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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.lang.invoke.MethodHandles; |
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import java.lang.invoke.VarHandle; |
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import java.util.AbstractQueue; |
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import java.util.Arrays; |
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import java.util.Collection; |
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import java.util.Comparator; |
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import java.util.Iterator; |
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import java.util.NoSuchElementException; |
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import java.util.Objects; |
18 |
import java.util.PriorityQueue; |
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import java.util.Queue; |
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import java.util.SortedSet; |
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import java.util.Spliterator; |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.function.Consumer; |
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import jdk.internal.misc.SharedSecrets; |
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|
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/** |
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* An unbounded {@linkplain BlockingQueue blocking queue} that uses |
29 |
* the same ordering rules as class {@link PriorityQueue} and supplies |
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* blocking retrieval operations. While this queue is logically |
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* unbounded, attempted additions may fail due to resource exhaustion |
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* (causing {@code OutOfMemoryError}). This class does not permit |
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* {@code null} elements. A priority queue relying on {@linkplain |
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* Comparable natural ordering} also does not permit insertion of |
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* non-comparable objects (doing so results in |
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* {@code ClassCastException}). |
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* |
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* <p>This class and its iterator implement all of the <em>optional</em> |
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* methods of the {@link Collection} and {@link Iterator} interfaces. |
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* The Iterator provided in method {@link #iterator()} and the |
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* Spliterator provided in method {@link #spliterator()} are <em>not</em> |
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* guaranteed to traverse the elements of the PriorityBlockingQueue in |
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* any particular order. If you need ordered traversal, consider using |
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* {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo} can |
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* be used to <em>remove</em> some or all elements in priority order and |
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* place them in another collection. |
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* |
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* <p>Operations on this class make no guarantees about the ordering |
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* of elements with equal priority. If you need to enforce an |
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* ordering, you can define custom classes or comparators that use a |
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* secondary key to break ties in primary priority values. For |
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* example, here is a class that applies first-in-first-out |
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* tie-breaking to comparable elements. To use it, you would insert a |
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* {@code new FIFOEntry(anEntry)} instead of a plain entry object. |
55 |
* |
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* <pre> {@code |
57 |
* class FIFOEntry<E extends Comparable<? super E>> |
58 |
* implements Comparable<FIFOEntry<E>> { |
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* static final AtomicLong seq = new AtomicLong(0); |
60 |
* final long seqNum; |
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* final E entry; |
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* public FIFOEntry(E entry) { |
