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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.90 by jsr166, Tue Oct 25 03:13:56 2016 UTC vs.
Revision 1.123 by jsr166, Sat Nov 26 14:16:18 2016 UTC

# Line 60 | Line 60 | import java.util.function.UnaryOperator;
60   public class ArrayDeque<E> extends AbstractCollection<E>
61                             implements Deque<E>, Cloneable, Serializable
62   {
63 +    /*
64 +     * VMs excel at optimizing simple array loops where indices are
65 +     * incrementing or decrementing over a valid slice, e.g.
66 +     *
67 +     * for (int i = start; i < end; i++) ... elements[i]
68 +     *
69 +     * Because in a circular array, elements are in general stored in
70 +     * two disjoint such slices, we help the VM by writing unusual
71 +     * nested loops for all traversals over the elements.  Having only
72 +     * one hot inner loop body instead of two or three eases human
73 +     * maintenance and encourages VM loop inlining into the caller.
74 +     */
75 +
76      /**
77       * The array in which the elements of the deque are stored.
78 <     * We guarantee that all array cells not holding deque elements
79 <     * are always null.
78 >     * All array cells not holding deque elements are always null.
79 >     * The array always has at least one null slot (at tail).
80       */
81      transient Object[] elements;
82  
83      /**
84       * The index of the element at the head of the deque (which is the
85       * element that would be removed by remove() or pop()); or an
86 <     * arbitrary number 0 <= head < elements.length if the deque is empty.
86 >     * arbitrary number 0 <= head < elements.length equal to tail if
87 >     * the deque is empty.
88       */
89      transient int head;
90  
91 <    /** Number of elements in this collection. */
92 <    transient int size;
91 >    /**
92 >     * The index at which the next element would be added to the tail
93 >     * of the deque (via addLast(E), add(E), or push(E));
94 >     * elements[tail] is always null.
95 >     */
96 >    transient int tail;
97  
98      /**
99       * The maximum size of array to allocate.
# Line 92 | Line 110 | public class ArrayDeque<E> extends Abstr
110       */
111      private void grow(int needed) {
112          // overflow-conscious code
113 <        // checkInvariants();
96 <        int oldCapacity = elements.length;
113 >        final int oldCapacity = elements.length;
114          int newCapacity;
115 <        // Double size if small; else grow by 50%
115 >        // Double capacity if small; else grow by 50%
116          int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
117          if (jump < needed
118              || (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
119              newCapacity = newCapacity(needed, jump);
120          elements = Arrays.copyOf(elements, newCapacity);
121 <        if (oldCapacity - head < size) {
121 >        // Exceptionally, here tail == head needs to be disambiguated
122 >        if (tail < head || (tail == head && elements[head] != null)) {
123              // wrap around; slide first leg forward to end of array
124              int newSpace = newCapacity - oldCapacity;
125              System.arraycopy(elements, head,
# Line 115 | Line 133 | public class ArrayDeque<E> extends Abstr
133  
134      /** Capacity calculation for edge conditions, especially overflow. */
135      private int newCapacity(int needed, int jump) {
136 <        int oldCapacity = elements.length;
119 <        int minCapacity;
136 >        final int oldCapacity = elements.length, minCapacity;
137          if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
138              if (minCapacity < 0)
139                  throw new IllegalStateException("Sorry, deque too big");
# Line 137 | Line 154 | public class ArrayDeque<E> extends Abstr
154       * @since TBD
155       */
156      /* public */ void ensureCapacity(int minCapacity) {
157 <        if (minCapacity > elements.length)
158 <            grow(minCapacity - elements.length);
157 >        int needed;
158 >        if ((needed = (minCapacity + 1 - elements.length)) > 0)
159 >            grow(needed);
160          // checkInvariants();
161      }
162  
# Line 148 | Line 166 | public class ArrayDeque<E> extends Abstr
166       * @since TBD
167       */
168      /* public */ void trimToSize() {
169 <        if (size < elements.length) {
170 <            elements = toArray();
169 >        int size;
170 >        if ((size = size()) + 1 < elements.length) {
171 >            elements = toArray(new Object[size + 1]);
172              head = 0;
173 +            tail = size;
174          }
175          // checkInvariants();
176      }
# Line 170 | Line 190 | public class ArrayDeque<E> extends Abstr
190       * @param numElements lower bound on initial capacity of the deque
191       */
192      public ArrayDeque(int numElements) {
193 <        elements = new Object[numElements];
193 >        elements =
194 >            new Object[(numElements < 1) ? 1 :
195 >                       (numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
196 >                       numElements + 1];
197      }
198  
199      /**
# Line 184 | Line 207 | public class ArrayDeque<E> extends Abstr
207       * @throws NullPointerException if the specified collection is null
208       */
209      public ArrayDeque(Collection<? extends E> c) {
210 <        Object[] elements = c.toArray();
211 <        // defend against c.toArray (incorrectly) not returning Object[]
189 <        // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
190 <        size = elements.length;
191 <        if (elements.getClass() != Object[].class)
192 <            elements = Arrays.copyOf(elements, size, Object[].class);
193 <        for (Object obj : elements)
194 <            Objects.requireNonNull(obj);
195 <        this.elements = elements;
210 >        this(c.size());
211 >        addAll(c);
212      }
213  
214      /**
# Line 214 | Line 230 | public class ArrayDeque<E> extends Abstr
230      }
231  
232      /**
233 <     * Adds i and j, mod modulus.
