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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.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReentrantLock; |
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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.Collections; |
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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.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.stream.Stream; |
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import java.util.function.Consumer; |
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|
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/** |
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* An unbounded {@linkplain BlockingQueue blocking queue} that uses |
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* 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 |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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* Iterator} interfaces. The Iterator provided in method {@link |
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* #iterator()} is <em>not</em> guaranteed to traverse the elements of |
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* the PriorityBlockingQueue in any particular order. If you need |
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* ordered traversal, consider using |
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* {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo} |
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* can be used to <em>remove</em> some or all elements in priority |
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* order and 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. |
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* |
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* <pre> {@code |
55 |
* class FIFOEntry<E extends Comparable<? super E>> |
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* implements Comparable<FIFOEntry<E>> { |
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* static final AtomicLong seq = new AtomicLong(0); |
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* final long seqNum; |
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* final E entry; |
60 |
* public FIFOEntry(E entry) { |
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* seqNum = seq.getAndIncrement(); |
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* this.entry = entry; |
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* } |
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* public E getEntry() { return entry; } |
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* public int compareTo(FIFOEntry<E> other) { |
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* int res = entry.compareTo(other.entry); |
67 |
* if (res == 0 && other.entry != this.entry) |
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* res = (seqNum < other.seqNum ? -1 : 1); |
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* return res; |
70 |
* } |
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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}/../technotes/guides/collections/index.html"> |
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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 collection |
80 |
*/ |
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@SuppressWarnings("unchecked") |
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public class PriorityBlockingQueue<E> extends AbstractQueue<E> |
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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 |
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* operations protected with a single lock. However, allocation |
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* during resizing uses a simple spinlock (used only while not |
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* 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 |
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* build-up. The need to back away from lock during allocation |
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* makes it impossible to simply wrap delegated |
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* java.util.PriorityQueue operations within a lock, as was done |
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* in a previous version of this class. To maintain |
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* interoperability, a plain PriorityQueue is still used during |
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* serialization, which maintains compatibility at the expense of |
