1 /* 2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 3 * 4 * This code is free software; you can redistribute it and/or modify it 5 * under the terms of the GNU General Public License version 2 only, as 6 * published by the Free Software Foundation. Oracle designates this 7 * particular file as subject to the "Classpath" exception as provided 8 * by Oracle in the LICENSE file that accompanied this code. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 */ 24 25 /* 26 * This file is available under and governed by the GNU General Public 27 * License version 2 only, as published by the Free Software Foundation. 28 * However, the following notice accompanied the original version of this 29 * file: 30 * 31 * Written by Doug Lea with assistance from members of JCP JSR-166 32 * Expert Group and released to the public domain, as explained at 33 * http://creativecommons.org/publicdomain/zero/1.0/ 34 */ 35 36 package java.util.concurrent; 37 38 import java.lang.invoke.MethodHandles; 39 import java.lang.invoke.VarHandle; 40 import java.util.AbstractQueue; 41 import java.util.Arrays; 42 import java.util.Collection; 43 import java.util.Comparator; 44 import java.util.Iterator; 45 import java.util.NoSuchElementException; 46 import java.util.Objects; 47 import java.util.PriorityQueue; 48 import java.util.Queue; 49 import java.util.SortedSet; 50 import java.util.Spliterator; 51 import java.util.concurrent.locks.Condition; 52 import java.util.concurrent.locks.ReentrantLock; 53 import java.util.function.Consumer; 54 import java.util.function.Predicate; 55 import jdk.internal.access.SharedSecrets; 56 57 /** 58 * An unbounded {@linkplain BlockingQueue blocking queue} that uses 59 * the same ordering rules as class {@link PriorityQueue} and supplies 60 * blocking retrieval operations. While this queue is logically 61 * unbounded, attempted additions may fail due to resource exhaustion 62 * (causing {@code OutOfMemoryError}). This class does not permit 63 * {@code null} elements. A priority queue relying on {@linkplain 64 * Comparable natural ordering} also does not permit insertion of 65 * non-comparable objects (doing so results in 66 * {@code ClassCastException}). 67 * 68 * <p>This class and its iterator implement all of the <em>optional</em> 69 * methods of the {@link Collection} and {@link Iterator} interfaces. 70 * The Iterator provided in method {@link #iterator()} and the 71 * Spliterator provided in method {@link #spliterator()} are <em>not</em> 72 * guaranteed to traverse the elements of the PriorityBlockingQueue in 73 * any particular order. If you need ordered traversal, consider using 74 * {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo} can 75 * be used to <em>remove</em> some or all elements in priority order and 76 * place them in another collection. 77 * 78 * <p>Operations on this class make no guarantees about the ordering 79 * of elements with equal priority. If you need to enforce an 80 * ordering, you can define custom classes or comparators that use a 81 * secondary key to break ties in primary priority values. For 82 * example, here is a class that applies first-in-first-out 83 * tie-breaking to comparable elements. To use it, you would insert a 84 * {@code new FIFOEntry(anEntry)} instead of a plain entry object. 85 * 86 * <pre> {@code 87 * class FIFOEntry<E extends Comparable<? super E>> 88 * implements Comparable<FIFOEntry<E>> { 89 * static final AtomicLong seq = new AtomicLong(0); 90 * final long seqNum; 91 * final E entry; 92 * public FIFOEntry(E entry) { 93 * seqNum = seq.getAndIncrement(); 94 * this.entry = entry; 95 * } 96 * public E getEntry() { return entry; } 97 * public int compareTo(FIFOEntry<E> other) { 98 * int res = entry.compareTo(other.entry); 99 * if (res == 0 && other.entry != this.entry) 100 * res = (seqNum < other.seqNum ? -1 : 1); 101 * return res; 102 * } 103 * }}</pre> 104 * 105 * <p>This class is a member of the 106 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> 107 * Java Collections Framework</a>. 