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* seqNum = seq.getAndIncrement(); |
64 |
* this.entry = entry; |
65 |
* } |
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* public E getEntry() { return entry; } |
67 |
* public int compareTo(FIFOEntry<E> other) { |
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* int res = entry.compareTo(other.entry); |
69 |
* if (res == 0 && other.entry != this.entry) |
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* res = (seqNum < other.seqNum ? -1 : 1); |
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* return res; |
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* } |
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* }}</pre> |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <E> the type of elements held in this queue |
82 |
*/ |
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@SuppressWarnings("unchecked") |
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public class PriorityBlockingQueue<E> extends AbstractQueue<E> |
85 |
implements BlockingQueue<E>, java.io.Serializable { |
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private static final long serialVersionUID = 5595510919245408276L; |
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|
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/* |
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* The implementation uses an array-based binary heap, with public |
90 |
* operations protected with a single lock. However, allocation |
91 |
* during resizing uses a simple spinlock (used only while not |
92 |
* holding main lock) in order to allow takes to operate |
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* concurrently with allocation. This avoids repeated |
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* postponement of waiting consumers and consequent element |
95 |
* build-up. The need to back away from lock during allocation |
96 |
* makes it impossible to simply wrap delegated |
97 |
* java.util.PriorityQueue operations within a lock, as was done |
98 |
* in a previous version of this class. To maintain |
99 |
* interoperability, a plain PriorityQueue is still used during |
100 |
* serialization, which maintains compatibility at the expense of |
101 |
* transiently doubling overhead. |
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*/ |
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|
104 |
/** |
105 |
* Default array capacity. |
106 |
*/ |
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private static final int DEFAULT_INITIAL_CAPACITY = 11; |
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|
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/** |
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* The maximum size of array to allocate. |
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* Some VMs reserve some header words in an array. |
112 |
* Attempts to allocate larger arrays may result in |
113 |
* OutOfMemoryError: Requested array size exceeds VM limit |
114 |
*/ |
115 |
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; |
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|
117 |
/** |
118 |
* Priority queue represented as a balanced binary heap: the two |
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* children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The |
120 |
* priority queue is ordered by comparator, or by the elements' |
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* natural ordering, if comparator is null: For each node n in the |
122 |
* heap and each descendant d of n, n <= d. The element with the |
123 |
* lowest value is in queue[0], assuming the queue is nonempty. |
124 |
*/ |
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private transient Object[] queue; |
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|
127 |
/** |
128 |
* The number of elements in the priority queue. |
129 |
*/ |
130 |
private transient int size; |
131 |
|
132 |
/** |
133 |
* The comparator, or null if priority queue uses elements' |
134 |
* natural ordering. |
135 |
*/ |
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private transient Comparator<? super E> comparator; |
137 |
|
138 |
/** |
139 |
* Lock used for all public operations. |
140 |
*/ |
141 |
private final ReentrantLock lock = new ReentrantLock(); |
142 |
|
143 |
/** |
144 |
* Condition for blocking when empty. |
145 |
*/ |
146 |
private final Condition notEmpty = lock.newCondition(); |
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|
148 |
/** |
149 |
* Spinlock for allocation, acquired via CAS. |
150 |
*/ |
151 |
private transient volatile int allocationSpinLock; |
152 |
|
153 |
/** |
154 |
* A plain PriorityQueue used only for serialization, |
155 |
* to maintain compatibility with previous versions |
156 |
* of this class. Non-null only during serialization/deserialization. |
