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 |
|
|
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 |
|
|
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 |
|
/** |
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 |
|
|
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; |
325 |
|
final int s = size(), needed; |
326 |
|
if ((needed = s + c.size() - elements.length + 1) > 0) |
327 |
|
grow(needed); |
328 |
< |
c.forEach((e) -> addLast(e)); |
328 |
> |
c.forEach(e -> addLast(e)); |
329 |
|
// checkInvariants(); |
330 |
|
return size() > s; |
331 |
|
} |
787 |
|
if (to == end) { |
788 |
|
if (end != head) |
789 |
|
throw new ConcurrentModificationException(); |
790 |
< |
lastRet = head; |
790 |
> |
lastRet = end; |
791 |
|
break; |
792 |
|
} |
793 |
|
} |
870 |
|
if ((t = fence) < 0) t = getFence(); |
871 |
|
if (t == (i = cursor)) |
872 |
|
return false; |
873 |
< |
final Object[] es; |
866 |
< |
action.accept(nonNullElementAt(es = elements, i)); |
873 |
> |
final Object[] es = elements; |
874 |
|
cursor = inc(i, es.length); |
875 |
+ |
action.accept(nonNullElementAt(es, i)); |
876 |
|
return true; |
877 |
|
} |
878 |
|
|
958 |
|
; i = 0, to = end) { |
959 |
|
for (; i < to; i++) |
960 |
|
if (filter.test(elementAt(es, i))) |
961 |
< |
return bulkRemoveModified(filter, i, to); |
961 |
> |
return bulkRemoveModified(filter, i); |
962 |
|
if (to == end) { |
963 |
|
if (end != tail) throw new ConcurrentModificationException(); |
964 |
|
break; |
967 |
|
return false; |
968 |
|
} |
969 |
|
|
970 |
+ |
// A tiny bit set implementation |
971 |
+ |
|
972 |
+ |
private static long[] nBits(int n) { |
973 |
+ |
return new long[((n - 1) >> 6) + 1]; |
974 |
+ |
} |
975 |
+ |
private static void setBit(long[] bits, int i) { |
976 |
+ |
bits[i >> 6] |= 1L << i; |
977 |
+ |
} |
978 |
+ |
private static boolean isClear(long[] bits, int i) { |
979 |
+ |
return (bits[i >> 6] & (1L << i)) == 0; |
980 |
+ |
} |
981 |
+ |
|
982 |
|
/** |
983 |
|
* Helper for bulkRemove, in case of at least one deletion. |
984 |
< |
* @param i valid index of first element to be deleted |
984 |
> |
* Tolerate predicates that reentrantly access the collection for |
985 |
> |
* read (but writers still get CME), so traverse once to find |
986 |
> |
* elements to delete, a second pass to physically expunge. |
987 |
> |
* |
988 |
> |
* @param beg valid index of first element to be deleted |
989 |
|
*/ |
990 |
|
private boolean bulkRemoveModified( |
991 |
< |
Predicate<? super E> filter, int i, int to) { |
991 |
> |
Predicate<? super E> filter, final int beg) { |
992 |
|
final Object[] es = elements; |
993 |
|
final int capacity = es.length; |
970 |
– |
// a two-finger algorithm, with hare i reading, tortoise j writing |
971 |
– |
int j = i++; |
994 |
|
final int end = tail; |
995 |
< |
try { |
996 |
< |
for (;; j = 0) { // j rejoins i on second leg |
997 |
< |
E e; |
998 |
< |
// In this loop, i and j are on the same leg, with i > j |
999 |
< |
for (; i < to; i++) |
1000 |
< |
if (!filter.test(e = elementAt(es, i))) |
1001 |
< |
es[j++] = e; |
1002 |
< |
if (to == end) break; |
1003 |
< |
// In this loop, j is on the first leg, i on the second |
1004 |
< |
for (i = 0, to = end; i < to && j < capacity; i++) |
1005 |
< |
if (!filter.test(e = elementAt(es, i))) |
1006 |
< |
es[j++] = e; |
1007 |
< |
if (i >= to) { |
1008 |
< |
if (j == capacity) j = 0; // "corner" case |
1009 |
< |
break; |
1010 |
< |
} |
995 |
> |
final long[] deathRow = nBits(sub(end, beg, capacity)); |
996 |
> |
deathRow[0] = 1L; // set bit 0 |
997 |
> |
for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg; |
998 |
> |
; i = 0, to = end, k -= capacity) { |
999 |
> |
for (; i < to; i++) |
1000 |
> |
if (filter.test(elementAt(es, i))) |
1001 |
> |
setBit(deathRow, i - k); |
1002 |
> |
if (to == end) break; |
1003 |
> |
} |
1004 |
> |
// a two-finger traversal, with hare i reading, tortoise w writing |
1005 |
> |
int w = beg; |
1006 |
> |
for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg; |
1007 |
> |
; w = 0) { // w rejoins i on second leg |
1008 |
> |
// In this loop, i and w are on the same leg, with i > w |
1009 |
> |
for (; i < to; i++) |
1010 |
> |
if (isClear(deathRow, i - k)) |
1011 |
> |
es[w++] = es[i]; |
1012 |
> |
if (to == end) break; |
1013 |
> |
// In this loop, w is on the first leg, i on the second |
1014 |
> |
for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++) |
1015 |
> |
if (isClear(deathRow, i - k)) |
1016 |
> |
es[w++] = es[i]; |
1017 |
> |
if (i >= to) { |
1018 |
> |
if (w == capacity) w = 0; // "corner" case |
1019 |
> |
break; |
1020 |
|
} |
990 |
– |
return true; |
991 |
– |
} catch (Throwable ex) { |
992 |
– |
// copy remaining elements |
993 |
– |
for (; i != end; i = inc(i, capacity), j = inc(j, capacity)) |
994 |
– |
es[j] = es[i]; |
995 |
– |
throw ex; |
996 |
– |
} finally { |
997 |
– |
if (end != tail) throw new ConcurrentModificationException(); |
998 |
– |
circularClear(es, tail = j, end); |
999 |
– |
// checkInvariants(); |
1021 |
|
} |
1022 |
+ |
if (end != tail) throw new ConcurrentModificationException(); |
1023 |
+ |
circularClear(es, tail = w, end); |
1024 |
+ |
// checkInvariants(); |
1025 |
+ |
return true; |
1026 |
|
} |
1027 |
|
|
1028 |
|
/** |
1240 |
|
|
1241 |
|
/** debugging */ |
1242 |
|
void checkInvariants() { |
1243 |
+ |
// Use head and tail fields with empty slot at tail strategy. |
1244 |
+ |
// head == tail disambiguates to "empty". |
1245 |
|
try { |
1246 |
|
int capacity = elements.length; |
1247 |
|
// assert head >= 0 && head < capacity; |