234 <     * Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
233 >     * Circularly adds the given distance to index i, mod modulus.
234 >     * Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
235 >     * @return index 0 <= i < modulus
236       */
237 <    static final int add(int i, int j, int modulus) {
238 <        if ((i += j) - modulus >= 0) i -= modulus;
237 >    static final int add(int i, int distance, int modulus) {
238 >        if ((i += distance) - modulus >= 0) distance -= modulus;
239          return i;
240      }
241  
242      /**
243 <     * Returns the array index of the last element.
244 <     * May return invalid index -1 if there are no elements.
243 >     * Subtracts j from i, mod modulus.
244 >     * Index i must be logically ahead of index j.
245 >     * Precondition: 0 <= i < modulus, 0 <= j < modulus.
246 >     * @return the "circular distance" from j to i; corner case i == j
247 >     * is diambiguated to "empty", returning 0.
248       */
249 <    final int tail() {
250 <        return add(head, size - 1, elements.length);
249 >    static final int sub(int i, int j, int modulus) {
250 >        if ((i -= j) < 0) i += modulus;
251 >        return i;
252      }
253  
254      /**
255       * Returns element at array index i.
256 +     * This is a slight abuse of generics, accepted by javac.
257       */
258      @SuppressWarnings("unchecked")
259 <    private E elementAt(int i) {
260 <        return (E) elements[i];
259 >    static final <E> E elementAt(Object[] es, int i) {
260 >        return (E) es[i];
261      }
262  
263      /**
# Line 243 | Line 265 | public class ArrayDeque<E> extends Abstr
265       * This check doesn't catch all possible comodifications,
266       * but does catch ones that corrupt traversal.
267       */
268 <    E checkedElementAt(Object[] elements, int i) {
269 <        @SuppressWarnings("unchecked") E e = (E) elements[i];
268 >    static final <E> E nonNullElementAt(Object[] es, int i) {
269 >        @SuppressWarnings("unchecked") E e = (E) es[i];
270          if (e == null)
271              throw new ConcurrentModificationException();
272          return e;
# Line 261 | Line 283 | public class ArrayDeque<E> extends Abstr
283       * @throws NullPointerException if the specified element is null
284       */
285      public void addFirst(E e) {
286 <        // checkInvariants();
287 <        Objects.requireNonNull(e);
288 <        Object[] elements;
289 <        int capacity, h;
290 <        final int s;
269 <        if ((s = size) == (capacity = (elements = this.elements).length)) {
286 >        if (e == null)
287 >            throw new NullPointerException();
288 >        final Object[] es = elements;
289 >        es[head = dec(head, es.length)] = e;
290 >        if (head == tail)
291              grow(1);
271            capacity = (elements = this.elements).length;
272        }
273        if ((h = head - 1) < 0) h = capacity - 1;
274        elements[head = h] = e;
275        size = s + 1;
292          // checkInvariants();
293      }
294  
# Line 285 | Line 301 | public class ArrayDeque<E> extends Abstr
301       * @throws NullPointerException if the specified element is null
302       */
303      public void addLast(E e) {
304 <        // checkInvariants();
305 <        Objects.requireNonNull(e);
306 <        Object[] elements;
307 <        int capacity;
308 <        final int s;
293 <        if ((s = size) == (capacity = (elements = this.elements).length)) {
304 >        if (e == null)
305 >            throw new NullPointerException();
306 >        final Object[] es = elements;
307 >        es[tail] = e;
308 >        if (head == (tail = inc(tail, es.length)))
309              grow(1);
295            capacity = (elements = this.elements).length;
296        }
297        elements[add(head, s, capacity)] = e;
298        size = s + 1;
310          // checkInvariants();
311      }
312  
# Line 311 | Line 322 | public class ArrayDeque<E> extends Abstr
322       *         of its elements are null
323       */
324      public boolean addAll(Collection<? extends E> c) {
325 <        final int s = size, needed = c.size() - (elements.length - s);
326 <        if (needed > 0)
325 >        final int s, needed;
326 >        if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
327              grow(needed);
328 <        c.forEach((e) -> addLast(e));
328 >        c.forEach(this::addLast);
329          // checkInvariants();
330 <        return size > s;
330 >        return size() > s;
331      }
332  
333      /**
# Line 347 | Line 358 | public class ArrayDeque<E> extends Abstr
358       * @throws NoSuchElementException {@inheritDoc}
359       */
360      public E removeFirst() {
350        // checkInvariants();
361          E e = pollFirst();
362          if (e == null)
363              throw new NoSuchElementException();
364 +        // checkInvariants();
365          return e;
366      }
367  
# Line 358 | Line 369 | public class ArrayDeque<E> extends Abstr
369       * @throws NoSuchElementException {@inheritDoc}
370       */
371      public E removeLast() {
361        // checkInvariants();
372          E e = pollLast();
373          if (e == null)
374              throw new NoSuchElementException();