157 |
*/ |
158 |
private PriorityQueue<E> q; |
159 |
|
160 |
/** |
161 |
* Creates a {@code PriorityBlockingQueue} with the default |
162 |
* initial capacity (11) that orders its elements according to |
163 |
* their {@linkplain Comparable natural ordering}. |
164 |
*/ |
165 |
public PriorityBlockingQueue() { |
166 |
this(DEFAULT_INITIAL_CAPACITY, null); |
167 |
} |
168 |
|
169 |
/** |
170 |
* Creates a {@code PriorityBlockingQueue} with the specified |
171 |
* initial capacity that orders its elements according to their |
172 |
* {@linkplain Comparable natural ordering}. |
173 |
* |
174 |
* @param initialCapacity the initial capacity for this priority queue |
175 |
* @throws IllegalArgumentException if {@code initialCapacity} is less |
176 |
* than 1 |
177 |
*/ |
178 |
public PriorityBlockingQueue(int initialCapacity) { |
179 |
this(initialCapacity, null); |
180 |
} |
181 |
|
182 |
/** |
183 |
* Creates a {@code PriorityBlockingQueue} with the specified initial |
184 |
* capacity that orders its elements according to the specified |
185 |
* comparator. |
186 |
* |
187 |
* @param initialCapacity the initial capacity for this priority queue |
188 |
* @param comparator the comparator that will be used to order this |
189 |
* priority queue. If {@code null}, the {@linkplain Comparable |
190 |
* natural ordering} of the elements will be used. |
191 |
* @throws IllegalArgumentException if {@code initialCapacity} is less |
192 |
* than 1 |
193 |
*/ |
194 |
public PriorityBlockingQueue(int initialCapacity, |
195 |
Comparator<? super E> comparator) { |
196 |
if (initialCapacity < 1) |
197 |
throw new IllegalArgumentException(); |
198 |
this.comparator = comparator; |
199 |
this.queue = new Object[Math.max(1, initialCapacity)]; |
200 |
} |
201 |
|
202 |
/** |
203 |
* Creates a {@code PriorityBlockingQueue} containing the elements |
204 |
* in the specified collection. If the specified collection is a |
205 |
* {@link SortedSet} or a {@link PriorityQueue}, this |
206 |
* priority queue will be ordered according to the same ordering. |
207 |
* Otherwise, this priority queue will be ordered according to the |
208 |
* {@linkplain Comparable natural ordering} of its elements. |
209 |
* |
210 |
* @param c the collection whose elements are to be placed |
211 |
* into this priority queue |
212 |
* @throws ClassCastException if elements of the specified collection |
213 |
* cannot be compared to one another according to the priority |
214 |
* queue's ordering |
215 |
* @throws NullPointerException if the specified collection or any |
216 |
* of its elements are null |
217 |
*/ |
218 |
public PriorityBlockingQueue(Collection<? extends E> c) { |
219 |
boolean heapify = true; // true if not known to be in heap order |
220 |
boolean screen = true; // true if must screen for nulls |
221 |
if (c instanceof SortedSet<?>) { |
222 |
SortedSet<? extends E> ss = (SortedSet<? extends E>) c; |
223 |
this.comparator = (Comparator<? super E>) ss.comparator(); |
224 |
heapify = false; |
225 |
} |
226 |
else if (c instanceof PriorityBlockingQueue<?>) { |
227 |
PriorityBlockingQueue<? extends E> pq = |
228 |
(PriorityBlockingQueue<? extends E>) c; |
229 |
this.comparator = (Comparator<? super E>) pq.comparator(); |
230 |
screen = false; |
231 |
if (pq.getClass() == PriorityBlockingQueue.class) // exact match |
232 |
heapify = false; |
233 |
} |
234 |
Object[] es = c.toArray(); |
235 |
int n = es.length; |
236 |
// If c.toArray incorrectly doesn't return Object[], copy it. |
237 |
if (es.getClass() != Object[].class) |
238 |
es = Arrays.copyOf(es, n, Object[].class); |
239 |
if (screen && (n == 1 || this.comparator != null)) { |
240 |
for (Object e : es) |
241 |
if (e == null) |
242 |
throw new NullPointerException(); |
243 |
} |
244 |
this.queue = ensureNonEmpty(es); |
245 |
this.size = n; |
246 |
if (heapify) |
247 |
heapify(); |
248 |
} |
249 |
|
250 |
/** Ensures that queue[0] exists, helping peek() and poll(). */ |
251 |
private static Object[] ensureNonEmpty(Object[] es) { |
252 |
return (es.length > 0) ? es : new Object[1]; |
253 |
} |
254 |
|
255 |
/** |
256 |
* Tries to grow array to accommodate at least one more element |
257 |
* (but normally expand by about 50%), giving up (allowing retry) |
258 |
* on contention (which we expect to be rare). Call only while |
259 |
* holding lock. |
260 |
* |
261 |
* @param array the heap array |
262 |
* @param oldCap the length of the array |
263 |
*/ |
264 |
private void tryGrow(Object[] array, int oldCap) { |
265 |
lock.unlock(); // must release and then re-acquire main lock |
266 |
Object[] newArray = null; |
267 |
if (allocationSpinLock == 0 && |
268 |
ALLOCATIONSPINLOCK.compareAndSet(this, 0, 1)) { |
269 |
try { |
270 |
int newCap = oldCap + ((oldCap < 64) ? |
271 |
(oldCap + 2) : // grow faster if small |
272 |
(oldCap >> 1)); |
273 |
if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow |
274 |
int minCap = oldCap + 1; |
275 |
if (minCap < 0 || minCap > MAX_ARRAY_SIZE) |
276 |
throw new OutOfMemoryError(); |
277 |
newCap = MAX_ARRAY_SIZE; |
278 |
} |
279 |
if (newCap > oldCap && queue == array) |
280 |
newArray = new Object[newCap]; |
281 |
} finally { |
282 |
allocationSpinLock = 0; |
283 |
} |
284 |
} |
285 |
if (newArray == null) // back off if another thread is allocating |
286 |
Thread.yield(); |
287 |
lock.lock(); |
288 |
if (newArray != null && queue == array) { |
289 |
queue = newArray; |
290 |
System.arraycopy(array, 0, newArray, 0, oldCap); |
291 |
} |
292 |
} |
293 |
|
294 |
/** |
295 |
* Mechanics for poll(). Call only while holding lock. |
296 |
*/ |
297 |
private E dequeue() { |
298 |
// assert lock.isHeldByCurrentThread(); |
299 |
final Object[] es; |
300 |
final E result; |
301 |
|
302 |
if ((result = (E) ((es = queue)[0])) != null) { |
303 |
final int n; |
304 |
final E x = (E) es[(n = --size)]; |
305 |
es[n] = null; |
306 |
if (n > 0) { |
307 |
final Comparator<? super E> cmp; |
308 |
if ((cmp = comparator) == null) |
309 |
siftDownComparable(0, x, es, n); |
310 |
else |
311 |
siftDownUsingComparator(0, x, es, n, cmp); |
312 |
} |
313 |
} |
314 |
return result; |
315 |
} |
316 |
|
317 |
/** |
318 |
* Inserts item x at position k, maintaining heap invariant by |
319 |
* promoting x up the tree until it is greater than or equal to |
320 |
* its parent, or is the root. |
321 |
* |
322 |
* To simplify and speed up coercions and comparisons, the |
323 |
* Comparable and Comparator versions are separated into different |
324 |
* methods that are otherwise identical. (Similarly for siftDown.) |
325 |
* |
326 |
* @param k the position to fill |
327 |
* @param x the item to insert |
328 |
* @param es the heap array |
329 |
*/ |
330 |
private static <T> void siftUpComparable(int k, T x, Object[] es) { |
331 |
Comparable<? super T> key = (Comparable<? super T>) x; |
332 |
while (k > 0) { |
333 |
int parent = (k - 1) >>> 1; |
334 |
Object e = es[parent]; |
335 |
if (key.compareTo((T) e) >= 0) |
336 |
break; |
337 |
es[k] = e; |
338 |
k = parent; |
339 |
} |
340 |
es[k] = key; |
341 |
} |
342 |
|
343 |
private static <T> void siftUpUsingComparator( |
344 |
int k, T x, Object[] es, Comparator<? super T> cmp) { |
345 |
while (k > 0) { |
346 |
int parent = (k - 1) >>> 1; |
347 |
Object e = es[parent]; |
348 |
if (cmp.compare(x, (T) e) >= 0) |
349 |
break; |
350 |
es[k] = e; |
351 |
k = parent; |
352 |
} |
353 |
es[k] = x; |
354 |
} |
355 |
|
356 |
/** |
357 |
* Inserts item x at position k, maintaining heap invariant by |
358 |
* demoting x down the tree repeatedly until it is less than or |
359 |
* equal to its children or is a leaf. |
360 |
* |
361 |
* @param k the position to fill |
362 |
* @param x the item to insert |
363 |
* @param es the heap array |
364 |
* @param n heap size |
365 |
*/ |
366 |
private static <T> void siftDownComparable(int k, T x, Object[] es, int n) { |
367 |
// assert n > 0; |
368 |
Comparable<? super T> key = (Comparable<? super T>)x; |
369 |
int half = n >>> 1; // loop while a non-leaf |
370 |
while (k < half) { |
371 |
int child = (k << 1) + 1; // assume left child is least |
372 |
Object c = es[child]; |
373 |
int right = child + 1; |
374 |
if (right < n && |
375 |
((Comparable<? super T>) c).compareTo((T) es[right]) > 0) |
376 |
c = es[child = right]; |
377 |
if (key.compareTo((T) c) <= 0) |
378 |
break; |
379 |
es[k] = c; |
380 |
k = child; |
381 |
} |
382 |
es[k] = key; |
383 |
} |
384 |
|
385 |
private static <T> void siftDownUsingComparator( |
386 |
int k, T x, Object[] es, int n, Comparator<? super T> cmp) { |
387 |
// assert n > 0; |
388 |
int half = n >>> 1; |
389 |
while (k < half) { |
390 |
int child = (k << 1) + 1; |
391 |
Object c = es[child]; |
392 |
int right = child + 1; |
393 |
if (right < n && cmp.compare((T) c, (T) es[right]) > 0) |
394 |
c = es[child = right]; |
395 |
if (cmp.compare(x, (T) c) <= 0) |
396 |
break; |
397 |
es[k] = c; |
398 |
k = child; |
399 |
} |
400 |
es[k] = x; |
401 |
} |
402 |
|
403 |
/** |
404 |
* Establishes the heap invariant (described above) in the entire tree, |
405 |
* assuming nothing about the order of the elements prior to the call. |
406 |
* This classic algorithm due to Floyd (1964) is known to be O(size). |
407 |
*/ |
408 |
private void heapify() { |
409 |
final Object[] es = queue; |
410 |
int n = size, i = (n >>> 1) - 1; |
411 |
final Comparator<? super E> cmp; |
412 |
if ((cmp = comparator) == null) |
413 |
for (; i >= 0; i--) |
414 |
siftDownComparable(i, (E) es[i], es, n); |
415 |
else |
416 |
for (; i >= 0; i--) |
417 |
siftDownUsingComparator(i, (E) es[i], es, n, cmp); |
418 |
} |
419 |
|
420 |
/** |
421 |
* Inserts the specified element into this priority queue. |
422 |
* |
423 |
* @param e the element to add |
424 |
* @return {@code true} (as specified by {@link Collection#add}) |