108 * 109 * @since 1.5 110 * @author Doug Lea 111 * @param <E> the type of elements held in this queue 112 */ 113 @SuppressWarnings("unchecked") 114 public class PriorityBlockingQueue<E> extends AbstractQueue<E> 115 implements BlockingQueue<E>, java.io.Serializable { 116 private static final long serialVersionUID = 5595510919245408276L; 117 118 /* 119 * The implementation uses an array-based binary heap, with public 120 * operations protected with a single lock. However, allocation 121 * during resizing uses a simple spinlock (used only while not 122 * holding main lock) in order to allow takes to operate 123 * concurrently with allocation. This avoids repeated 124 * postponement of waiting consumers and consequent element 125 * build-up. The need to back away from lock during allocation 126 * makes it impossible to simply wrap delegated 127 * java.util.PriorityQueue operations within a lock, as was done 128 * in a previous version of this class. To maintain 129 * interoperability, a plain PriorityQueue is still used during 130 * serialization, which maintains compatibility at the expense of 131 * transiently doubling overhead. 132 */ 133 134 /** 135 * Default array capacity. 136 */ 137 private static final int DEFAULT_INITIAL_CAPACITY = 11; 138 139 /** 140 * The maximum size of array to allocate. 141 * Some VMs reserve some header words in an array. 142 * Attempts to allocate larger arrays may result in 143 * OutOfMemoryError: Requested array size exceeds VM limit 144 */ 145 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; 146 147 /** 148 * Priority queue represented as a balanced binary heap: the two 149 * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The 150 * priority queue is ordered by comparator, or by the elements' 151 * natural ordering, if comparator is null: For each node n in the 152 * heap and each descendant d of n, n <= d. The element with the 153 * lowest value is in queue[0], assuming the queue is nonempty. 154 */ 155 private transient Object[] queue; 156 157 /** 158 * The number of elements in the priority queue. 159 */ 160 private transient int size; 161 162 /** 163 * The comparator, or null if priority queue uses elements' 164 * natural ordering. 165 */ 166 private transient Comparator<? super E> comparator; 167 168 /** 169 * Lock used for all public operations. 170 */ 171 private final ReentrantLock lock = new ReentrantLock(); 172 173 /** 174 * Condition for blocking when empty. 175 */ 176 private final Condition notEmpty = lock.newCondition(); 177 178 /** 179 * Spinlock for allocation, acquired via CAS. 180 */ 181 private transient volatile int allocationSpinLock; 182 183 /** 184 * A plain PriorityQueue used only for serialization, 185 * to maintain compatibility with previous versions 186 * of this class. Non-null only during serialization/deserialization. 187 */ 188 private PriorityQueue<E> q; 189 190 /** 191 * Creates a {@code PriorityBlockingQueue} with the default 192 * initial capacity (11) that orders its elements according to 193 * their {@linkplain Comparable natural ordering}. 194 */ 195 public PriorityBlockingQueue() { 196 this(DEFAULT_INITIAL_CAPACITY, null); 197 } 198 199 /** 200 * Creates a {@code PriorityBlockingQueue} with the specified 201 * initial capacity that orders its elements according to their 202 * {@linkplain Comparable natural ordering}. 203 * 204 * @param initialCapacity the initial capacity for this priority queue 205 * @throws IllegalArgumentException if {@code initialCapacity} is less 206 * than 1 207 */ 208 public PriorityBlockingQueue(int initialCapacity) { 209 this(initialCapacity, null); 210 } 211 212 /** 213 * Creates a {@code PriorityBlockingQueue} with the specified initial 214 * capacity that orders its elements according to the specified 215 * comparator. 216 * 217 * @param initialCapacity the initial capacity for this priority queue 218 * @param comparator the comparator that will be used to order this 219 * priority queue. If {@code null}, the {@linkplain Comparable 220 * natural ordering} of the elements will be used. 221 * @throws IllegalArgumentException if {@code initialCapacity} is less 222 * than 1 223 */ 224 public PriorityBlockingQueue(int initialCapacity, 225 Comparator<? super E> comparator) { 226 if (initialCapacity < 1) 227 throw new IllegalArgumentException(); 228 this.comparator = comparator; 229 this.queue = new Object[Math.max(1, initialCapacity)]; 230 } 231 232 /** 233 * Creates a {@code PriorityBlockingQueue} containing the elements 234 * in the specified collection. If the specified collection is a 235 * {@link SortedSet} or a {@link PriorityQueue}, this 236 * priority queue will be ordered according to the same ordering. 