375 +        // checkInvariants();
376          return e;
377      }
378  
379      public E pollFirst() {
380 +        final Object[] es;
381 +        final int h;
382 +        E e = elementAt(es = elements, h = head);
383 +        if (e != null) {
384 +            es[h] = null;
385 +            head = inc(h, es.length);
386 +        }
387          // checkInvariants();
370        int s, h;
371        if ((s = size) == 0)
372            return null;
373        final Object[] elements = this.elements;
374        @SuppressWarnings("unchecked") E e = (E) elements[h = head];
375        elements[h] = null;
376        if (++h >= elements.length) h = 0;
377        head = h;
378        size = s - 1;
388          return e;
389      }
390  
391      public E pollLast() {
392 +        final Object[] es;
393 +        final int t;
394 +        E e = elementAt(es = elements, t = dec(tail, es.length));
395 +        if (e != null)
396 +            es[tail = t] = null;
397          // checkInvariants();
384        final int s, tail;
385        if ((s = size) == 0)
386            return null;
387        final Object[] elements = this.elements;
388        @SuppressWarnings("unchecked")
389        E e = (E) elements[tail = add(head, s - 1, elements.length)];
390        elements[tail] = null;
391        size = s - 1;
398          return e;
399      }
400  
# Line 396 | Line 402 | public class ArrayDeque<E> extends Abstr
402       * @throws NoSuchElementException {@inheritDoc}
403       */
404      public E getFirst() {
405 +        E e = elementAt(elements, head);
406 +        if (e == null)
407 +            throw new NoSuchElementException();
408          // checkInvariants();
409 <        if (size == 0) throw new NoSuchElementException();
401 <        return elementAt(head);
409 >        return e;
410      }
411  
412      /**
413       * @throws NoSuchElementException {@inheritDoc}
414       */
415      public E getLast() {
416 +        final Object[] es = elements;
417 +        E e = elementAt(es, dec(tail, es.length));
418 +        if (e == null)
419 +            throw new NoSuchElementException();
420          // checkInvariants();
421 <        if (size == 0) throw new NoSuchElementException();
410 <        return elementAt(tail());
421 >        return e;
422      }
423  
424      public E peekFirst() {
425          // checkInvariants();
426 <        return (size == 0) ? null : elementAt(head);
426 >        return elementAt(elements, head);
427      }
428  
429      public E peekLast() {
430          // checkInvariants();
431 <        return (size == 0) ? null : elementAt(tail());
431 >        final Object[] es;
432 >        return elementAt(es = elements, dec(tail, es.length));
433      }
434  
435      /**
# Line 434 | Line 446 | public class ArrayDeque<E> extends Abstr
446       */
447      public boolean removeFirstOccurrence(Object o) {
448          if (o != null) {
449 <            final Object[] elements = this.elements;
450 <            final int capacity = elements.length;
451 <            int from, end, to, todo;
452 <            todo = (end = (from = head) + size)
453 <                - (to = (capacity - end >= 0) ? end : capacity);
442 <            for (;; from = 0, to = todo, todo = 0) {
443 <                for (int i = from; i < to; i++)
444 <                    if (o.equals(elements[i])) {
449 >            final Object[] es = elements;
450 >            for (int i = head, end = tail, to = (i <= end) ? end : es.length;
451 >                 ; i = 0, to = end) {
452 >                for (; i < to; i++)
453 >                    if (o.equals(es[i])) {
454                          delete(i);
455                          return true;
456                      }
457 <                if (todo == 0) break;
457 >                if (to == end) break;
458              }
459          }
460          return false;
# Line 465 | Line 474 | public class ArrayDeque<E> extends Abstr
474       */
475      public boolean removeLastOccurrence(Object o) {
476          if (o != null) {
477 <            final Object[] elements = this.elements;
478 <            final int capacity = elements.length;
479 <            int from, to, end, todo;
480 <            todo = (to = ((end = (from = tail()) - size) >= -1) ? end : -1) - end;
481 <            for (;; from = capacity - 1, to = capacity - 1 - todo, todo = 0) {
473 <                for (int i = from; i > to; i--)
474 <                    if (o.equals(elements[i])) {
477 >            final Object[] es = elements;
478 >            for (int i = tail, end = head, to = (i >= end) ? end : 0;
479 >                 ; i = es.length, to = end) {
480 >                for (i--; i > to - 1; i--)
481 >                    if (o.equals(es[i])) {
482                          delete(i);
483                          return true;
484                      }
485 <                if (todo == 0) break;
485 >                if (to == end) break;
486              }
487          }
488          return false;
# Line 603 | Line 610 | public class ArrayDeque<E> extends Abstr
610       * <p>This method is called delete rather than remove to emphasize
611       * that its semantics differ from those of {@link List#remove(int)}.