425 |
* @throws ClassCastException if the specified element cannot be compared |
426 |
* with elements currently in the priority queue according to the |
427 |
* priority queue's ordering |
428 |
* @throws NullPointerException if the specified element is null |
429 |
*/ |
430 |
public boolean add(E e) { |
431 |
return offer(e); |
432 |
} |
433 |
|
434 |
/** |
435 |
* Inserts the specified element into this priority queue. |
436 |
* As the queue is unbounded, this method will never return {@code false}. |
437 |
* |
438 |
* @param e the element to add |
439 |
* @return {@code true} (as specified by {@link Queue#offer}) |
440 |
* @throws ClassCastException if the specified element cannot be compared |
441 |
* with elements currently in the priority queue according to the |
442 |
* priority queue's ordering |
443 |
* @throws NullPointerException if the specified element is null |
444 |
*/ |
445 |
public boolean offer(E e) { |
446 |
if (e == null) |
447 |
throw new NullPointerException(); |
448 |
final ReentrantLock lock = this.lock; |
449 |
lock.lock(); |
450 |
int n, cap; |
451 |
Object[] es; |
452 |
while ((n = size) >= (cap = (es = queue).length)) |
453 |
tryGrow(es, cap); |
454 |
try { |
455 |
final Comparator<? super E> cmp; |
456 |
if ((cmp = comparator) == null) |
457 |
siftUpComparable(n, e, es); |
458 |
else |
459 |
siftUpUsingComparator(n, e, es, cmp); |
460 |
size = n + 1; |
461 |
notEmpty.signal(); |
462 |
} finally { |
463 |
lock.unlock(); |
464 |
} |
465 |
return true; |
466 |
} |
467 |
|
468 |
/** |
469 |
* Inserts the specified element into this priority queue. |
470 |
* As the queue is unbounded, this method will never block. |
471 |
* |
472 |
* @param e the element to add |
473 |
* @throws ClassCastException if the specified element cannot be compared |
474 |
* with elements currently in the priority queue according to the |
475 |
* priority queue's ordering |
476 |
* @throws NullPointerException if the specified element is null |
477 |
*/ |
478 |
public void put(E e) { |
479 |
offer(e); // never need to block |
480 |
} |
481 |
|
482 |
/** |
483 |
* Inserts the specified element into this priority queue. |
484 |
* As the queue is unbounded, this method will never block or |
485 |
* return {@code false}. |
486 |
* |
487 |
* @param e the element to add |
488 |
* @param timeout This parameter is ignored as the method never blocks |
489 |
* @param unit This parameter is ignored as the method never blocks |
490 |
* @return {@code true} (as specified by |
491 |
* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
492 |
* @throws ClassCastException if the specified element cannot be compared |
493 |
* with elements currently in the priority queue according to the |
494 |
* priority queue's ordering |
495 |
* @throws NullPointerException if the specified element is null |
496 |
*/ |
497 |
public boolean offer(E e, long timeout, TimeUnit unit) { |
498 |
return offer(e); // never need to block |
499 |
} |
500 |
|
501 |
public E poll() { |
502 |
final ReentrantLock lock = this.lock; |
503 |
lock.lock(); |
504 |
try { |
505 |
return dequeue(); |
506 |
} finally { |
507 |
lock.unlock(); |
508 |
} |
509 |
} |
510 |
|
511 |
public E take() throws InterruptedException { |
512 |
final ReentrantLock lock = this.lock; |
513 |
lock.lockInterruptibly(); |
514 |
E result; |
515 |
try { |
516 |
while ( (result = dequeue()) == null) |
517 |
notEmpty.await(); |
518 |
} finally { |
519 |
lock.unlock(); |
520 |
} |
521 |
return result; |
522 |
} |
523 |
|
524 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
525 |
long nanos = unit.toNanos(timeout); |
526 |
final ReentrantLock lock = this.lock; |
527 |
lock.lockInterruptibly(); |
528 |
E result; |
529 |
try { |
530 |
while ( (result = dequeue()) == null && nanos > 0) |
531 |
nanos = notEmpty.awaitNanos(nanos); |
532 |
} finally { |
533 |
lock.unlock(); |
534 |
} |
535 |
return result; |
536 |
} |
537 |
|
538 |
public E peek() { |
539 |
final ReentrantLock lock = this.lock; |
540 |
lock.lock(); |
541 |
try { |
542 |
return (E) queue[0]; |
543 |
} finally { |
544 |
lock.unlock(); |
545 |
} |
546 |
} |
547 |
|
548 |
/** |
549 |
* Returns the comparator used to order the elements in this queue, |
550 |
* or {@code null} if this queue uses the {@linkplain Comparable |
551 |
* natural ordering} of its elements. |
552 |
* |
553 |
* @return the comparator used to order the elements in this queue, |
554 |
* or {@code null} if this queue uses the natural |
555 |
* ordering of its elements |
556 |
*/ |
557 |
public Comparator<? super E> comparator() { |
558 |
return comparator; |
559 |
} |
560 |
|
561 |
public int size() { |
562 |
final ReentrantLock lock = this.lock; |
563 |
lock.lock(); |
564 |
try { |
565 |
return size; |
566 |
} finally { |
567 |
lock.unlock(); |
568 |
} |
569 |
} |
570 |
|
571 |
/** |
572 |
* Always returns {@code Integer.MAX_VALUE} because |