237 * Otherwise, this priority queue will be ordered according to the 238 * {@linkplain Comparable natural ordering} of its elements. 239 * 240 * @param c the collection whose elements are to be placed 241 * into this priority queue 242 * @throws ClassCastException if elements of the specified collection 243 * cannot be compared to one another according to the priority 244 * queue's ordering 245 * @throws NullPointerException if the specified collection or any 246 * of its elements are null 247 */ 248 public PriorityBlockingQueue(Collection<? extends E> c) { 249 boolean heapify = true; // true if not known to be in heap order 250 boolean screen = true; // true if must screen for nulls 251 if (c instanceof SortedSet<?>) { 252 SortedSet<? extends E> ss = (SortedSet<? extends E>) c; 253 this.comparator = (Comparator<? super E>) ss.comparator(); 254 heapify = false; 255 } 256 else if (c instanceof PriorityBlockingQueue<?>) { 257 PriorityBlockingQueue<? extends E> pq = 258 (PriorityBlockingQueue<? extends E>) c; 259 this.comparator = (Comparator<? super E>) pq.comparator(); 260 screen = false; 261 if (pq.getClass() == PriorityBlockingQueue.class) // exact match 262 heapify = false; 263 } 264 Object[] es = c.toArray(); 265 int n = es.length; 266 // If c.toArray incorrectly doesn't return Object[], copy it. 267 if (es.getClass() != Object[].class) 268 es = Arrays.copyOf(es, n, Object[].class); 269 if (screen && (n == 1 || this.comparator != null)) { 270 for (Object e : es) 271 if (e == null) 272 throw new NullPointerException(); 273 } 274 this.queue = ensureNonEmpty(es); 275 this.size = n; 276 if (heapify) 277 heapify(); 278 } 279 280 /** Ensures that queue[0] exists, helping peek() and poll(). */ 281 private static Object[] ensureNonEmpty(Object[] es) { 282 return (es.length > 0) ? es : new Object[1]; 283 } 284 285 /** 286 * Tries to grow array to accommodate at least one more element 287 * (but normally expand by about 50%), giving up (allowing retry) 288 * on contention (which we expect to be rare). Call only while 289 * holding lock. 290 * 291 * @param array the heap array 292 * @param oldCap the length of the array 293 */ 294 private void tryGrow(Object[] array, int oldCap) { 295 lock.unlock(); // must release and then re-acquire main lock 296 Object[] newArray = null; 297 if (allocationSpinLock == 0 && 298 ALLOCATIONSPINLOCK.compareAndSet(this, 0, 1)) { 299 try { 300 int newCap = oldCap + ((oldCap < 64) ? 301 (oldCap + 2) : // grow faster if small 302 (oldCap >> 1)); 303 if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow 304 int minCap = oldCap + 1; 305 if (minCap < 0 || minCap > MAX_ARRAY_SIZE) 306 throw new OutOfMemoryError(); 307 newCap = MAX_ARRAY_SIZE; 308 } 309 if (newCap > oldCap && queue == array) 310 newArray = new Object[newCap]; 311 } finally { 312 allocationSpinLock = 0; 313 } 314 } 315 if (newArray == null) // back off if another thread is allocating 316 Thread.yield(); 317 lock.lock(); 318 if (newArray != null && queue == array) { 319 queue = newArray; 320 System.arraycopy(array, 0, newArray, 0, oldCap); 321 } 322 } 323 324 /** 325 * Mechanics for poll(). Call only while holding lock. 326 */ 327 private E dequeue() { 328 // assert lock.isHeldByCurrentThread(); 329 final Object[] es; 330 final E result; 331 332 if ((result = (E) ((es = queue)[0])) != null) { 333 final int n; 334 final E x = (E) es[(n = --size)]; 335 es[n] = null; 336 if (n > 0) { 337 final Comparator<? super E> cmp; 338 if ((cmp = comparator) == null) 339 siftDownComparable(0, x, es, n); 340 else 341 siftDownUsingComparator(0, x, es, n, cmp); 342 } 343 } 344 return result; 345 } 346 347 /** 348 * Inserts item x at position k, maintaining heap invariant by 349 * promoting x up the tree until it is greater than or equal to 350 * its parent, or is the root. 351 * 352 * To simplify and speed up coercions and comparisons, the 353 * Comparable and Comparator versions are separated into different 354 * methods that are otherwise identical. (Similarly for siftDown.) 