1 /* 2 * Copyright (c) 2003, 2011, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 /* 27 * Written by Doug Lea with assistance from members of JCP JSR-166 28 * Expert Group. Adapted and released, under explicit permission, 29 * from JDK ArrayList.java which carries the following copyright: 30 * 31 * Copyright 1997 by Sun Microsystems, Inc., 32 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A. 33 * All rights reserved. 34 */ 35 36 package java.util.concurrent; 37 import java.util.*; 38 import java.util.concurrent.locks.*; 39 import sun.misc.Unsafe; 40 41 /** 42 * A thread-safe variant of {@link java.util.ArrayList} in which all mutative 43 * operations (<tt>add</tt>, <tt>set</tt>, and so on) are implemented by 44 * making a fresh copy of the underlying array. 45 * 46 * <p> This is ordinarily too costly, but may be <em>more</em> efficient 47 * than alternatives when traversal operations vastly outnumber 48 * mutations, and is useful when you cannot or don't want to 49 * synchronize traversals, yet need to preclude interference among 50 * concurrent threads. The "snapshot" style iterator method uses a 51 * reference to the state of the array at the point that the iterator 52 * was created. This array never changes during the lifetime of the 53 * iterator, so interference is impossible and the iterator is 54 * guaranteed not to throw <tt>ConcurrentModificationException</tt>. 55 * The iterator will not reflect additions, removals, or changes to 56 * the list since the iterator was created. Element-changing 57 * operations on iterators themselves (<tt>remove</tt>, <tt>set</tt>, and 58 * <tt>add</tt>) are not supported. These methods throw 59 * <tt>UnsupportedOperationException</tt>. 60 * 61 * <p>All elements are permitted, including <tt>null</tt>. 62 * 63 * <p>Memory consistency effects: As with other concurrent 64 * collections, actions in a thread prior to placing an object into a 65 * {@code CopyOnWriteArrayList} 66 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> 67 * actions subsequent to the access or removal of that element from 68 * the {@code CopyOnWriteArrayList} in another thread. 69 * 70 * <p>This class is a member of the 71 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 72 * Java Collections Framework</a>. 73 * 74 * @since 1.5 75 * @author Doug Lea 76 * @param <E> the type of elements held in this collection 77 */ 78 public class CopyOnWriteArrayList<E> 79 implements List<E>, RandomAccess, Cloneable, java.io.Serializable { 80 private static final long serialVersionUID = 8673264195747942595L; 81 82 /** The lock protecting all mutators */ 83 transient final ReentrantLock lock = new ReentrantLock(); 84 85 /** The array, accessed only via getArray/setArray. */ 86 private volatile transient Object[] array; 87 88 /** 89 * Gets the array. Non-private so as to also be accessible 90 * from CopyOnWriteArraySet class. 91 */ 92 final Object[] getArray() { 93 return array; 94 } 95 96 /** 97 * Sets the array. 98 */ 99 final void setArray(Object[] a) { 100 array = a; 101 } 102 103 /** 104 * Creates an empty list. 105 */ 106 public CopyOnWriteArrayList() { 107 setArray(new Object[0]); 108 } 109 110 /** 111 * Creates a list containing the elements of the specified 112 * collection, in the order they are returned by the collection's 113 * iterator. 114 * 115 * @param c the collection of initially held elements 116 * @throws NullPointerException if the specified collection is null 117 */ 118 public CopyOnWriteArrayList(Collection<? extends E> c) { 119 Object[] elements = c.toArray(); 120 // c.toArray might (incorrectly) not return Object[] (see 6260652) 121 if (elements.getClass() != Object[].class) 122 elements = Arrays.copyOf(elements, elements.length, Object[].class); 123 setArray(elements); 124 } 125 126 /** 127 * Creates a list holding a copy of the given array. 128 * 129 * @param toCopyIn the array (a copy of this array is used as the 130 * internal array) 131 * @throws NullPointerException if the specified array is null 132 */ 133 public CopyOnWriteArrayList(E[] toCopyIn) { 134 setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class)); 135 } 136 137 /** 138 * Returns the number of elements in this list. 139 * 140 * @return the number of elements in this list 141 */ 142 public int size() { 143 return getArray().length; 144 } 145 146 /** 147 * Returns <tt>true</tt> if this list contains no elements. 148 * 149 * @return <tt>true</tt> if this list contains no elements 150 */ 151 public boolean isEmpty() { 152 return size() == 0; 153 } 154 155 /** 156 * Test for equality, coping with nulls. 