612       *
613 <     * @return true if elements moved backwards
613 >     * @return true if elements near tail moved backwards
614       */
615      boolean delete(int i) {
616          // checkInvariants();
617 <        final Object[] elements = this.elements;
618 <        final int capacity = elements.length;
619 <        final int h = head;
620 <        int front;              // number of elements before to-be-deleted elt
621 <        if ((front = i - h) < 0) front += capacity;
622 <        final int back = size - front - 1; // number of elements after
617 >        final Object[] es = elements;
618 >        final int capacity = es.length;
619 >        final int h, t;
620 >        // number of elements before to-be-deleted elt
621 >        final int front = sub(i, h = head, capacity);
622 >        // number of elements after to-be-deleted elt
623 >        final int back = sub(t = tail, i, capacity) - 1;
624          if (front < back) {
625              // move front elements forwards
626              if (h <= i) {
627 <                System.arraycopy(elements, h, elements, h + 1, front);
627 >                System.arraycopy(es, h, es, h + 1, front);
628              } else { // Wrap around
629 <                System.arraycopy(elements, 0, elements, 1, i);
630 <                elements[0] = elements[capacity - 1];
631 <                System.arraycopy(elements, h, elements, h + 1, front - (i + 1));
629 >                System.arraycopy(es, 0, es, 1, i);
630 >                es[0] = es[capacity - 1];
631 >                System.arraycopy(es, h, es, h + 1, front - (i + 1));
632              }
633 <            elements[h] = null;
634 <            if ((head = (h + 1)) >= capacity) head = 0;
627 <            size--;
633 >            es[h] = null;
634 >            head = inc(h, capacity);
635              // checkInvariants();
636              return false;
637          } else {
638              // move back elements backwards
639 <            int tail = tail();
639 >            tail = dec(t, capacity);
640              if (i <= tail) {
641 <                System.arraycopy(elements, i + 1, elements, i, back);
641 >                System.arraycopy(es, i + 1, es, i, back);
642              } else { // Wrap around
643 <                int firstLeg = capacity - (i + 1);
644 <                System.arraycopy(elements, i + 1, elements, i, firstLeg);
645 <                elements[capacity - 1] = elements[0];
639 <                System.arraycopy(elements, 1, elements, 0, back - firstLeg - 1);
643 >                System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
644 >                es[capacity - 1] = es[0];
645 >                System.arraycopy(es, 1, es, 0, t - 1);
646              }
647 <            elements[tail] = null;
642 <            size--;
647 >            es[tail] = null;
648              // checkInvariants();
649              return true;
650          }
# Line 653 | Line 658 | public class ArrayDeque<E> extends Abstr
658       * @return the number of elements in this deque
659       */
660      public int size() {
661 <        return size;
661 >        return sub(tail, head, elements.length);
662      }
663  
664      /**
# Line 662 | Line 667 | public class ArrayDeque<E> extends Abstr
667       * @return {@code true} if this deque contains no elements
668       */
669      public boolean isEmpty() {
670 <        return size == 0;
670 >        return head == tail;
671      }
672  
673      /**
# Line 686 | Line 691 | public class ArrayDeque<E> extends Abstr
691          int cursor;
692  
693          /** Number of elements yet to be returned. */
694 <        int remaining = size;
694 >        int remaining = size();
695  
696          /**
697           * Index of element returned by most recent call to next.
# Line 701 | Line 706 | public class ArrayDeque<E> extends Abstr
706          }
707  
708          public E next() {
709 <            if (remaining == 0)
709 >            if (remaining <= 0)
710                  throw new NoSuchElementException();
711 <            final Object[] elements = ArrayDeque.this.elements;
712 <            E e = checkedElementAt(elements, cursor);
713 <            lastRet = cursor;
709 <            if (++cursor >= elements.length) cursor = 0;
711 >            final Object[] es = elements;
712 >            E e = nonNullElementAt(es, cursor);
713 >            cursor = inc(lastRet = cursor, es.length);
714              remaining--;
715              return e;
716          }
717  
718          void postDelete(boolean leftShifted) {
719              if (leftShifted)
720 <                if (--cursor < 0) cursor = elements.length - 1;
720 >                cursor = dec(cursor, elements.length);
721          }
722  
723          public final void remove() {
# Line 724 | Line 728 | public class ArrayDeque<E> extends Abstr
728          }
729  
730          public void forEachRemaining(Consumer<? super E> action) {
731 <            int k;
732 <            if ((k = remaining) > 0) {
733 <                remaining = 0;
734 <                ArrayDeque.forEachRemaining(action, elements, cursor, k);
735 <                if ((lastRet = cursor + k - 1) >= elements.length)
736 <                    lastRet -= elements.length;
731 >            Objects.requireNonNull(action);
732 >            int r;
733 >            if ((r = remaining) <= 0)
734 >                return;
735 >            remaining = 0;
736 >            final Object[] es = elements;
737 >            if (es[cursor] == null || sub(tail, cursor, es.length) != r)
738 >                throw new ConcurrentModificationException();
739 >            for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
740 >                 ; i = 0, to = end) {
741 >                for (; i < to; i++)
742 >                    action.accept(elementAt(es, i));
743 >                if (to == end) {
744 >                    if (end != tail)
745 >                        throw new ConcurrentModificationException();
746 >                    lastRet = dec(end, es.length);
747 >                    break;
748 >                }
749              }
750          }
751      }
752  
753      private class DescendingIterator extends DeqIterator {
754 <        DescendingIterator() { cursor = tail(); }
754 >        DescendingIterator() { cursor = dec(tail, elements.length); }
755  
756          public final E next() {
757 <            if (remaining == 0)
757 >            if (remaining <= 0)
758                  throw new NoSuchElementException();
759 <            final Object[] elements = ArrayDeque.this.elements;
760 <            E e = checkedElementAt(elements, cursor);
761 <            lastRet = cursor;
746 <            if (--cursor < 0) cursor = elements.length - 1;
759 >            final Object[] es = elements;
760 >            E e = nonNullElementAt(es, cursor);
761 >            cursor = dec(lastRet = cursor, es.length);
762              remaining--;
763              return e;
764          }
765  
766          void postDelete(boolean leftShifted) {
767              if (!leftShifted)
768 <                if (++cursor >= elements.length) cursor = 0;
768 >                cursor = inc(cursor, elements.length);
769          }
770  
771          public final void forEachRemaining(Consumer<? super E> action) {
772 <            int k;
773 <            if ((k = remaining) > 0) {
774 <                remaining = 0;
775 <                forEachRemainingDescending(action, elements, cursor, k);
776 <                if ((lastRet = cursor - (k - 1)) < 0)
777 <                    lastRet += elements.length;
772 >            Objects.requireNonNull(action);
773 >            int r;
774 >            if ((r = remaining) <= 0)
775 >                return;
776 >            remaining = 0;
777 >            final Object[] es = elements;
778 >            if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
779 >                throw new ConcurrentModificationException();
780 >            for (int i = cursor, end = head, to = (i >= end) ? end : 0;
781 >                 ; i = es.length - 1, to = end) {
782 >                // hotspot generates faster code than for: i >= to !