573 |
* a {@code PriorityBlockingQueue} is not capacity constrained. |
574 |
* @return {@code Integer.MAX_VALUE} always |
575 |
*/ |
576 |
public int remainingCapacity() { |
577 |
return Integer.MAX_VALUE; |
578 |
} |
579 |
|
580 |
private int indexOf(Object o) { |
581 |
if (o != null) { |
582 |
final Object[] es = queue; |
583 |
for (int i = 0, n = size; i < n; i++) |
584 |
if (o.equals(es[i])) |
585 |
return i; |
586 |
} |
587 |
return -1; |
588 |
} |
589 |
|
590 |
/** |
591 |
* Removes the ith element from queue. |
592 |
*/ |
593 |
private void removeAt(int i) { |
594 |
final Object[] es = queue; |
595 |
final int n = size - 1; |
596 |
if (n == i) // removed last element |
597 |
es[i] = null; |
598 |
else { |
599 |
E moved = (E) es[n]; |
600 |
es[n] = null; |
601 |
final Comparator<? super E> cmp; |
602 |
if ((cmp = comparator) == null) |
603 |
siftDownComparable(i, moved, es, n); |
604 |
else |
605 |
siftDownUsingComparator(i, moved, es, n, cmp); |
606 |
if (es[i] == moved) { |
607 |
if (cmp == null) |
608 |
siftUpComparable(i, moved, es); |
609 |
else |
610 |
siftUpUsingComparator(i, moved, es, cmp); |
611 |
} |
612 |
} |
613 |
size = n; |
614 |
} |
615 |
|
616 |
/** |
617 |
* Removes a single instance of the specified element from this queue, |
618 |
* if it is present. More formally, removes an element {@code e} such |
619 |
* that {@code o.equals(e)}, if this queue contains one or more such |
620 |
* elements. Returns {@code true} if and only if this queue contained |
621 |
* the specified element (or equivalently, if this queue changed as a |
622 |
* result of the call). |
623 |
* |
624 |
* @param o element to be removed from this queue, if present |
625 |
* @return {@code true} if this queue changed as a result of the call |
626 |
*/ |
627 |
public boolean remove(Object o) { |
628 |
final ReentrantLock lock = this.lock; |
629 |
lock.lock(); |
630 |
try { |
631 |
int i = indexOf(o); |
632 |
if (i == -1) |
633 |
return false; |
634 |
removeAt(i); |
635 |
return true; |
636 |
} finally { |
637 |
lock.unlock(); |
638 |
} |
639 |
} |
640 |
|
641 |
/** |
642 |
* Identity-based version for use in Itr.remove. |
643 |
* |
644 |
* @param o element to be removed from this queue, if present |
645 |
*/ |
646 |
void removeEq(Object o) { |
647 |
final ReentrantLock lock = this.lock; |
648 |
lock.lock(); |
649 |
try { |
650 |
final Object[] es = queue; |
651 |
for (int i = 0, n = size; i < n; i++) { |
652 |
if (o == es[i]) { |
653 |
removeAt(i); |
654 |
break; |
655 |
} |
656 |
} |
657 |
} finally { |
658 |
lock.unlock(); |
659 |
} |
660 |
} |
661 |
|
662 |
/** |
663 |
* Returns {@code true} if this queue contains the specified element. |
664 |
* More formally, returns {@code true} if and only if this queue contains |
665 |
* at least one element {@code e} such that {@code o.equals(e)}. |
666 |
* |
667 |
* @param o object to be checked for containment in this queue |
668 |
* @return {@code true} if this queue contains the specified element |
669 |
*/ |
670 |
public boolean contains(Object o) { |
671 |
final ReentrantLock lock = this.lock; |
672 |
lock.lock(); |
673 |
try { |
674 |
return indexOf(o) != -1; |
675 |
} finally { |
676 |
lock.unlock(); |
677 |
} |
678 |
} |
679 |
|
680 |
public String toString() { |
681 |
return Helpers.collectionToString(this); |
682 |
} |
683 |
|
684 |
/** |
685 |
* @throws UnsupportedOperationException {@inheritDoc} |
686 |
* @throws ClassCastException {@inheritDoc} |
687 |
* @throws NullPointerException {@inheritDoc} |
688 |
* @throws IllegalArgumentException {@inheritDoc} |
689 |
*/ |
690 |
public int drainTo(Collection<? super E> c) { |
691 |
return drainTo(c, Integer.MAX_VALUE); |
692 |
} |
693 |
|
694 |
/** |
695 |
* @throws UnsupportedOperationException {@inheritDoc} |
696 |
* @throws ClassCastException {@inheritDoc} |
697 |
* @throws NullPointerException {@inheritDoc} |
698 |
* @throws IllegalArgumentException {@inheritDoc} |
699 |
*/ |
700 |
public int drainTo(Collection<? super E> c, int maxElements) { |
701 |
Objects.requireNonNull(c); |
702 |
if (c == this) |
703 |
throw new IllegalArgumentException(); |
704 |
if (maxElements <= 0) |
705 |
return 0; |
706 |
final ReentrantLock lock = this.lock; |
707 |
lock.lock(); |
708 |
try { |
709 |
int n = Math.min(size, maxElements); |
710 |
for (int i = 0; i < n; i++) { |
711 |
c.add((E) queue[0]); // In this order, in case add() throws. |
712 |
dequeue(); |
713 |
} |
714 |
return n; |
715 |
} finally { |
716 |
lock.unlock(); |
717 |
} |
718 |
} |
719 |
|
720 |
/** |
721 |
* Atomically removes all of the elements from this queue. |
722 |
* The queue will be empty after this call returns. |
723 |
*/ |
724 |
public void clear() { |
725 |
final ReentrantLock lock = this.lock; |
726 |
lock.lock(); |
727 |
try { |
728 |
final Object[] es = queue; |
729 |
for (int i = 0, n = size; i < n; i++) |
730 |