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* transiently doubling overhead. |
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*/ |
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|
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/** |
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* Default array capacity. |
104 |
*/ |
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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. |
110 |
* Attempts to allocate larger arrays may result in |
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* OutOfMemoryError: Requested array size exceeds VM limit |
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*/ |
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private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; |
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|
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/** |
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* 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 |
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* 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 |
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* heap and each descendant d of n, n <= d. The element with the |
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* lowest value is in queue[0], assuming the queue is nonempty. |
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*/ |
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private transient Object[] queue; |
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|
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/** |
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* The number of elements in the priority queue. |
127 |
*/ |
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private transient int size; |
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|
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/** |
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* The comparator, or null if priority queue uses elements' |
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* natural ordering. |
133 |
*/ |
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private transient Comparator<? super E> comparator; |
135 |
|
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/** |
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* Lock used for all public operations |
138 |
*/ |
139 |
private final ReentrantLock lock; |
140 |
|
141 |
/** |
142 |
* Condition for blocking when empty |
143 |
*/ |
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private final Condition notEmpty; |
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|
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/** |
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* Spinlock for allocation, acquired via CAS. |
148 |
*/ |
149 |
private transient volatile int allocationSpinLock; |
150 |
|
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/** |
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* A plain PriorityQueue used only for serialization, |
153 |
* to maintain compatibility with previous versions |
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* of this class. Non-null only during serialization/deserialization. |
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*/ |
156 |
private PriorityQueue<E> q; |
157 |
|
158 |
/** |
159 |
* Creates a {@code PriorityBlockingQueue} with the default |
160 |
* initial capacity (11) that orders its elements according to |
161 |
* their {@linkplain Comparable natural ordering}. |
162 |
*/ |
163 |
public PriorityBlockingQueue() { |
164 |
this(DEFAULT_INITIAL_CAPACITY, null); |
165 |
} |
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|
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/** |
168 |
* Creates a {@code PriorityBlockingQueue} with the specified |
169 |
* initial capacity that orders its elements according to their |
170 |
* {@linkplain Comparable natural ordering}. |
171 |
* |
172 |
* @param initialCapacity the initial capacity for this priority queue |
173 |
* @throws IllegalArgumentException if {@code initialCapacity} is less |
174 |
* than 1 |
175 |
*/ |
176 |
public PriorityBlockingQueue(int initialCapacity) { |
177 |
this(initialCapacity, null); |
178 |
} |
179 |
|
180 |
/** |
181 |
* Creates a {@code PriorityBlockingQueue} with the specified initial |
182 |
* capacity that orders its elements according to the specified |
183 |
* comparator. |
184 |
* |
185 |
* @param initialCapacity the initial capacity for this priority queue |
186 |
* @param comparator the comparator that will be used to order this |
187 |