355 * 356 * @param k the position to fill 357 * @param x the item to insert 358 * @param es the heap array 359 */ 360 private static <T> void siftUpComparable(int k, T x, Object[] es) { 361 Comparable<? super T> key = (Comparable<? super T>) x; 362 while (k > 0) { 363 int parent = (k - 1) >>> 1; 364 Object e = es[parent]; 365 if (key.compareTo((T) e) >= 0) 366 break; 367 es[k] = e; 368 k = parent; 369 } 370 es[k] = key; 371 } 372 373 private static <T> void siftUpUsingComparator( 374 int k, T x, Object[] es, Comparator<? super T> cmp) { 375 while (k > 0) { 376 int parent = (k - 1) >>> 1; 377 Object e = es[parent]; 378 if (cmp.compare(x, (T) e) >= 0) 379 break; 380 es[k] = e; 381 k = parent; 382 } 383 es[k] = x; 384 } 385 386 /** 387 * Inserts item x at position k, maintaining heap invariant by 388 * demoting x down the tree repeatedly until it is less than or 389 * equal to its children or is a leaf. 390 * 391 * @param k the position to fill 392 * @param x the item to insert 393 * @param es the heap array 394 * @param n heap size 395 */ 396 private static <T> void siftDownComparable(int k, T x, Object[] es, int n) { 397 // assert n > 0; 398 Comparable<? super T> key = (Comparable<? super T>)x; 399 int half = n >>> 1; // loop while a non-leaf 400 while (k < half) { 401 int child = (k << 1) + 1; // assume left child is least 402 Object c = es[child]; 403 int right = child + 1; 404 if (right < n && 405 ((Comparable<? super T>) c).compareTo((T) es[right]) > 0) 406 c = es[child = right]; 407 if (key.compareTo((T) c) <= 0) 408 break; 409 es[k] = c; 410 k = child; 411 } 412 es[k] = key; 413 } 414 415 private static <T> void siftDownUsingComparator( 416 int k, T x, Object[] es, int n, Comparator<? super T> cmp) { 417 // assert n > 0; 418 int half = n >>> 1; 419 while (k < half) { 420 int child = (k << 1) + 1; 421 Object c = es[child]; 422 int right = child + 1; 423 if (right < n && cmp.compare((T) c, (T) es[right]) > 0) 424 c = es[child = right]; 425 if (cmp.compare(x, (T) c) <= 0) 426 break; 427 es[k] = c; 428 k = child; 429 } 430 es[k] = x; 431 } 432 433 /** 434 * Establishes the heap invariant (described above) in the entire tree, 435 * assuming nothing about the order of the elements prior to the call. 436 * This classic algorithm due to Floyd (1964) is known to be O(size). 437 */ 438 private void heapify() { 439 final Object[] es = queue; 440 int n = size, i = (n >>> 1) - 1; 441 final Comparator<? super E> cmp; 442 if ((cmp = comparator) == null) 443 for (; i >= 0; i--) 444 siftDownComparable(i, (E) es[i], es, n); 445 else 446 for (; i >= 0; i--) 447 siftDownUsingComparator(i, (E) es[i], es, n, cmp); 448 } 449 450 /** 451 * Inserts the specified element into this priority queue. 452 * 453 * @param e the element to add 454 * @return {@code true} (as specified by {@link Collection#add}) 455 * @throws ClassCastException if the specified element cannot be compared 456 * with elements currently in the priority queue according to the 457 * priority queue's ordering 458 * @throws NullPointerException if the specified element is null 459 */ 460 public boolean add(E e) { 461 return offer(e); 462 } 463 464 /** 465 * Inserts the specified element into this priority queue. 466 * As the queue is unbounded, this method will never return {@code false}. 467 * 468 * @param e the element to add 469 * @return {@code true} (as specified by {@link Queue#offer}) 470 * @throws ClassCastException if the specified element cannot be compared 471 * with elements currently in the priority queue according to the 472 * priority queue's ordering 473 * @throws NullPointerException if the specified element is null 474 */ 475 public boolean offer(E e) { 476 if (e == null) 477 throw new NullPointerException(); 478 final ReentrantLock lock = this.lock; 479 lock.lock(); 480 int n, cap; 481 Object[] es; 482 while ((n = size) >= (cap = (es = queue).length)) 483 tryGrow(es, cap); 484 try { 485 final Comparator<? super E> cmp; 486 if ((cmp = comparator) == null) 487 siftUpComparable(n, e, es); 488 else 489 siftUpUsingComparator(n, e, es, cmp); 490 size = n + 1; 491 notEmpty.signal(); 492 } finally { 493 lock.unlock(); 494 } 495 return true; 496 } 497 498 /** 499 * Inserts the specified element into this priority queue. 