157 */ 158 private static boolean eq(Object o1, Object o2) { 159 return (o1 == null ? o2 == null : o1.equals(o2)); 160 } 161 162 /** 163 * static version of indexOf, to allow repeated calls without 164 * needing to re-acquire array each time. 165 * @param o element to search for 166 * @param elements the array 167 * @param index first index to search 168 * @param fence one past last index to search 169 * @return index of element, or -1 if absent 170 */ 171 private static int indexOf(Object o, Object[] elements, 172 int index, int fence) { 173 if (o == null) { 174 for (int i = index; i < fence; i++) 175 if (elements[i] == null) 176 return i; 177 } else { 178 for (int i = index; i < fence; i++) 179 if (o.equals(elements[i])) 180 return i; 181 } 182 return -1; 183 } 184 185 /** 186 * static version of lastIndexOf. 187 * @param o element to search for 188 * @param elements the array 189 * @param index first index to search 190 * @return index of element, or -1 if absent 191 */ 192 private static int lastIndexOf(Object o, Object[] elements, int index) { 193 if (o == null) { 194 for (int i = index; i >= 0; i--) 195 if (elements[i] == null) 196 return i; 197 } else { 198 for (int i = index; i >= 0; i--) 199 if (o.equals(elements[i])) 200 return i; 201 } 202 return -1; 203 } 204 205 /** 206 * Returns <tt>true</tt> if this list contains the specified element. 207 * More formally, returns <tt>true</tt> if and only if this list contains 208 * at least one element <tt>e</tt> such that 209 * <tt>(o==null ? e==null : o.equals(e))</tt>. 210 * 211 * @param o element whose presence in this list is to be tested 212 * @return <tt>true</tt> if this list contains the specified element 213 */ 214 public boolean contains(Object o) { 215 Object[] elements = getArray(); 216 return indexOf(o, elements, 0, elements.length) >= 0; 217 } 218 219 /** 220 * {@inheritDoc} 221 */ 222 public int indexOf(Object o) { 223 Object[] elements = getArray(); 224 return indexOf(o, elements, 0, elements.length); 225 } 226 227 /** 228 * Returns the index of the first occurrence of the specified element in 229 * this list, searching forwards from <tt>index</tt>, or returns -1 if 230 * the element is not found. 231 * More formally, returns the lowest index <tt>i</tt> such that 232 * <tt>(i >= index && (e==null ? get(i)==null : e.equals(get(i))))</tt>, 233 * or -1 if there is no such index. 234 * 235 * @param e element to search for 236 * @param index index to start searching from 237 * @return the index of the first occurrence of the element in 238 * this list at position <tt>index</tt> or later in the list; 239 * <tt>-1</tt> if the element is not found. 240 * @throws IndexOutOfBoundsException if the specified index is negative 241 */ 242 public int indexOf(E e, int index) { 243 Object[] elements = getArray(); 244 return indexOf(e, elements, index, elements.length); 245 } 246 247 /** 248 * {@inheritDoc} 249 */ 250 public int lastIndexOf(Object o) { 251 Object[] elements = getArray(); 252 return lastIndexOf(o, elements, elements.length - 1); 253 } 254 255 /** 256 * Returns the index of the last occurrence of the specified element in 257 * this list, searching backwards from <tt>index</tt>, or returns -1 if 258 * the element is not found. 259 * More formally, returns the highest index <tt>i</tt> such that 260 * <tt>(i <= index && (e==null ? get(i)==null : e.equals(get(i))))</tt>, 261 * or -1 if there is no such index. 262 * 263 * @param e element to search for 264 * @param index index to start searching backwards from 265 * @return the index of the last occurrence of the element at position 266 * less than or equal to <tt>index</tt> in this list; 267 * -1 if the element is not found. 268 * @throws IndexOutOfBoundsException if the specified index is greater 269 * than or equal to the current size of this list 270 */ 271 public int lastIndexOf(E e, int index) { 272 Object[] elements = getArray(); 273 return lastIndexOf(e, elements, index); 274 } 275 276 /** 277 * Returns a shallow copy of this list. (The elements themselves 278 * are not copied.) 279 * 280 * @return a clone of this list 281 */ 282 public Object clone() { 283 try { 284 CopyOnWriteArrayList c = (CopyOnWriteArrayList)(super.clone()); 285 c.resetLock(); 286 return c; 287 } catch (CloneNotSupportedException e) { 288 // this shouldn't happen, since we are Cloneable 289 throw new InternalError(); 290 } 291 } 292 293 /** 294 * Returns an array containing all of the elements in this list 295 * in proper sequence (from first to last element). 296 * 297 * <p>The returned array will be "safe" in that no references to it are 298 * maintained by this list. (In other words, this method must allocate 299 * a new array). The caller is thus free to modify the returned array. 