* priority queue. If {@code null}, the {@linkplain Comparable |
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* natural ordering} of the elements will be used. |
189 |
* @throws IllegalArgumentException if {@code initialCapacity} is less |
190 |
* than 1 |
191 |
*/ |
192 |
public PriorityBlockingQueue(int initialCapacity, |
193 |
Comparator<? super E> comparator) { |
194 |
if (initialCapacity < 1) |
195 |
throw new IllegalArgumentException(); |
196 |
this.lock = new ReentrantLock(); |
197 |
this.notEmpty = lock.newCondition(); |
198 |
this.comparator = comparator; |
199 |
this.queue = new Object[initialCapacity]; |
200 |
} |
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|
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/** |
203 |
* Creates a {@code PriorityBlockingQueue} with the default |
204 |
* initial capacity that orders its elements according to the |
205 |
* specified comparator. |
206 |
* |
207 |
* @param comparator the comparator that will be used to order this |
208 |
* priority queue. If {@code null}, the {@linkplain Comparable |
209 |
* natural ordering} of the elements will be used. |
210 |
* @since 1.8 |
211 |
*/ |
212 |
public PriorityBlockingQueue(Comparator<? super E> comparator) { |
213 |
this(DEFAULT_INITIAL_CAPACITY, comparator); |
214 |
} |
215 |
|
216 |
/** |
217 |
* Creates a {@code PriorityBlockingQueue} containing the elements |
218 |
* in the specified collection. If the specified collection is a |
219 |
* {@link SortedSet} or a {@link PriorityQueue}, this |
220 |
* priority queue will be ordered according to the same ordering. |
221 |
* Otherwise, this priority queue will be ordered according to the |
222 |
* {@linkplain Comparable natural ordering} of its elements. |
223 |
* |
224 |
* @param c the collection whose elements are to be placed |
225 |
* into this priority queue |
226 |
* @throws ClassCastException if elements of the specified collection |
227 |
* cannot be compared to one another according to the priority |
228 |
* queue's ordering |
229 |
* @throws NullPointerException if the specified collection or any |
230 |
* of its elements are null |
231 |
*/ |
232 |
public PriorityBlockingQueue(Collection<? extends E> c) { |
233 |
this.lock = new ReentrantLock(); |
234 |
this.notEmpty = lock.newCondition(); |
235 |
boolean heapify = true; // true if not known to be in heap order |
236 |
boolean screen = true; // true if must screen for nulls |
237 |
if (c instanceof SortedSet<?>) { |
238 |
SortedSet<? extends E> ss = (SortedSet<? extends E>) c; |
239 |
this.comparator = (Comparator<? super E>) ss.comparator(); |
240 |
heapify = false; |
241 |
} |
242 |
else if (c instanceof PriorityBlockingQueue<?>) { |
243 |
PriorityBlockingQueue<? extends E> pq = |
244 |
(PriorityBlockingQueue<? extends E>) c; |
245 |
this.comparator = (Comparator<? super E>) pq.comparator(); |
246 |
screen = false; |
247 |
if (pq.getClass() == PriorityBlockingQueue.class) // exact match |
248 |
heapify = false; |
249 |
} |
250 |
Object[] a = c.toArray(); |
251 |
int n = a.length; |
252 |
// If c.toArray incorrectly doesn't return Object[], copy it. |
253 |
if (a.getClass() != Object[].class) |
254 |
a = Arrays.copyOf(a, n, Object[].class); |
255 |
if (screen && (n == 1 || this.comparator != null)) { |
256 |
for (int i = 0; i < n; ++i) |
257 |
if (a[i] == null) |
258 |
throw new NullPointerException(); |
259 |
} |
260 |
this.queue = a; |
261 |
this.size = n; |
262 |
if (heapify) |
263 |
heapify(); |
264 |
} |
265 |
|
266 |
/** |
267 |
* Tries to grow array to accommodate at least one more element |
268 |
* (but normally expand by about 50%), giving up (allowing retry) |
269 |
* on contention (which we expect to be rare). Call only while |
270 |
* holding lock. |
271 |
* |
272 |
* @param array the heap array |
273 |
* @param oldCap the length of the array |
274 |
*/ |
275 |
private void tryGrow(Object[] array, int oldCap) { |
276 |
lock.unlock(); // must release and then re-acquire main lock |
277 |
Object[] newArray = null; |
278 |
if (allocationSpinLock == 0 && |
279 |
UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset, |
280 |
0, 1)) { |
281 |
try { |
282 |
int newCap = oldCap + ((oldCap < 64) ? |
283 |
(oldCap + 2) : // grow faster if small |
284 |
(oldCap >> 1)); |
285 |
if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow |
286 |
int minCap = oldCap + 1; |
287 |
if (minCap < 0 || minCap > MAX_ARRAY_SIZE) |
288 |
throw new OutOfMemoryError(); |
289 |
newCap = MAX_ARRAY_SIZE; |
290 |
} |
291 |
if (newCap > oldCap && queue == array) |
292 |
newArray = new Object[newCap]; |
293 |
} finally { |
294 |
allocationSpinLock = 0; |
295 |
} |
296 |
} |
297 |
if (newArray == null) // back off if another thread is allocating |