783 >                for (; i > to - 1; i--)
784 >                    action.accept(elementAt(es, i));
785 >                if (to == end) {
786 >                    if (end != head)
787 >                        throw new ConcurrentModificationException();
788 >                    lastRet = end;
789 >                    break;
790 >                }
791              }
792          }
793      }
# Line 778 | Line 806 | public class ArrayDeque<E> extends Abstr
806       * @since 1.8
807       */
808      public Spliterator<E> spliterator() {
809 <        return new ArrayDequeSpliterator();
809 >        return new DeqSpliterator();
810      }
811  
812 <    final class ArrayDequeSpliterator implements Spliterator<E> {
813 <        private int cursor;
814 <        private int remaining; // -1 until late-binding first use
812 >    final class DeqSpliterator implements Spliterator<E> {
813 >        private int fence;      // -1 until first use
814 >        private int cursor;     // current index, modified on traverse/split
815  
816          /** Constructs late-binding spliterator over all elements. */
817 <        ArrayDequeSpliterator() {
818 <            this.remaining = -1;
817 >        DeqSpliterator() {
818 >            this.fence = -1;
819          }
820  
821 <        /** Constructs spliterator over the given slice. */
822 <        ArrayDequeSpliterator(int cursor, int count) {
823 <            this.cursor = cursor;
824 <            this.remaining = count;
821 >        /** Constructs spliterator over the given range. */
822 >        DeqSpliterator(int origin, int fence) {
823 >            this.cursor = origin;
824 >            this.fence = fence;
825          }
826  
827 <        /** Ensures late-binding initialization; then returns remaining. */
828 <        private int remaining() {
829 <            if (remaining < 0) {
827 >        /** Ensures late-binding initialization; then returns fence. */
828 >        private int getFence() { // force initialization
829 >            int t;
830 >            if ((t = fence) < 0) {
831 >                t = fence = tail;
832                  cursor = head;
803                remaining = size;
833              }
834 <            return remaining;
834 >            return t;
835          }
836  
837 <        public ArrayDequeSpliterator trySplit() {
838 <            final int mid;
839 <            if ((mid = remaining() >> 1) > 0) {
840 <                int oldCursor = cursor;
841 <                cursor = add(cursor, mid, elements.length);
842 <                remaining -= mid;
814 <                return new ArrayDequeSpliterator(oldCursor, mid);
815 <            }
816 <            return null;
837 >        public DeqSpliterator trySplit() {
838 >            final Object[] es = elements;
839 >            final int i, n;
840 >            return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
841 >                ? null
842 >                : new DeqSpliterator(i, cursor = add(i, n, es.length));
843          }
844  
845          public void forEachRemaining(Consumer<? super E> action) {
846 <            int k = remaining(); // side effect!
847 <            remaining = 0;
848 <            ArrayDeque.forEachRemaining(action, elements, cursor, k);
846 >            if (action == null)
847 >                throw new NullPointerException();
848 >            final int end = getFence(), cursor = this.cursor;
849 >            final Object[] es = elements;
850 >            if (cursor != end) {
851 >                this.cursor = end;
852 >                // null check at both ends of range is sufficient
853 >                if (es[cursor] == null || es[dec(end, es.length)] == null)
854 >                    throw new ConcurrentModificationException();
855 >                for (int i = cursor, to = (i <= end) ? end : es.length;
856 >                     ; i = 0, to = end) {
857 >                    for (; i < to; i++)
858 >                        action.accept(elementAt(es, i));
859 >                    if (to == end) break;
860 >                }
861 >            }
862          }
863  
864          public boolean tryAdvance(Consumer<? super E> action) {
865              Objects.requireNonNull(action);
866 <            if (remaining() == 0)
866 >            final Object[] es = elements;
867 >            if (fence < 0) { fence = tail; cursor = head; } // late-binding
868 >            final int i;
869 >            if ((i = cursor) == fence)
870                  return false;
871 <            action.accept(checkedElementAt(elements, cursor));
872 <            if (++cursor >= elements.length) cursor = 0;
873 <            remaining--;
871 >            E e = nonNullElementAt(es, i);
872 >            cursor = inc(i, es.length);
873 >            action.accept(e);
874              return true;
875          }
876  
877          public long estimateSize() {
878 <            return remaining();
878 >            return sub(getFence(), cursor, elements.length);
879          }
880  
881          public int characteristics() {
# Line 844 | Line 886 | public class ArrayDeque<E> extends Abstr
886          }
887      }
888  
847    @SuppressWarnings("unchecked")
889      public void forEach(Consumer<? super E> action) {
890          Objects.requireNonNull(action);
891 <        final Object[] elements = this.elements;
892 <        final int capacity = elements.length;
893 <        int from, end, to, todo;
894 <        todo = (end = (from = head) + size)
895 <            - (to = (capacity - end >= 0) ? end : capacity);
896 <        for (;; from = 0, to = todo, todo = 0) {
897 <            for (int i = from; i < to; i++)
898 <                action.accept((E) elements[i]);
858 <            if (todo == 0) break;
859 <        }
860 <        // checkInvariants();
861 <    }
862 <
863 <    /**
864 <     * A variant of forEach that also checks for concurrent
865 <     * modification, for use in iterators.