500 * As the queue is unbounded, this method will never block. 501 * 502 * @param e the element to add 503 * @throws ClassCastException if the specified element cannot be compared 504 * with elements currently in the priority queue according to the 505 * priority queue's ordering 506 * @throws NullPointerException if the specified element is null 507 */ 508 public void put(E e) { 509 offer(e); // never need to block 510 } 511 512 /** 513 * Inserts the specified element into this priority queue. 514 * As the queue is unbounded, this method will never block or 515 * return {@code false}. 516 * 517 * @param e the element to add 518 * @param timeout This parameter is ignored as the method never blocks 519 * @param unit This parameter is ignored as the method never blocks 520 * @return {@code true} (as specified by 521 * {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) 522 * @throws ClassCastException if the specified element cannot be compared 523 * with elements currently in the priority queue according to the 524 * priority queue's ordering 525 * @throws NullPointerException if the specified element is null 526 */ 527 public boolean offer(E e, long timeout, TimeUnit unit) { 528 return offer(e); // never need to block 529 } 530 531 public E poll() { 532 final ReentrantLock lock = this.lock; 533 lock.lock(); 534 try { 535 return dequeue(); 536 } finally { 537 lock.unlock(); 538 } 539 } 540 541 public E take() throws InterruptedException { 542 final ReentrantLock lock = this.lock; 543 lock.lockInterruptibly(); 544 E result; 545 try { 546 while ( (result = dequeue()) == null) 547 notEmpty.await(); 548 } finally { 549 lock.unlock(); 550 } 551 return result; 552 } 553 554 public E poll(long timeout, TimeUnit unit) throws InterruptedException { 555 long nanos = unit.toNanos(timeout); 556 final ReentrantLock lock = this.lock; 557 lock.lockInterruptibly(); 558 E result; 559 try { 560 while ( (result = dequeue()) == null && nanos > 0) 561 nanos = notEmpty.awaitNanos(nanos); 562 } finally { 563 lock.unlock(); 564 } 565 return result; 566 } 567 568 public E peek() { 569 final ReentrantLock lock = this.lock; 570 lock.lock(); 571 try { 572 return (E) queue[0]; 573 } finally { 574 lock.unlock(); 575 } 576 } 577 578 /** 579 * Returns the comparator used to order the elements in this queue, 580 * or {@code null} if this queue uses the {@linkplain Comparable 581 * natural ordering} of its elements. 582 * 583 * @return the comparator used to order the elements in this queue, 584 * or {@code null} if this queue uses the natural 585 * ordering of its elements 586 */ 587 public Comparator<? super E> comparator() { 588 return comparator; 589 } 590 591 public int size() { 592 final ReentrantLock lock = this.lock; 593 lock.lock(); 594 try { 595 return size; 596 } finally { 597 lock.unlock(); 598 } 599 } 600 601 /** 602 * Always returns {@code Integer.MAX_VALUE} because 603 * a {@code PriorityBlockingQueue} is not capacity constrained. 604 * @return {@code Integer.MAX_VALUE} always 605 */ 606 public int remainingCapacity() { 607 return Integer.MAX_VALUE; 608 } 609 610 private int indexOf(Object o) { 611 if (o != null) { 612 final Object[] es = queue; 613 for (int i = 0, n = size; i < n; i++) 614 if (o.equals(es[i])) 615 return i; 616 } 617 return -1; 618 } 619 620 /** 621 * Removes the ith element from queue. 622 */ 623 private void removeAt(int i) { 624 final Object[] es = queue; 625 final int n = size - 1; 626 if (n == i) // removed last element 627 es[i] = null; 628 else { 629 E moved = (E) es[n]; 630 es[n] = null; 631 final Comparator<? super E> cmp; 632 if ((cmp = comparator) == null) 633 siftDownComparable(i, moved, es, n); 634 else 635 siftDownUsingComparator(i, moved, es, n, cmp); 636 if (es[i] == moved) { 637 if (cmp == null) 638 siftUpComparable(i, moved, es); 639 else 640 siftUpUsingComparator(i, moved, es, cmp); 641 } 642 } 643 size = n; 644 } 645 646 /** 647 * Removes a single instance of the specified element from this queue, 648 * if it is present. More formally, removes an element {@code e} such 649 * that {@code o.equals(e)}, if this queue contains one or more such 650 * elements. Returns {@code true} if and only if this queue contained 651 * the specified element (or equivalently, if this queue changed as a 652 * result of the call). 