298 |
Thread.yield(); |
299 |
lock.lock(); |
300 |
if (newArray != null && queue == array) { |
301 |
queue = newArray; |
302 |
System.arraycopy(array, 0, newArray, 0, oldCap); |
303 |
} |
304 |
} |
305 |
|
306 |
/** |
307 |
* Mechanics for poll(). Call only while holding lock. |
308 |
*/ |
309 |
private E dequeue() { |
310 |
int n = size - 1; |
311 |
if (n < 0) |
312 |
return null; |
313 |
else { |
314 |
Object[] array = queue; |
315 |
E result = (E) array[0]; |
316 |
E x = (E) array[n]; |
317 |
array[n] = null; |
318 |
Comparator<? super E> cmp = comparator; |
319 |
if (cmp == null) |
320 |
siftDownComparable(0, x, array, n); |
321 |
else |
322 |
siftDownUsingComparator(0, x, array, n, cmp); |
323 |
size = n; |
324 |
return result; |
325 |
} |
326 |
} |
327 |
|
328 |
/** |
329 |
* Inserts item x at position k, maintaining heap invariant by |
330 |
* promoting x up the tree until it is greater than or equal to |
331 |
* its parent, or is the root. |
332 |
* |
333 |
* To simplify and speed up coercions and comparisons. the |
334 |
* Comparable and Comparator versions are separated into different |
335 |
* methods that are otherwise identical. (Similarly for siftDown.) |
336 |
* These methods are static, with heap state as arguments, to |
337 |
* simplify use in light of possible comparator exceptions. |
338 |
* |
339 |
* @param k the position to fill |
340 |
* @param x the item to insert |
341 |
* @param array the heap array |
342 |
*/ |
343 |
private static <T> void siftUpComparable(int k, T x, Object[] array) { |
344 |
Comparable<? super T> key = (Comparable<? super T>) x; |
345 |
while (k > 0) { |
346 |
int parent = (k - 1) >>> 1; |
347 |
Object e = array[parent]; |
348 |
if (key.compareTo((T) e) >= 0) |
349 |
break; |
350 |
array[k] = e; |
351 |
k = parent; |
352 |
} |
353 |
array[k] = key; |
354 |
} |
355 |
|
356 |
private static <T> void siftUpUsingComparator(int k, T x, Object[] array, |
357 |
Comparator<? super T> cmp) { |
358 |
while (k > 0) { |
359 |
int parent = (k - 1) >>> 1; |
360 |
Object e = array[parent]; |
361 |
if (cmp.compare(x, (T) e) >= 0) |
362 |
break; |
363 |
array[k] = e; |
364 |
k = parent; |
365 |
} |
366 |
array[k] = x; |
367 |
} |
368 |
|
369 |
/** |
370 |
* Inserts item x at position k, maintaining heap invariant by |
371 |
* demoting x down the tree repeatedly until it is less than or |
372 |
* equal to its children or is a leaf. |
373 |
* |
374 |
* @param k the position to fill |
375 |
* @param x the item to insert |
376 |
* @param array the heap array |
377 |
* @param n heap size |
378 |
*/ |
379 |
private static <T> void siftDownComparable(int k, T x, Object[] array, |
380 |
int n) { |
381 |
if (n > 0) { |
382 |
Comparable<? super T> key = (Comparable<? super T>)x; |
383 |
int half = n >>> 1; // loop while a non-leaf |
384 |
while (k < half) { |
385 |
int child = (k << 1) + 1; // assume left child is least |
386 |
Object c = array[child]; |
387 |
int right = child + 1; |
388 |
if (right < n && |
389 |
((Comparable<? super T>) c).compareTo((T) array[right]) > 0) |
390 |
c = array[child = right]; |
391 |
if (key.compareTo((T) c) <= 0) |
392 |
break; |
393 |
array[k] = c; |
394 |
k = child; |
395 |
} |
396 |
array[k] = key; |
397 |
} |
398 |
} |
399 |
|
400 |
private static <T> void siftDownUsingComparator(int k, T x, Object[] array, |
401 |
int n, |
402 |
Comparator<? super T> cmp) { |
403 |
if (n > 0) { |
404 |
int half = n >>> 1; |
405 |
while (k < half) { |
406 |
int child = (k << 1) + 1; |
407 |
Object c = array[child]; |
408 |
int right = child + 1; |
409 |
if (right < n && cmp.compare((T) c, (T) array[right]) > 0) |
410 |
c = array[child = right]; |
411 |
if (cmp.compare(x, (T) c) <= 0) |
412 |
break; |
413 |
array[k] = c; |
414 |
k = child; |
415 |
} |
416 |
array[k] = x; |
417 |
} |
418 |
} |
419 |
|
420 |
/** |
421 |
* Establishes the heap invariant (described above) in the entire tree, |
422 |
* assuming nothing about the order of the elements prior to the call. |
423 |
*/ |
424 |
private void heapify() { |
425 |
Object[] array = queue; |
426 |
int n = size; |
427 |
int half = (n >>> 1) - 1; |
428 |
Comparator<? super E> cmp = comparator; |
429 |
if (cmp == null) { |
430 |
for (int i = half; i >= 0; i--) |
431 |
siftDownComparable(i, (E) array[i], array, n); |
432 |
} |
433 |
else { |
434 |
for (int i = half; i >= 0; i--) |
435 |
siftDownUsingComparator(i, (E) array[i], array, n, cmp); |
436 |
} |
437 |
} |
438 |
|
439 |
/** |
440 |
* Inserts the specified element into this priority queue. |
441 |
* |
442 |
* @param e the element to add |
443 |
* @return {@code true} (as specified by {@link Collection#add}) |
444 |
* @throws ClassCastException if the specified element cannot be compared |