866 <     */
867 <    static <E> void forEachRemaining(
868 <        Consumer<? super E> action, Object[] elements, int from, int remaining) {
869 <        Objects.requireNonNull(action);
870 <        final int capacity = elements.length;
871 <        int end, to, todo;
872 <        todo = (end = from + remaining)
873 <            - (to = (capacity - end >= 0) ? end : capacity);
874 <        for (;; from = 0, to = todo, todo = 0) {
875 <            for (int i = from; i < to; i++) {
876 <                @SuppressWarnings("unchecked") E e = (E) elements[i];
877 <                if (e == null)
878 <                    throw new ConcurrentModificationException();
879 <                action.accept(e);
880 <            }
881 <            if (todo == 0) break;
882 <        }
883 <    }
884 <
885 <    static <E> void forEachRemainingDescending(
886 <        Consumer<? super E> action, Object[] elements, int from, int remaining) {
887 <        Objects.requireNonNull(action);
888 <        final int capacity = elements.length;
889 <        int end, to, todo;
890 <        todo = (to = ((end = from - remaining) >= -1) ? end : -1) - end;
891 <        for (;; from = capacity - 1, to = capacity - 1 - todo, todo = 0) {
892 <            for (int i = from; i > to; i--) {
893 <                @SuppressWarnings("unchecked") E e = (E) elements[i];
894 <                if (e == null)
895 <                    throw new ConcurrentModificationException();
896 <                action.accept(e);
891 >        final Object[] es = elements;
892 >        for (int i = head, end = tail, to = (i <= end) ? end : es.length;
893 >             ; i = 0, to = end) {
894 >            for (; i < to; i++)
895 >                action.accept(elementAt(es, i));
896 >            if (to == end) {
897 >                if (end != tail) throw new ConcurrentModificationException();
898 >                break;
899              }
898            if (todo == 0) break;
900          }
901 +        // checkInvariants();
902      }
903  
904      /**
# Line 908 | Line 910 | public class ArrayDeque<E> extends Abstr
910       */
911      /* public */ void replaceAll(UnaryOperator<E> operator) {
912          Objects.requireNonNull(operator);
913 <        final Object[] elements = this.elements;
914 <        final int capacity = elements.length;
915 <        int from, end, to, todo;
916 <        todo = (end = (from = head) + size)
917 <            - (to = (capacity - end >= 0) ? end : capacity);
918 <        for (;; from = 0, to = todo, todo = 0) {
919 <            for (int i = from; i < to; i++)
920 <                elements[i] = operator.apply(elementAt(i));
921 <            if (todo == 0) break;
913 >        final Object[] es = elements;
914 >        for (int i = head, end = tail, to = (i <= end) ? end : es.length;
915 >             ; i = 0, to = end) {
916 >            for (; i < to; i++)
917 >                es[i] = operator.apply(elementAt(es, i));
918 >            if (to == end) {
919 >                if (end != tail) throw new ConcurrentModificationException();
920 >                break;
921 >            }
922          }
923          // checkInvariants();
924      }
# Line 948 | Line 950 | public class ArrayDeque<E> extends Abstr
950      /** Implementation of bulk remove methods. */
951      private boolean bulkRemove(Predicate<? super E> filter) {
952          // checkInvariants();
953 <        final Object[] elements = this.elements;
954 <        final int capacity = elements.length;
955 <        int i = head, j = i, remaining = size, deleted = 0;
956 <        try {
957 <            for (; remaining > 0; remaining--) {
958 <                @SuppressWarnings("unchecked") E e = (E) elements[i];
959 <                if (filter.test(e))
960 <                    deleted++;
961 <                else {
962 <                    if (j != i)
963 <                        elements[j] = e;
964 <                    if (++j >= capacity) j = 0;
965 <                }
966 <                if (++i >= capacity) i = 0;
953 >        final Object[] es = elements;
954 >        // Optimize for initial run of survivors
955 >        for (int i = head, end = tail, to = (i <= end) ? end : es.length;
956 >             ; i = 0, to = end) {
957 >            for (; i < to; i++)
958 >                if (filter.test(elementAt(es, i)))
959 >                    return bulkRemoveModified(filter, i);
960 >            if (to == end) {
961 >                if (end != tail) throw new ConcurrentModificationException();
962 >                break;
963 >            }
964 >        }
965 >        return false;
966 >    }
967 >
968 >    // A tiny bit set implementation
969 >
970 >    private static long[] nBits(int n) {
971 >        return new long[((n - 1) >> 6) + 1];
972 >    }
973 >    private static void setBit(long[] bits, int i) {
974 >        bits[i >> 6] |= 1L << i;
975 >    }
976 >    private static boolean isClear(long[] bits, int i) {
977 >        return (bits[i >> 6] & (1L << i)) == 0;
978 >    }
979 >
980 >    /**
981 >     * Helper for bulkRemove, in case of at least one deletion.