653 * 654 * @param o element to be removed from this queue, if present 655 * @return {@code true} if this queue changed as a result of the call 656 */ 657 public boolean remove(Object o) { 658 final ReentrantLock lock = this.lock; 659 lock.lock(); 660 try { 661 int i = indexOf(o); 662 if (i == -1) 663 return false; 664 removeAt(i); 665 return true; 666 } finally { 667 lock.unlock(); 668 } 669 } 670 671 /** 672 * Identity-based version for use in Itr.remove. 673 * 674 * @param o element to be removed from this queue, if present 675 */ 676 void removeEq(Object o) { 677 final ReentrantLock lock = this.lock; 678 lock.lock(); 679 try { 680 final Object[] es = queue; 681 for (int i = 0, n = size; i < n; i++) { 682 if (o == es[i]) { 683 removeAt(i); 684 break; 685 } 686 } 687 } finally { 688 lock.unlock(); 689 } 690 } 691 692 /** 693 * Returns {@code true} if this queue contains the specified element. 694 * More formally, returns {@code true} if and only if this queue contains 695 * at least one element {@code e} such that {@code o.equals(e)}. 696 * 697 * @param o object to be checked for containment in this queue 698 * @return {@code true} if this queue contains the specified element 699 */ 700 public boolean contains(Object o) { 701 final ReentrantLock lock = this.lock; 702 lock.lock(); 703 try { 704 return indexOf(o) != -1; 705 } finally { 706 lock.unlock(); 707 } 708 } 709 710 public String toString() { 711 return Helpers.collectionToString(this); 712 } 713 714 /** 715 * @throws UnsupportedOperationException {@inheritDoc} 716 * @throws ClassCastException {@inheritDoc} 717 * @throws NullPointerException {@inheritDoc} 718 * @throws IllegalArgumentException {@inheritDoc} 719 */ 720 public int drainTo(Collection<? super E> c) { 721 return drainTo(c, Integer.MAX_VALUE); 722 } 723 724 /** 725 * @throws UnsupportedOperationException {@inheritDoc} 726 * @throws ClassCastException {@inheritDoc} 727 * @throws NullPointerException {@inheritDoc} 728 * @throws IllegalArgumentException {@inheritDoc} 729 */ 730 public int drainTo(Collection<? super E> c, int maxElements) { 731 Objects.requireNonNull(c); 732 if (c == this) 733 throw new IllegalArgumentException(); 734 if (maxElements <= 0) 735 return 0; 736 final ReentrantLock lock = this.lock; 737 lock.lock(); 738 try { 739 int n = Math.min(size, maxElements); 740 for (int i = 0; i < n; i++) { 741 c.add((E) queue[0]); // In this order, in case add() throws. 742 dequeue(); 743 } 744 return n; 745 } finally { 746 lock.unlock(); 747 } 748 } 749 750 /** 751 * Atomically removes all of the elements from this queue. 752 * The queue will be empty after this call returns. 753 */ 754 public void clear() { 755 final ReentrantLock lock = this.lock; 756 lock.lock(); 757 try { 758 final Object[] es = queue; 759 for (int i = 0, n = size; i < n; i++) 760 es[i] = null; 761 size = 0; 762 } finally { 763 lock.unlock(); 764 } 765 } 766 767 /** 768 * Returns an array containing all of the elements in this queue. 769 * The returned array elements are in no particular order. 770 * 771 * <p>The returned array will be "safe" in that no references to it are 772 * maintained by this queue. (In other words, this method must allocate 773 * a new array). The caller is thus free to modify the returned array. 774 * 775 * <p>This method acts as bridge between array-based and collection-based 776 * APIs. 777 * 778 * @return an array containing all of the elements in this queue 779 */ 780 public Object[] toArray() { 781 final ReentrantLock lock = this.lock; 782 lock.lock(); 783 try { 784 return Arrays.copyOf(queue, size); 785 } finally { 786 lock.unlock(); 787 } 788 } 789 790 /** 791 * Returns an array containing all of the elements in this queue; the 792 * runtime type of the returned array is that of the specified array. 793 * The returned array elements are in no particular order. 794 * If the queue fits in the specified array, it is returned therein. 795 * Otherwise, a new array is allocated with the runtime type of the 796 * specified array and the size of this queue. 