445 |
* with elements currently in the priority queue according to the |
446 |
* priority queue's ordering |
447 |
* @throws NullPointerException if the specified element is null |
448 |
*/ |
449 |
public boolean add(E e) { |
450 |
return offer(e); |
451 |
} |
452 |
|
453 |
/** |
454 |
* Inserts the specified element into this priority queue. |
455 |
* As the queue is unbounded, this method will never return {@code false}. |
456 |
* |
457 |
* @param e the element to add |
458 |
* @return {@code true} (as specified by {@link Queue#offer}) |
459 |
* @throws ClassCastException if the specified element cannot be compared |
460 |
* with elements currently in the priority queue according to the |
461 |
* priority queue's ordering |
462 |
* @throws NullPointerException if the specified element is null |
463 |
*/ |
464 |
public boolean offer(E e) { |
465 |
if (e == null) |
466 |
throw new NullPointerException(); |
467 |
final ReentrantLock lock = this.lock; |
468 |
lock.lock(); |
469 |
int n, cap; |
470 |
Object[] array; |
471 |
while ((n = size) >= (cap = (array = queue).length)) |
472 |
tryGrow(array, cap); |
473 |
try { |
474 |
Comparator<? super E> cmp = comparator; |
475 |
if (cmp == null) |
476 |
siftUpComparable(n, e, array); |
477 |
else |
478 |
siftUpUsingComparator(n, e, array, cmp); |
479 |
size = n + 1; |
480 |
notEmpty.signal(); |
481 |
} finally { |
482 |
lock.unlock(); |
483 |
} |
484 |
return true; |
485 |
} |
486 |
|
487 |
/** |
488 |
* Inserts the specified element into this priority queue. |
489 |
* As the queue is unbounded, this method will never block. |
490 |
* |
491 |
* @param e the element to add |
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 void put(E e) { |
498 |
offer(e); // never need to block |
499 |
} |
500 |
|
501 |
/** |
502 |
* Inserts the specified element into this priority queue. |
503 |
* As the queue is unbounded, this method will never block or |
504 |
* return {@code false}. |
505 |
* |
506 |
* @param e the element to add |
507 |
* @param timeout This parameter is ignored as the method never blocks |
508 |
* @param unit This parameter is ignored as the method never blocks |
509 |
* @return {@code true} (as specified by |
510 |
* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
511 |
* @throws ClassCastException if the specified element cannot be compared |
512 |
* with elements currently in the priority queue according to the |
513 |
* priority queue's ordering |
514 |
* @throws NullPointerException if the specified element is null |
515 |
*/ |
516 |
public boolean offer(E e, long timeout, TimeUnit unit) { |
517 |
return offer(e); // never need to block |
518 |
} |
519 |
|
520 |
public E poll() { |
521 |
final ReentrantLock lock = this.lock; |
522 |
lock.lock(); |
523 |
try { |
524 |
return dequeue(); |
525 |
} finally { |
526 |
lock.unlock(); |
527 |
} |
528 |
} |
529 |
|
530 |
public E take() throws InterruptedException { |
531 |
final ReentrantLock lock = this.lock; |
532 |
lock.lockInterruptibly(); |
533 |
E result; |
534 |
try { |
535 |
while ( (result = dequeue()) == null) |
536 |
notEmpty.await(); |
537 |
} finally { |
538 |
lock.unlock(); |
539 |
} |
540 |
return result; |
541 |
} |
542 |
|
543 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
544 |
long nanos = unit.toNanos(timeout); |
545 |
final ReentrantLock lock = this.lock; |
546 |
lock.lockInterruptibly(); |
547 |
E result; |
548 |
try { |
549 |
while ( (result = dequeue()) == null && nanos > 0) |
550 |
nanos = notEmpty.awaitNanos(nanos); |
551 |
} finally { |
552 |
lock.unlock(); |
553 |
} |
554 |
return result; |
555 |
} |
556 |
|
557 |
public E peek() { |
558 |
final ReentrantLock lock = this.lock; |
559 |
lock.lock(); |
560 |
try { |
561 |
return (size == 0) ? null : (E) queue[0]; |
562 |
} finally { |
563 |
lock.unlock(); |
564 |
} |
565 |
} |
566 |
|
567 |
/** |
568 |
* Returns the comparator used to order the elements in this queue, |
569 |
* or {@code null} if this queue uses the {@linkplain Comparable |
570 |
* natural ordering} of its elements. |
571 |
* |
572 |
* @return the comparator used to order the elements in this queue, |
573 |
* or {@code null} if this queue uses the natural |
574 |
* ordering of its elements |
575 |
*/ |
576 |
public Comparator<? super E> comparator() { |
577 |
return comparator; |
578 |
} |
579 |
|
580 |
public int size() { |
581 |
final ReentrantLock lock = this.lock; |
582 |
lock.lock(); |
583 |
try { |
584 |
return size; |
585 |
} finally { |
586 |
lock.unlock(); |
587 |
} |
588 |
} |
589 |
|
590 |
/** |
591 |
* Always returns {@code Integer.MAX_VALUE} because |
592 |
* a {@code PriorityBlockingQueue} is not capacity constrained. |
593 |
