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root/jsr166/jsr166/src/main/java/util/ArrayDeque.java

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.109 by jsr166, Sat Nov 5 16:21:06 2016 UTC vs.
Revision 1.123 by jsr166, Sat Nov 26 14:16:18 2016 UTC

#	Line 68 | Line 68 | public class ArrayDeque<E> extends Abstr
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.
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
#	Line 88 | Line 90 | public class ArrayDeque<E> extends Abstr
90
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)).
93	>	* of the deque (via addLast(E), add(E), or push(E));
94	>	* elements[tail] is always null.
95		*/
96		transient int tail;
97
#	Line 187 | 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[Math.max(1, numElements + 1)];
193	>	elements =
194	>	new Object[(numElements < 1) ? 1 :
195	>	(numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
196	>	numElements + 1];
197		}
198
199		/**
#	Line 201 | 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	<	elements = new Object[c.size() + 1];
210	>	this(c.size());
211		addAll(c);
212		}
213
#	Line 224 | 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		* Subtracts j from i, mod modulus.
244	<	* Index i must be logically ahead of j.
245	<	* Returns the "circular distance" from j to i.
246	<	* Precondition and postcondition: 0 <= i < modulus, 0 <= j < 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		static final int sub(int i, int j, int modulus) {
250		if ((i -= j) < 0) i += modulus;
#	Line 314 | 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;
326	<	if ((needed = s + c.size() - elements.length + 1) > 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;
331		}
#	Line 469 | Line 477 | public class ArrayDeque<E> extends Abstr
477		final Object[] es = elements;
478		for (int i = tail, end = head, to = (i >= end) ? end : 0;
479		; i = es.length, to = end) {
480	<	while (--i >= to)
480	>	for (i--; i > to - 1; i--)
481		if (o.equals(es[i])) {
482		delete(i);
483		return true;
#	Line 608 | Line 616 | public class ArrayDeque<E> extends Abstr
616		// checkInvariants();
617		final Object[] es = elements;
618		final int capacity = es.length;
619	<	final int h = head;
619	>	final int h, t;
620		// number of elements before to-be-deleted elt
621	<	final int front = sub(i, h, capacity);
622	<	final int back = size() - front - 1; // number of elements after
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) {
#	Line 627 | Line 636 | public class ArrayDeque<E> extends Abstr
636		return false;
637		} else {
638		// move back elements backwards
639	<	tail = dec(tail, capacity);
639	>	tail = dec(t, capacity);
640		if (i <= tail) {
641		System.arraycopy(es, i + 1, es, i, back);
642		} else { // Wrap around
643	<	int firstLeg = capacity - (i + 1);
635	<	System.arraycopy(es, i + 1, es, i, firstLeg);
643	>	System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
644		es[capacity - 1] = es[0];
645	<	System.arraycopy(es, 1, es, 0, back - firstLeg - 1);
645	>	System.arraycopy(es, 1, es, 0, t - 1);
646		}
647		es[tail] = null;
648		// checkInvariants();
#	Line 702 | Line 710 | public class ArrayDeque<E> extends Abstr
710		throw new NoSuchElementException();
711		final Object[] es = elements;
712		E e = nonNullElementAt(es, cursor);
713	<	lastRet = cursor;
706	<	cursor = inc(cursor, es.length);
713	>	cursor = inc(lastRet = cursor, es.length);
714		remaining--;
715		return e;
716		}
#	Line 751 | Line 758 | public class ArrayDeque<E> extends Abstr
758		throw new NoSuchElementException();
759		final Object[] es = elements;
760		E e = nonNullElementAt(es, cursor);
761	<	lastRet = cursor;
755	<	cursor = dec(cursor, es.length);
761	>	cursor = dec(lastRet = cursor, es.length);
762		remaining--;
763		return e;
764		}