es[i] = null; |
731 |
size = 0; |
732 |
} finally { |
733 |
lock.unlock(); |
734 |
} |
735 |
} |
736 |
|
737 |
/** |
738 |
* Returns an array containing all of the elements in this queue. |
739 |
* The returned array elements are in no particular order. |
740 |
* |
741 |
* <p>The returned array will be "safe" in that no references to it are |
742 |
* maintained by this queue. (In other words, this method must allocate |
743 |
* a new array). The caller is thus free to modify the returned array. |
744 |
* |
745 |
* <p>This method acts as bridge between array-based and collection-based |
746 |
* APIs. |
747 |
* |
748 |
* @return an array containing all of the elements in this queue |
749 |
*/ |
750 |
public Object[] toArray() { |
751 |
final ReentrantLock lock = this.lock; |
752 |
lock.lock(); |
753 |
try { |
754 |
return Arrays.copyOf(queue, size); |
755 |
} finally { |
756 |
lock.unlock(); |
757 |
} |
758 |
} |
759 |
|
760 |
/** |
761 |
* Returns an array containing all of the elements in this queue; the |
762 |
* runtime type of the returned array is that of the specified array. |
763 |
* The returned array elements are in no particular order. |
764 |
* If the queue fits in the specified array, it is returned therein. |
765 |
* Otherwise, a new array is allocated with the runtime type of the |
766 |
* specified array and the size of this queue. |
767 |
* |
768 |
* <p>If this queue fits in the specified array with room to spare |
769 |
* (i.e., the array has more elements than this queue), the element in |
770 |
* the array immediately following the end of the queue is set to |
771 |
* {@code null}. |
772 |
* |
773 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
774 |
* array-based and collection-based APIs. Further, this method allows |
775 |
* precise control over the runtime type of the output array, and may, |
776 |
* under certain circumstances, be used to save allocation costs. |
777 |
* |
778 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
779 |
* The following code can be used to dump the queue into a newly |
780 |
* allocated array of {@code String}: |
781 |
* |
782 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
783 |
* |
784 |
* Note that {@code toArray(new Object[0])} is identical in function to |
785 |
* {@code toArray()}. |
786 |
* |
787 |
* @param a the array into which the elements of the queue are to |
788 |
* be stored, if it is big enough; otherwise, a new array of the |
789 |
* same runtime type is allocated for this purpose |
790 |
* @return an array containing all of the elements in this queue |
791 |
* @throws ArrayStoreException if the runtime type of the specified array |
792 |
* is not a supertype of the runtime type of every element in |
793 |
* this queue |
794 |
* @throws NullPointerException if the specified array is null |
795 |
*/ |
796 |
public <T> T[] toArray(T[] a) { |
797 |
final ReentrantLock lock = this.lock; |
798 |
lock.lock(); |
799 |
try { |
800 |
int n = size; |
801 |
if (a.length < n) |
802 |
// Make a new array of a's runtime type, but my contents: |
803 |
return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
804 |
System.arraycopy(queue, 0, a, 0, n); |
805 |
if (a.length > n) |
806 |
a[n] = null; |
807 |
return a; |
808 |
} finally { |
809 |
lock.unlock(); |
810 |
} |
811 |
} |
812 |
|
813 |
/** |
814 |
* Returns an iterator over the elements in this queue. The |
815 |
* iterator does not return the elements in any particular order. |
816 |
* |
817 |
* <p>The returned iterator is |
818 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
819 |
* |
820 |
* @return an iterator over the elements in this queue |
821 |
*/ |
822 |
public Iterator<E> iterator() { |
823 |
return new Itr(toArray()); |
824 |
} |
825 |
|
826 |
/** |
827 |
* Snapshot iterator that works off copy of underlying q array. |
828 |
*/ |
829 |
final class Itr implements Iterator<E> { |
830 |
final Object[] array; // Array of all elements |
831 |
int cursor; // index of next element to return |
832 |
int lastRet = -1; // index of last element, or -1 if no such |
833 |
|
834 |
Itr(Object[] array) { |
835 |
this.array = array; |
836 |
} |
837 |
|
838 |
public boolean hasNext() { |
839 |
return cursor < array.length; |
840 |
} |
841 |
|
842 |
public E next() { |
843 |
if (cursor >= array.length) |
844 |
throw new NoSuchElementException(); |
845 |
return (E)array[lastRet = cursor++]; |
846 |
} |
847 |
|
848 |
public void remove() { |
849 |
if (lastRet < 0) |
850 |
throw new IllegalStateException(); |
851 |
removeEq(array[lastRet]); |
852 |
lastRet = -1; |
853 |
} |
854 |
|
855 |
public void forEachRemaining(Consumer<? super E> action) { |
856 |
Objects.requireNonNull(action); |
857 |
final Object[] es = array; |
858 |
int i; |
859 |
if ((i = cursor) < es.length) { |
860 |
lastRet = -1; |
861 |
cursor = es.length; |
862 |
for (; i < es.length; i++) |
863 |