* @return {@code Integer.MAX_VALUE} always |
594 |
*/ |
595 |
public int remainingCapacity() { |
596 |
return Integer.MAX_VALUE; |
597 |
} |
598 |
|
599 |
private int indexOf(Object o) { |
600 |
if (o != null) { |
601 |
Object[] array = queue; |
602 |
int n = size; |
603 |
for (int i = 0; i < n; i++) |
604 |
if (o.equals(array[i])) |
605 |
return i; |
606 |
} |
607 |
return -1; |
608 |
} |
609 |
|
610 |
/** |
611 |
* Removes the ith element from queue. |
612 |
*/ |
613 |
private void removeAt(int i) { |
614 |
Object[] array = queue; |
615 |
int n = size - 1; |
616 |
if (n == i) // removed last element |
617 |
array[i] = null; |
618 |
else { |
619 |
E moved = (E) array[n]; |
620 |
array[n] = null; |
621 |
Comparator<? super E> cmp = comparator; |
622 |
if (cmp == null) |
623 |
siftDownComparable(i, moved, array, n); |
624 |
else |
625 |
siftDownUsingComparator(i, moved, array, n, cmp); |
626 |
if (array[i] == moved) { |
627 |
if (cmp == null) |
628 |
siftUpComparable(i, moved, array); |
629 |
else |
630 |
siftUpUsingComparator(i, moved, array, cmp); |
631 |
} |
632 |
} |
633 |
size = n; |
634 |
} |
635 |
|
636 |
/** |
637 |
* Removes a single instance of the specified element from this queue, |
638 |
* if it is present. More formally, removes an element {@code e} such |
639 |
* that {@code o.equals(e)}, if this queue contains one or more such |
640 |
* elements. Returns {@code true} if and only if this queue contained |
641 |
* the specified element (or equivalently, if this queue changed as a |
642 |
* result of the call). |
643 |
* |
644 |
* @param o element to be removed from this queue, if present |
645 |
* @return {@code true} if this queue changed as a result of the call |
646 |
*/ |
647 |
public boolean remove(Object o) { |
648 |
final ReentrantLock lock = this.lock; |
649 |
lock.lock(); |
650 |
try { |
651 |
int i = indexOf(o); |
652 |
if (i == -1) |
653 |
return false; |
654 |
removeAt(i); |
655 |
return true; |
656 |
} finally { |
657 |
lock.unlock(); |
658 |
} |
659 |
} |
660 |
|
661 |
/** |
662 |
* Identity-based version for use in Itr.remove |
663 |
*/ |
664 |
void removeEQ(Object o) { |
665 |
final ReentrantLock lock = this.lock; |
666 |
lock.lock(); |
667 |
try { |
668 |
Object[] array = queue; |
669 |
for (int i = 0, n = size; i < n; i++) { |
670 |
if (o == array[i]) { |
671 |
removeAt(i); |
672 |
break; |
673 |
} |
674 |
} |
675 |
} finally { |
676 |
lock.unlock(); |
677 |
} |
678 |
} |
679 |
|
680 |
/** |
681 |
* Returns {@code true} if this queue contains the specified element. |
682 |
* More formally, returns {@code true} if and only if this queue contains |
683 |
* at least one element {@code e} such that {@code o.equals(e)}. |
684 |
* |
685 |
* @param o object to be checked for containment in this queue |
686 |
* @return {@code true} if this queue contains the specified element |
687 |
*/ |
688 |
public boolean contains(Object o) { |
689 |
final ReentrantLock lock = this.lock; |
690 |
lock.lock(); |
691 |
try { |
692 |
return indexOf(o) != -1; |
693 |
} finally { |
694 |
lock.unlock(); |
695 |
} |
696 |
} |
697 |
|
698 |
/** |
699 |
* Returns an array containing all of the elements in this queue. |
700 |
* The returned array elements are in no particular order. |
701 |
* |
702 |
* <p>The returned array will be "safe" in that no references to it are |
703 |
* maintained by this queue. (In other words, this method must allocate |
704 |
* a new array). The caller is thus free to modify the returned array. |
705 |
* |
706 |
* <p>This method acts as bridge between array-based and collection-based |
707 |
* APIs. |
708 |
* |
709 |
* @return an array containing all of the elements in this queue |
710 |
*/ |
711 |
public Object[] toArray() { |
712 |
final ReentrantLock lock = this.lock; |
713 |
lock.lock(); |
714 |
try { |
715 |
return Arrays.copyOf(queue, size); |
716 |
} finally { |
717 |
lock.unlock(); |
718 |
} |
719 |
} |
720 |
|
721 |
public String toString() { |
722 |
final ReentrantLock lock = this.lock; |
723 |
lock.lock(); |
724 |
try { |
725 |
int n = size; |
726 |
if (n == 0) |
727 |
return "[]"; |
728 |
StringBuilder sb = new StringBuilder(); |
729 |
sb.append('['); |
730 |
for (int i = 0; i < n; ++i) { |
731 |
Object e = queue[i]; |
732 |
sb.append(e == this ? "(this Collection)" : e); |
733 |
if (i != n - 1) |
734 |
sb.append(',').append(' '); |
735 |
} |
736 |
return sb.append(']').toString(); |
737 |
} finally { |
738 |
lock.unlock(); |
739 |
} |
740 |
} |
741 |
|
742 |
/** |
743 |
* @throws UnsupportedOperationException {@inheritDoc} |
744 |
* @throws ClassCastException {@inheritDoc} |
745 |
* @throws NullPointerException {@inheritDoc} |
746 |
* @throws IllegalArgumentException {@inheritDoc} |
747 |
*/ |
748 |