797 * 798 * <p>If this queue fits in the specified array with room to spare 799 * (i.e., the array has more elements than this queue), the element in 800 * the array immediately following the end of the queue is set to 801 * {@code null}. 802 * 803 * <p>Like the {@link #toArray()} method, this method acts as bridge between 804 * array-based and collection-based APIs. Further, this method allows 805 * precise control over the runtime type of the output array, and may, 806 * under certain circumstances, be used to save allocation costs. 807 * 808 * <p>Suppose {@code x} is a queue known to contain only strings. 809 * The following code can be used to dump the queue into a newly 810 * allocated array of {@code String}: 811 * 812 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre> 813 * 814 * Note that {@code toArray(new Object[0])} is identical in function to 815 * {@code toArray()}. 816 * 817 * @param a the array into which the elements of the queue are to 818 * be stored, if it is big enough; otherwise, a new array of the 819 * same runtime type is allocated for this purpose 820 * @return an array containing all of the elements in this queue 821 * @throws ArrayStoreException if the runtime type of the specified array 822 * is not a supertype of the runtime type of every element in 823 * this queue 824 * @throws NullPointerException if the specified array is null 825 */ 826 public <T> T[] toArray(T[] a) { 827 final ReentrantLock lock = this.lock; 828 lock.lock(); 829 try { 830 int n = size; 831 if (a.length < n) 832 // Make a new array of a's runtime type, but my contents: 833 return (T[]) Arrays.copyOf(queue, size, a.getClass()); 834 System.arraycopy(queue, 0, a, 0, n); 835 if (a.length > n) 836 a[n] = null; 837 return a; 838 } finally { 839 lock.unlock(); 840 } 841 } 842 843 /** 844 * Returns an iterator over the elements in this queue. The 845 * iterator does not return the elements in any particular order. 846 * 847 * <p>The returned iterator is 848 * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. 849 * 850 * @return an iterator over the elements in this queue 851 */ 852 public Iterator<E> iterator() { 853 return new Itr(toArray()); 854 } 855 856 /** 857 * Snapshot iterator that works off copy of underlying q array. 858 */ 859 final class Itr implements Iterator<E> { 860 final Object[] array; // Array of all elements 861 int cursor; // index of next element to return 862 int lastRet = -1; // index of last element, or -1 if no such 863 864 Itr(Object[] array) { 865 this.array = array; 866 } 867 868 public boolean hasNext() { 869 return cursor < array.length; 870 } 871 872 public E next() { 873 if (cursor >= array.length) 874 throw new NoSuchElementException(); 875 return (E)array[lastRet = cursor++]; 876 } 877 878 public void remove() { 879 if (lastRet < 0) 880 throw new IllegalStateException(); 881 removeEq(array[lastRet]); 882 lastRet = -1; 883 } 884 885 public void forEachRemaining(Consumer<? super E> action) { 886 Objects.requireNonNull(action); 887 final Object[] es = array; 888 int i; 889 if ((i = cursor) < es.length) { 890 lastRet = -1; 891 cursor = es.length; 892 for (; i < es.length; i++) 893 action.accept((E) es[i]); 894 lastRet = es.length - 1; 895 } 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 int sz = q.size(); 935 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, sz); 936 this.queue = new Object[Math.max(1, sz)]; 937 comparator = q.comparator(); 938 addAll(q); 939 } finally { 940 q = null; 941 } 942 } 943 944 /** 945 * Immutable snapshot spliterator that binds to elements "late". 