982 >     * Tolerate predicates that reentrantly access the collection for
983 >     * read (but writers still get CME), so traverse once to find
984 >     * elements to delete, a second pass to physically expunge.
985 >     *
986 >     * @param beg valid index of first element to be deleted
987 >     */
988 >    private boolean bulkRemoveModified(
989 >        Predicate<? super E> filter, final int beg) {
990 >        final Object[] es = elements;
991 >        final int capacity = es.length;
992 >        final int end = tail;
993 >        final long[] deathRow = nBits(sub(end, beg, capacity));
994 >        deathRow[0] = 1L;   // set bit 0
995 >        for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
996 >             ; i = 0, to = end, k -= capacity) {
997 >            for (; i < to; i++)
998 >                if (filter.test(elementAt(es, i)))
999 >                    setBit(deathRow, i - k);
1000 >            if (to == end) break;
1001 >        }
1002 >        // a two-finger traversal, with hare i reading, tortoise w writing
1003 >        int w = beg;
1004 >        for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
1005 >             ; w = 0) { // w rejoins i on second leg
1006 >            // In this loop, i and w are on the same leg, with i > w
1007 >            for (; i < to; i++)
1008 >                if (isClear(deathRow, i - k))
1009 >                    es[w++] = es[i];
1010 >            if (to == end) break;
1011 >            // In this loop, w is on the first leg, i on the second
1012 >            for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++)
1013 >                if (isClear(deathRow, i - k))
1014 >                    es[w++] = es[i];
1015 >            if (i >= to) {
1016 >                if (w == capacity) w = 0; // "corner" case
1017 >                break;
1018              }
966            return deleted > 0;
967        } catch (Throwable ex) {
968            if (deleted > 0)
969                for (; remaining > 0; remaining--) {
970                    elements[j] = elements[i];
971                    if (++i >= capacity) i = 0;
972                    if (++j >= capacity) j = 0;
973                }
974            throw ex;
975        } finally {
976            size -= deleted;
977            clearSlice(elements, j, deleted);
978            // checkInvariants();
1019          }
1020 +        if (end != tail) throw new ConcurrentModificationException();
1021 +        circularClear(es, tail = w, end);
1022 +        // checkInvariants();
1023 +        return true;
1024      }
1025  
1026      /**
# Line 989 | Line 1033 | public class ArrayDeque<E> extends Abstr
1033       */
1034      public boolean contains(Object o) {
1035          if (o != null) {
1036 <            final Object[] elements = this.elements;
1037 <            final int capacity = elements.length;
1038 <            int from, end, to, todo;
1039 <            todo = (end = (from = head) + size)
1040 <                - (to = (capacity - end >= 0) ? end : capacity);
997 <            for (;; from = 0, to = todo, todo = 0) {
998 <                for (int i = from; i < to; i++)
999 <                    if (o.equals(elements[i]))
1036 >            final Object[] es = elements;
1037 >            for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1038 >                 ; i = 0, to = end) {
1039 >                for (; i < to; i++)
1040 >                    if (o.equals(es[i]))
1041                          return true;
1042 <                if (todo == 0) break;
1042 >                if (to == end) break;
1043              }
1044          }
1045          return false;
# Line 1026 | Line 1067 | public class ArrayDeque<E> extends Abstr
1067       * The deque will be empty after this call returns.
1068       */
1069      public void clear() {
1070 <        clearSlice(elements, head, size);
1071 <        size = head = 0;
1070 >        circularClear(elements, head, tail);
1071 >        head = tail = 0;
1072          // checkInvariants();
1073      }
1074  
1075      /**
1076 <     * Nulls out count elements, starting at array index from.
1076 >     * Nulls out slots starting at array index i, upto index end.
1077       */
1078 <    private static void clearSlice(Object[] elements, int from, int count) {
1079 <        final int capacity = elements.length, end = from + count;
1080 <        final int leg = (capacity - end >= 0) ? end : capacity;
1081 <        Arrays.fill(elements, from, leg, null);
1082 <        if (leg != end)
1083 <            Arrays.fill(elements, 0, end - capacity, null);
1078 >    private static void circularClear(Object[] es, int i, int end) {
1079 >        for (int to = (i <= end) ? end : es.length;
1080 >             ; i = 0, to = end) {
1081 >            Arrays.fill(es, i, to, null);
1082 >            if (to == end) break;
1083 >        }
1084      }
1085  
1086      /**
# Line 1060 | Line 1101 | public class ArrayDeque<E> extends Abstr
1101      }
1102  
1103      private <T> T[] toArray(Class<T[]> klazz) {
1104 <        final Object[] elements = this.elements;
1064 <        final int capacity = elements.length;
1065 <        final int head = this.head, end = head + size;
1104 >        final Object[] es = elements;
1105          final T[] a;
1106 <        if (end >= 0) {
1107 <            a = Arrays.copyOfRange(elements, head, end, klazz);
1106 >        final int head = this.head, tail = this.tail, end;
1107 >        if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
1108 >            // Uses null extension feature of copyOfRange
1109 >            a = Arrays.copyOfRange(es, head, end, klazz);
1110          } else {
1111              // integer overflow!