public int drainTo(Collection<? super E> c) { |
749 |
return drainTo(c, Integer.MAX_VALUE); |
750 |
} |
751 |
|
752 |
/** |
753 |
* @throws UnsupportedOperationException {@inheritDoc} |
754 |
* @throws ClassCastException {@inheritDoc} |
755 |
* @throws NullPointerException {@inheritDoc} |
756 |
* @throws IllegalArgumentException {@inheritDoc} |
757 |
*/ |
758 |
public int drainTo(Collection<? super E> c, int maxElements) { |
759 |
if (c == null) |
760 |
throw new NullPointerException(); |
761 |
if (c == this) |
762 |
throw new IllegalArgumentException(); |
763 |
if (maxElements <= 0) |
764 |
return 0; |
765 |
final ReentrantLock lock = this.lock; |
766 |
lock.lock(); |
767 |
try { |
768 |
int n = Math.min(size, maxElements); |
769 |
for (int i = 0; i < n; i++) { |
770 |
c.add((E) queue[0]); // In this order, in case add() throws. |
771 |
dequeue(); |
772 |
} |
773 |
return n; |
774 |
} finally { |
775 |
lock.unlock(); |
776 |
} |
777 |
} |
778 |
|
779 |
/** |
780 |
* Atomically removes all of the elements from this queue. |
781 |
* The queue will be empty after this call returns. |
782 |
*/ |
783 |
public void clear() { |
784 |
final ReentrantLock lock = this.lock; |
785 |
lock.lock(); |
786 |
try { |
787 |
Object[] array = queue; |
788 |
int n = size; |
789 |
size = 0; |
790 |
for (int i = 0; i < n; i++) |
791 |
array[i] = null; |
792 |
} finally { |
793 |
lock.unlock(); |
794 |
} |
795 |
} |
796 |
|
797 |
/** |
798 |
* Returns an array containing all of the elements in this queue; the |
799 |
* runtime type of the returned array is that of the specified array. |
800 |
* The returned array elements are in no particular order. |
801 |
* If the queue fits in the specified array, it is returned therein. |
802 |
* Otherwise, a new array is allocated with the runtime type of the |
803 |
* specified array and the size of this queue. |
804 |
* |
805 |
* <p>If this queue fits in the specified array with room to spare |
806 |
* (i.e., the array has more elements than this queue), the element in |
807 |
* the array immediately following the end of the queue is set to |
808 |
* {@code null}. |
809 |
* |
810 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
811 |
* array-based and collection-based APIs. Further, this method allows |
812 |
* precise control over the runtime type of the output array, and may, |
813 |
* under certain circumstances, be used to save allocation costs. |
814 |
* |
815 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
816 |
* The following code can be used to dump the queue into a newly |
817 |
* allocated array of {@code String}: |
818 |
* |
819 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
820 |
* |
821 |
* Note that {@code toArray(new Object[0])} is identical in function to |
822 |
* {@code toArray()}. |
823 |
* |
824 |
* @param a the array into which the elements of the queue are to |
825 |
* be stored, if it is big enough; otherwise, a new array of the |
826 |
* same runtime type is allocated for this purpose |
827 |
* @return an array containing all of the elements in this queue |
828 |
* @throws ArrayStoreException if the runtime type of the specified array |
829 |
* is not a supertype of the runtime type of every element in |
830 |
* this queue |
831 |
* @throws NullPointerException if the specified array is null |
832 |
*/ |
833 |
public <T> T[] toArray(T[] a) { |
834 |
final ReentrantLock lock = this.lock; |
835 |
lock.lock(); |
836 |
try { |
837 |
int n = size; |
838 |
if (a.length < n) |
839 |
// Make a new array of a's runtime type, but my contents: |
840 |
return (T[]) Arrays.copyOf(queue, size, a.getClass()); |
841 |
System.arraycopy(queue, 0, a, 0, n); |
842 |
if (a.length > n) |
843 |
a[n] = null; |
844 |
return a; |
845 |
} finally { |
846 |
lock.unlock(); |
847 |
} |
848 |
} |
849 |
|
850 |
/** |
851 |
* Returns an iterator over the elements in this queue. The |
852 |
* iterator does not return the elements in any particular order. |
853 |
* |
854 |
* <p>The returned iterator is a "weakly consistent" iterator that |
855 |
* will never throw {@link java.util.ConcurrentModificationException |
856 |
* ConcurrentModificationException}, and guarantees to traverse |
857 |
* elements as they existed upon construction of the iterator, and |
858 |
* may (but is not guaranteed to) reflect any modifications |
859 |
* subsequent to construction. |
860 |
* |
861 |
* @return an iterator over the elements in this queue |
862 |
*/ |
863 |
public Iterator<E> iterator() { |
864 |
return new Itr(toArray()); |
865 |
} |
866 |
|
867 |
/** |
868 |
* Snapshot iterator that works off copy of underlying q array. |
869 |
*/ |
870 |
final class Itr implements Iterator<E> { |
871 |
