodified during use
          * @param origin the least index (inclusive) to cover
          * @param fence one past the greatest index to cover
@@ -978,6 +981,18 @@ public ArraySpliterator(Object[] array, int origin, int fence, int additionalCha
             this.estimatedSize = -1;
         }
 
+        /**
+         * Creates a spliterator covering the given array and range but that is
+         * not SIZED or SUBSIZED. This case occurs as a result of splitting another
+         * spliterator that is not sized, so it's inappropriate for one of its
+         * sub-spliterators to be sized.
+         * @param array the array, assumed to be unmodified during use
+         * @param origin the least index (inclusive) to cover
+         * @param fence one past the greatest index to cover
+         * @param characteristics characteristics of this spliterator's source; {@code SIZED} and
+         *        {@code SUBSIZED} are removed if present
+         * @param estimatedSize the size estimate; should always be nonnegative
+         */
         private ArraySpliterator(Object[] array, int origin, int fence, int characteristics, long estimatedSize) {
             this.array = array;
             this.index = origin;

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

@@ -1822,8 +1822,7 @@ public Iterator<E> iterator() {
         }
 
         public Spliterator<E> spliterator() {
-            // TODO can probably improve this
-            return Spliterators.spliteratorUnknownSize(new DescendingIterator(), 0);
+            return Spliterators.spliterator(this, Spliterator.ORDERED);
         }
 
         // ========== Collection ==========