1112 <            a = Arrays.copyOfRange(elements, 0, size, klazz);
1113 <            System.arraycopy(elements, head, a, 0, capacity - head);
1112 >            a = Arrays.copyOfRange(es, 0, end - head, klazz);
1113 >            System.arraycopy(es, head, a, 0, es.length - head);
1114          }
1115 <        if (end - capacity > 0)
1116 <            System.arraycopy(elements, 0, a, capacity - head, end - capacity);
1115 >        if (end != tail)
1116 >            System.arraycopy(es, 0, a, es.length - head, tail);
1117          return a;
1118      }
1119  
# Line 1114 | Line 1155 | public class ArrayDeque<E> extends Abstr
1155       */
1156      @SuppressWarnings("unchecked")
1157      public <T> T[] toArray(T[] a) {
1158 <        final int size = this.size;
1159 <        if (size > a.length)
1158 >        final int size;
1159 >        if ((size = size()) > a.length)
1160              return toArray((Class<T[]>) a.getClass());
1161 <        final Object[] elements = this.elements;
1162 <        final int capacity = elements.length;
1163 <        final int head = this.head, end = head + size;
1164 <        final int front = (capacity - end >= 0) ? size : capacity - head;
1165 <        System.arraycopy(elements, head, a, 0, front);
1166 <        if (front != size)
1126 <            System.arraycopy(elements, 0, a, capacity - head, end - capacity);
1161 >        final Object[] es = elements;
1162 >        for (int i = head, j = 0, len = Math.min(size, es.length - i);
1163 >             ; i = 0, len = tail) {
1164 >            System.arraycopy(es, i, a, j, len);
1165 >            if ((j += len) == size) break;
1166 >        }
1167          if (size < a.length)
1168              a[size] = null;
1169          return a;
# Line 1163 | Line 1203 | public class ArrayDeque<E> extends Abstr
1203          s.defaultWriteObject();
1204  
1205          // Write out size
1206 <        s.writeInt(size);
1206 >        s.writeInt(size());
1207  
1208          // Write out elements in order.
1209 <        final Object[] elements = this.elements;
1210 <        final int capacity = elements.length;
1211 <        int from, end, to, todo;
1212 <        todo = (end = (from = head) + size)
1213 <            - (to = (capacity - end >= 0) ? end : capacity);
1214 <        for (;; from = 0, to = todo, todo = 0) {
1175 <            for (int i = from; i < to; i++)
1176 <                s.writeObject(elements[i]);
1177 <            if (todo == 0) break;
1209 >        final Object[] es = elements;
1210 >        for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1211 >             ; i = 0, to = end) {
1212 >            for (; i < to; i++)
1213 >                s.writeObject(es[i]);
1214 >            if (to == end) break;
1215          }
1216      }
1217  
# Line 1190 | Line 1227 | public class ArrayDeque<E> extends Abstr
1227          s.defaultReadObject();
1228  
1229          // Read in size and allocate array
1230 <        elements = new Object[size = s.readInt()];
1230 >        int size = s.readInt();
1231 >        elements = new Object[size + 1];
1232 >        this.tail = size;
1233  
1234          // Read in all elements in the proper order.
1235          for (int i = 0; i < size; i++)
# Line 1199 | Line 1238 | public class ArrayDeque<E> extends Abstr
1238  
1239      /** debugging */
1240      void checkInvariants() {
1241 +        // Use head and tail fields with empty slot at tail strategy.
1242 +        // head == tail disambiguates to "empty".
1243          try {
1244              int capacity = elements.length;
1245 <            // assert size >= 0 && size <= capacity;
1246 <            // assert head >= 0;
1247 <            // assert capacity == 0 || head < capacity;
1248 <            // assert size == 0 || elements[head] != null;
1249 <            // assert size == 0 || elements[tail()] != null;
1250 <            // assert size == capacity || elements[dec(head, capacity)] == null;
1251 <            // assert size == capacity || elements[inc(tail(), capacity)] == null;
1245 >            // assert head >= 0 && head < capacity;
1246 >            // assert tail >= 0 && tail < capacity;
1247 >            // assert capacity > 0;
1248 >            // assert size() < capacity;
1249 >            // assert head == tail || elements[head] != null;
1250 >            // assert elements[tail] == null;
1251 >            // assert head == tail || elements[dec(tail, capacity)] != null;
1252          } catch (Throwable t) {
1253 <            System.err.printf("head=%d size=%d capacity=%d%n",
1254 <                              head, size, elements.length);
1253 >            System.err.printf("head=%d tail=%d capacity=%d%n",
1254 >                              head, tail, elements.length);
1255              System.err.printf("elements=%s%n",
1256                                Arrays.toString(elements));
1257              throw t;

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