946 */ 947 final class PBQSpliterator implements Spliterator<E> { 948 Object[] array; // null until late-bound-initialized 949 int index; 950 int fence; 951 952 PBQSpliterator() {} 953 954 PBQSpliterator(Object[] array, int index, int fence) { 955 this.array = array; 956 this.index = index; 957 this.fence = fence; 958 } 959 960 private int getFence() { 961 if (array == null) 962 fence = (array = toArray()).length; 963 return fence; 964 } 965 966 public PBQSpliterator trySplit() { 967 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 968 return (lo >= mid) ? null : 969 new PBQSpliterator(array, lo, index = mid); 970 } 971 972 public void forEachRemaining(Consumer<? super E> action) { 973 Objects.requireNonNull(action); 974 final int hi = getFence(), lo = index; 975 final Object[] es = array; 976 index = hi; // ensure exhaustion 977 for (int i = lo; i < hi; i++) 978 action.accept((E) es[i]); 979 } 980 981 public boolean tryAdvance(Consumer<? super E> action) { 982 Objects.requireNonNull(action); 983 if (getFence() > index && index >= 0) { 984 action.accept((E) array[index++]); 985 return true; 986 } 987 return false; 988 } 989 990 public long estimateSize() { return getFence() - index; } 991 992 public int characteristics() { 993 return (Spliterator.NONNULL | 994 Spliterator.SIZED | 995 Spliterator.SUBSIZED); 996 } 997 } 998 999 /** 1000 * Returns a {@link Spliterator} over the elements in this queue. 1001 * The spliterator does not traverse elements in any particular order 1002 * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported). 1003 * 1004 * <p>The returned spliterator is 1005 * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. 1006 * 1007 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and 1008 * {@link Spliterator#NONNULL}. 1009 * 1010 * @implNote 1011 * The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}. 1012 * 1013 * @return a {@code Spliterator} over the elements in this queue 1014 * @since 1.8 1015 */ 1016 public Spliterator<E> spliterator() { 1017 return new PBQSpliterator(); 1018 } 1019 1020 /** 1021 * @throws NullPointerException {@inheritDoc} 1022 */ 1023 public boolean removeIf(Predicate<? super E> filter) { 1024 Objects.requireNonNull(filter); 1025 return bulkRemove(filter); 1026 } 1027 1028 /** 1029 * @throws NullPointerException {@inheritDoc} 1030 */ 1031 public boolean removeAll(Collection<?> c) { 1032 Objects.requireNonNull(c); 1033 return bulkRemove(e -> c.contains(e)); 1034 } 1035 1036 /** 1037 * @throws NullPointerException {@inheritDoc} 1038 */ 1039 public boolean retainAll(Collection<?> c) { 1040 Objects.requireNonNull(c); 1041 return bulkRemove(e -> !c.contains(e)); 1042 } 1043 1044 // A tiny bit set implementation 1045 1046 private static long[] nBits(int n) { 1047 return new long[((n - 1) >> 6) + 1]; 1048 } 1049 private static void setBit(long[] bits, int i) { 1050 bits[i >> 6] |= 1L << i; 1051 } 1052 private static boolean isClear(long[] bits, int i) { 1053 return (bits[i >> 6] & (1L << i)) == 0; 1054 } 1055 1056 /** Implementation of bulk remove methods. */ 1057 private boolean bulkRemove(Predicate<? super E> filter) { 1058 final ReentrantLock lock = this.lock; 1059 lock.lock(); 1060 try { 1061 final Object[] es = queue; 1062 final int end = size; 1063 int i; 1064 // Optimize for initial run of survivors 1065 for (i = 0; i < end && !filter.test((E) es[i]); i++) 1066 ; 1067 if (i >= end) 1068 return false; 1069 // Tolerate predicates that reentrantly access the 1070 // collection for read, so traverse once to find elements 1071 // to delete, a second pass to physically expunge. 1072 final int beg = i; 1073 final long[] deathRow = nBits(end - beg); 1074 deathRow[0] = 1L; // set bit 0 1075 for (i = beg + 1; i < end; i++) 1076 if (filter.test((E) es[i])) 1077 setBit(deathRow, i - beg); 1078 int w = beg; 1079 for (i = beg; i < end; i++) 1080 if (isClear(deathRow, i - beg)) 1081 es[w++] = es[i]; 1082 for (i = size = w; i < end; i++) 1083 es[i] = null; 1084 heapify(); 1085 return true; 1086 } finally { 1087 lock.unlock(); 1088 } 1089 } 1090 1091 /** 1092 * @throws NullPointerException {@inheritDoc} 1093 */ 1094 public void forEach(Consumer<? super E> action) { 1095 Objects.requireNonNull(action); 1096 final ReentrantLock lock = this.lock; 1097 lock.lock(); 1098 try { 1099 final Object[] es = queue; 1100 for (int i = 0, n = size; i < n; i++) 1101 action.accept((E) es[i]); 1102 } finally { 1103 lock.unlock(); 1104 } 1105 } 1106 1107 // VarHandle mechanics 1108 private static final VarHandle ALLOCATIONSPINLOCK; 1109 static { 1110 try { 1111 MethodHandles.Lookup l = MethodHandles.lookup(); 1112 ALLOCATIONSPINLOCK = l.findVarHandle(PriorityBlockingQueue.class, 1113 "allocationSpinLock", 1114 int.class); 1115 } catch (ReflectiveOperationException e) { 1116 throw new ExceptionInInitializerError(e); 1117 } 1118 } 1119 }