action.accept((E) es[i]); |
864 |
lastRet = es.length - 1; |
865 |
} |
866 |
} |
867 |
} |
868 |
|
869 |
/** |
870 |
* Saves this queue to a stream (that is, serializes it). |
871 |
* |
872 |
* For compatibility with previous version of this class, elements |
873 |
* are first copied to a java.util.PriorityQueue, which is then |
874 |
* serialized. |
875 |
* |
876 |
* @param s the stream |
877 |
* @throws java.io.IOException if an I/O error occurs |
878 |
*/ |
879 |
private void writeObject(java.io.ObjectOutputStream s) |
880 |
throws java.io.IOException { |
881 |
lock.lock(); |
882 |
try { |
883 |
// avoid zero capacity argument |
884 |
q = new PriorityQueue<E>(Math.max(size, 1), comparator); |
885 |
q.addAll(this); |
886 |
s.defaultWriteObject(); |
887 |
} finally { |
888 |
q = null; |
889 |
lock.unlock(); |
890 |
} |
891 |
} |
892 |
|
893 |
/** |
894 |
* Reconstitutes this queue from a stream (that is, deserializes it). |
895 |
* @param s the stream |
896 |
* @throws ClassNotFoundException if the class of a serialized object |
897 |
* could not be found |
898 |
* @throws java.io.IOException if an I/O error occurs |
899 |
*/ |
900 |
private void readObject(java.io.ObjectInputStream s) |
901 |
throws java.io.IOException, ClassNotFoundException { |
902 |
try { |
903 |
s.defaultReadObject(); |
904 |
int sz = q.size(); |
905 |
SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, sz); |
906 |
this.queue = new Object[Math.max(1, sz)]; |
907 |
comparator = q.comparator(); |
908 |
addAll(q); |
909 |
} finally { |
910 |
q = null; |
911 |
} |
912 |
} |
913 |
|
914 |
/** |
915 |
* Immutable snapshot spliterator that binds to elements "late". |
916 |
*/ |
917 |
final class PBQSpliterator implements Spliterator<E> { |
918 |
Object[] array; // null until late-bound-initialized |
919 |
int index; |
920 |
int fence; |
921 |
|
922 |
PBQSpliterator() {} |
923 |
|
924 |
PBQSpliterator(Object[] array, int index, int fence) { |
925 |
this.array = array; |
926 |
this.index = index; |
927 |
this.fence = fence; |
928 |
} |
929 |
|
930 |
private int getFence() { |
931 |
if (array == null) |
932 |
fence = (array = toArray()).length; |
933 |
return fence; |
934 |
} |
935 |
|
936 |
public PBQSpliterator trySplit() { |
937 |
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; |
938 |
return (lo >= mid) ? null : |
939 |
new PBQSpliterator(array, lo, index = mid); |
940 |
} |
941 |
|
942 |
public void forEachRemaining(Consumer<? super E> action) { |
943 |
Objects.requireNonNull(action); |
944 |
final int hi = getFence(), lo = index; |
945 |
final Object[] es = array; |
946 |
index = hi; // ensure exhaustion |
947 |
for (int i = lo; i < hi; i++) |
948 |
action.accept((E) es[i]); |
949 |
} |
950 |
|
951 |
public boolean tryAdvance(Consumer<? super E> action) { |
952 |
Objects.requireNonNull(action); |
953 |
if (getFence() > index && index >= 0) { |
954 |
action.accept((E) array[index++]); |
955 |
return true; |
956 |
} |
957 |
return false; |
958 |
} |
959 |
|
960 |
public long estimateSize() { return getFence() - index; } |
961 |
|
962 |
public int characteristics() { |
963 |
return (Spliterator.NONNULL | |
964 |
Spliterator.SIZED | |
965 |
Spliterator.SUBSIZED); |
966 |
} |
967 |
} |
968 |
|
969 |
/** |
970 |
* Returns a {@link Spliterator} over the elements in this queue. |
971 |
* The spliterator does not traverse elements in any particular order |
972 |
* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported). |
973 |
* |
974 |
* <p>The returned spliterator is |
975 |
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
976 |
* |
977 |
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and |
978 |
* {@link Spliterator#NONNULL}. |
979 |
* |
980 |
* @implNote |
981 |
* The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}. |
982 |
* |
983 |
* @return a {@code Spliterator} over the elements in this queue |
984 |
* @since 1.8 |
985 |
*/ |
986 |
public Spliterator<E> spliterator() { |
987 |
return new PBQSpliterator(); |
988 |
} |
989 |
|
990 |
/** |
991 |
* @throws NullPointerException {@inheritDoc} |
992 |
*/ |
993 |
public void forEach(Consumer<? super E> action) { |
994 |
Objects.requireNonNull(action); |
995 |
final ReentrantLock lock = this.lock; |
996 |
lock.lock(); |
997 |
try { |
998 |
final Object[] es = queue; |
999 |
for (int i = 0, n = size; i < n; i++) |
1000 |
action.accept((E) es[i]); |
1001 |
} finally { |
1002 |
lock.unlock(); |
1003 |
} |
1004 |
} |
1005 |
|
1006 |
// VarHandle mechanics |
1007 |
private static final VarHandle ALLOCATIONSPINLOCK; |
1008 |
static { |
1009 |
try { |
1010 |
MethodHandles.Lookup l = MethodHandles.lookup(); |
1011 |
ALLOCATIONSPINLOCK = l.findVarHandle(PriorityBlockingQueue.class, |
1012 |
"allocationSpinLock", |
1013 |
int.class); |
1014 |
} catch (ReflectiveOperationException e) { |
1015 |
throw new ExceptionInInitializerError(e); |
1016 |
} |
1017 |
} |
1018 |
} |