#	Line 773 | Line 779 | public class ArrayDeque<E> extends Abstr
779		throw new ConcurrentModificationException();
780		for (int i = cursor, end = head, to = (i >= end) ? end : 0;
781		; i = es.length - 1, to = end) {
782	<	for (; i >= to; i--)
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 = head;
788	>	lastRet = end;
789		break;
790		}
791		}
#	Line 855 | Line 862 | public class ArrayDeque<E> extends Abstr
862		}
863
864		public boolean tryAdvance(Consumer<? super E> action) {
865	<	if (action == null)
866	<	throw new NullPointerException();
867	<	int t, i;
868	<	if ((t = fence) < 0) t = getFence();
869	<	if (t == (i = cursor))
865	>	Objects.requireNonNull(action);
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	<	final Object[] es;
865	<	action.accept(nonNullElementAt(es = elements, i));
871	>	E e = nonNullElementAt(es, i);
872		cursor = inc(i, es.length);
873	+	action.accept(e);
874		return true;
875		}
876
#	Line 949 | Line 956 | public class ArrayDeque<E> extends Abstr
956		; i = 0, to = end) {
957		for (; i < to; i++)
958		if (filter.test(elementAt(es, i)))
959	<	return bulkRemoveModified(filter, i, to);
959	>	return bulkRemoveModified(filter, i);
960		if (to == end) {
961		if (end != tail) throw new ConcurrentModificationException();
962		break;
#	Line 958 | Line 965 | public class ArrayDeque<E> extends Abstr
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	<	* @param i valid index of first element to be deleted
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, int i, int to) {
989	>	Predicate<? super E> filter, final int beg) {
990		final Object[] es = elements;
991		final int capacity = es.length;
969	–	// a two-finger algorithm, with hare i reading, tortoise j writing
970	–	int j = i++;
992		final int end = tail;
993	<	try {
994	<	for (;; j = 0) {    // j rejoins i on second leg
995	<	E e;
996	<	// In this loop, i and j are on the same leg, with i > j
997	<	for (; i < to; i++)
998	<	if (!filter.test(e = elementAt(es, i)))
999	<	es[j++] = e;
1000	<	if (to == end) break;
1001	<	// In this loop, j is on the first leg, i on the second
1002	<	for (i = 0, to = end; i < to && j < capacity; i++)
1003	<	if (!filter.test(e = elementAt(es, i)))
1004	<	es[j++] = e;
1005	<	if (i >= to) {
1006	<	if (j == capacity) j = 0; // "corner" case
1007	<	break;
1008	<	}
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		}
989	–	return true;
990	–	} catch (Throwable ex) {
991	–	// copy remaining elements
992	–	for (; i != end; i = inc(i, capacity), j = inc(j, capacity))
993	–	es[j] = es[i];
994	–	throw ex;
995	–	} finally {
996	–	if (end != tail) throw new ConcurrentModificationException();
997	–	circularClear(es, tail = j, end);
998	–	// checkInvariants();
1019		}
1020	+	if (end != tail) throw new ConcurrentModificationException();
1021	+	circularClear(es, tail = w, end);
1022	+	// checkInvariants();
1023	+	return true;
1024		}
1025
1026		/**
#	Line 1079 | Line 1103 | public class ArrayDeque<E> extends Abstr
1103		private <T> T[] toArray(Class<T[]> klazz) {
1104		final Object[] es = elements;
1105		final T[] a;
1106	<	final int size = size(), head = this.head, end;
1107	<	final int len = Math.min(size, es.length - head);
1108	<	if ((end = head + size) >= 0) {
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(es, 0, size, klazz);
1113	<	System.arraycopy(es, head, a, 0, len);
1112	>	a = Arrays.copyOfRange(es, 0, end - head, klazz);
1113	>	System.arraycopy(es, head, a, 0, es.length - head);
1114		}
1115	<	if (tail < head)
1116	<	System.arraycopy(es, 0, a, len, tail);
1115	>	if (end != tail)
1116	>	System.arraycopy(es, 0, a, es.length - head, tail);
1117		return a;
1118		}
1119
#	Line 1214 | 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 head >= 0 && head < capacity;

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