final Object[] array; // Array of all elements |
872 |
int cursor; // index of next element to return |
873 |
int lastRet; // index of last element, or -1 if no such |
874 |
|
875 |
Itr(Object[] array) { |
876 |
lastRet = -1; |
877 |
this.array = array; |
878 |
} |
879 |
|
880 |
public boolean hasNext() { |
881 |
return cursor < array.length; |
882 |
} |
883 |
|
884 |
public E next() { |
885 |
if (cursor >= array.length) |
886 |
throw new NoSuchElementException(); |
887 |
lastRet = cursor; |
888 |
return (E)array[cursor++]; |
889 |
} |
890 |
|
891 |
public void remove() { |
892 |
if (lastRet < 0) |
893 |
throw new IllegalStateException(); |
894 |
removeEQ(array[lastRet]); |
895 |
lastRet = -1; |
896 |
} |
897 |
} |
898 |
|
899 |
/** |
900 |
* Saves this queue to a stream (that is, serializes it). |
901 |
* |
902 |
* For compatibility with previous version of this class, elements |
903 |
* are first copied to a java.util.PriorityQueue, which is then |
904 |
* serialized. |
905 |
* |
906 |
* @param s the stream |
907 |
* @throws java.io.IOException if an I/O error occurs |
908 |
*/ |
909 |
private void writeObject(java.io.ObjectOutputStream s) |
910 |
throws java.io.IOException { |
911 |
lock.lock(); |
912 |
try { |
913 |
// avoid zero capacity argument |
914 |
q = new PriorityQueue<E>(Math.max(size, 1), comparator); |
915 |
q.addAll(this); |
916 |
s.defaultWriteObject(); |
917 |
} finally { |
918 |
q = null; |
919 |
lock.unlock(); |
920 |
} |
921 |
} |
922 |
|
923 |
/** |
924 |
* Reconstitutes this queue from a stream (that is, deserializes it). |
925 |
* @param s the stream |
926 |
* @throws ClassNotFoundException if the class of a serialized object |
927 |
* could not be found |
928 |
* @throws java.io.IOException if an I/O error occurs |
929 |
*/ |
930 |
private void readObject(java.io.ObjectInputStream s) |
931 |
throws java.io.IOException, ClassNotFoundException { |
932 |
try { |
933 |
s.defaultReadObject(); |
934 |
this.queue = new Object[q.size()]; |
935 |
comparator = q.comparator(); |
936 |
addAll(q); |
937 |
} finally { |
938 |
q = null; |
939 |
} |
940 |
} |
941 |
|
942 |
// Similar to Collections.ArraySnapshotSpliterator but avoids |
943 |
// commitment to toArray until needed |
944 |
static final class PBQSpliterator<E> implements Spliterator<E> { |
945 |
final PriorityBlockingQueue<E> queue; |
946 |
Object[] array; |
947 |
int index; |
948 |
int fence; |
949 |
|
950 |
PBQSpliterator(PriorityBlockingQueue<E> queue, Object[] array, |
951 |
int index, int fence) { |
952 |
this.queue = queue; |
953 |
this.array = array; |
954 |
this.index = index; |
955 |
this.fence = fence; |
956 |
} |
957 |
|
958 |
final int getFence() { |
959 |
int hi; |
960 |
if ((hi = fence) < 0) |
961 |
hi = fence = (array = queue.toArray()).length; |
962 |
return hi; |
963 |
} |
964 |
|
965 |
public Spliterator<E> trySplit() { |
966 |
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; |
967 |
return (lo >= mid) ? null : |
968 |
new PBQSpliterator<E>(queue, array, lo, index = mid); |
969 |
} |
970 |
|
971 |
@SuppressWarnings("unchecked") |
972 |
public void forEachRemaining(Consumer<? super E> action) { |
973 |
Object[] a; int i, hi; // hoist accesses and checks from loop |
974 |
if (action == null) |
975 |
throw new NullPointerException(); |
976 |
if ((a = array) == null) |
977 |
fence = (a = queue.toArray()).length; |
978 |
if ((hi = fence) <= a.length && |
979 |
(i = index) >= 0 && i < (index = hi)) { |
980 |
do { action.accept((E)a[i]); } while (++i < hi); |
981 |
} |
982 |
} |
983 |
|
984 |
public boolean tryAdvance(Consumer<? super E> action) { |
985 |
if (action == null) |
986 |
throw new NullPointerException(); |
987 |
if (getFence() > index && index >= 0) { |
988 |
@SuppressWarnings("unchecked") E e = (E) array[index++]; |
989 |
action.accept(e); |
990 |
return true; |
991 |
} |
992 |
return false; |
993 |
} |
994 |
|
995 |
public long estimateSize() { return (long)(getFence() - index); } |
996 |
|
997 |
public int characteristics() { |
998 |
return Spliterator.NONNULL | Spliterator.SIZED | Spliterator.SUBSIZED; |
999 |
} |
1000 |
} |
1001 |
|
1002 |
public Spliterator<E> spliterator() { |
1003 |
return new PBQSpliterator<E>(this, null, 0, -1); |
1004 |
} |
1005 |
|
1006 |
// Unsafe mechanics |
1007 |
private static final sun.misc.Unsafe UNSAFE; |
1008 |
private static final long allocationSpinLockOffset; |
1009 |
static { |
1010 |
try { |
1011 |
UNSAFE = sun.misc.Unsafe.getUnsafe(); |
1012 |
Class<?> k = PriorityBlockingQueue.class; |
1013 |
allocationSpinLockOffset = UNSAFE.objectFieldOffset |
1014 |
(k.getDeclaredField("allocationSpinLock")); |
1015 |
} catch (Exception e) { |
1016 |
throw new Error(e); |
1017 |
} |
1018 |
} |
1019 |
} |