| 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; |
| 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; |