300 * 301 * <p>This method acts as bridge between array-based and collection-based 302 * APIs. 303 * 304 * @return an array containing all the elements in this list 305 */ 306 public Object[] toArray() { 307 Object[] elements = getArray(); 308 return Arrays.copyOf(elements, elements.length); 309 } 310 311 /** 312 * Returns an array containing all of the elements in this list in 313 * proper sequence (from first to last element); the runtime type of 314 * the returned array is that of the specified array. If the list fits 315 * in the specified array, it is returned therein. Otherwise, a new 316 * array is allocated with the runtime type of the specified array and 317 * the size of this list. 318 * 319 * <p>If this list fits in the specified array with room to spare 320 * (i.e., the array has more elements than this list), the element in 321 * the array immediately following the end of the list is set to 322 * <tt>null</tt>. (This is useful in determining the length of this 323 * list <i>only</i> if the caller knows that this list does not contain 324 * any null elements.) 325 * 326 * <p>Like the {@link #toArray()} method, this method acts as bridge between 327 * array-based and collection-based APIs. Further, this method allows 328 * precise control over the runtime type of the output array, and may, 329 * under certain circumstances, be used to save allocation costs. 330 * 331 * <p>Suppose <tt>x</tt> is a list known to contain only strings. 332 * The following code can be used to dump the list into a newly 333 * allocated array of <tt>String</tt>: 334 * 335 * <pre> 336 * String[] y = x.toArray(new String[0]);</pre> 337 * 338 * Note that <tt>toArray(new Object[0])</tt> is identical in function to 339 * <tt>toArray()</tt>. 340 * 341 * @param a the array into which the elements of the list are to 342 * be stored, if it is big enough; otherwise, a new array of the 343 * same runtime type is allocated for this purpose. 344 * @return an array containing all the elements in this list 345 * @throws ArrayStoreException if the runtime type of the specified array 346 * is not a supertype of the runtime type of every element in 347 * this list 348 * @throws NullPointerException if the specified array is null 349 */ 350 @SuppressWarnings("unchecked") 351 public <T> T[] toArray(T a[]) { 352 Object[] elements = getArray(); 353 int len = elements.length; 354 if (a.length < len) 355 return (T[]) Arrays.copyOf(elements, len, a.getClass()); 356 else { 357 System.arraycopy(elements, 0, a, 0, len); 358 if (a.length > len) 359 a[len] = null; 360 return a; 361 } 362 } 363 364 // Positional Access Operations 365 366 @SuppressWarnings("unchecked") 367 private E get(Object[] a, int index) { 368 return (E) a[index]; 369 } 370 371 /** 372 * {@inheritDoc} 373 * 374 * @throws IndexOutOfBoundsException {@inheritDoc} 375 */ 376 public E get(int index) { 377 return get(getArray(), index); 378 } 379 380 /** 381 * Replaces the element at the specified position in this list with the 382 * specified element. 383 * 384 * @throws IndexOutOfBoundsException {@inheritDoc} 385 */ 386 public E set(int index, E element) { 387 final ReentrantLock lock = this.lock; 388 lock.lock(); 389 try { 390 Object[] elements = getArray(); 391 E oldValue = get(elements, index); 392 393 if (oldValue != element) { 394 int len = elements.length; 395 Object[] newElements = Arrays.copyOf(elements, len); 396 newElements[index] = element; 397 setArray(newElements); 398 } else { 399 // Not quite a no-op; ensures volatile write semantics 400 setArray(elements); 401 } 402 return oldValue; 403 } finally { 404 lock.unlock(); 405 } 406 } 407 408 /** 409 * Appends the specified element to the end of this list. 410 * 411 * @param e element to be appended to this list 412 * @return <tt>true</tt> (as specified by {@link Collection#add}) 413 */ 414 public boolean add(E e) { 415 final ReentrantLock lock = this.lock; 416 lock.lock(); 417 try { 418 Object[] elements = getArray(); 419 int len = elements.length; 420 Object[] newElements = Arrays.copyOf(elements, len + 1); 421 newElements[len] = e; 422 setArray(newElements); 423 return true; 424 } finally { 425 lock.unlock(); 426 } 427 } 428 429 /** 430 * Inserts the specified element at the specified position in this 431 * list. Shifts the element currently at that position (if any) and 432 * any subsequent elements to the right (adds one to their indices). 433 * 434 * @throws IndexOutOfBoundsException {@inheritDoc} 435 */ 436 public void add(int index, E element) { 437 final ReentrantLock lock = this.lock; 438 lock.lock(); 439 try { 440 Object[] elements = getArray(); 441 int len = elements.length; 442 if (index > len || index < 0) 443 throw new IndexOutOfBoundsException("Index: "+index+ 444 ", Size: "+len); 445 Object[] newElements; 446 int numMoved = len - index; 447 if (numMoved == 0) 448 newElements = Arrays.copyOf(elements, len + 1); 449 else { 450 newElements = new Object[len + 1]; 451 System.arraycopy(elements, 0, newElements, 0, index); 452 System.arraycopy(elements, index, newElements, index + 1, 453 numMoved); 454 } 455 newElements[index] = element; 456 setArray(newElements); 457 } finally { 458 lock.unlock(); 459 } 460 } 461 462 /** 463 * Removes the element at the specified position in this list. 464 * Shifts any subsequent elements to the left (subtracts one from their 465 * indices). Returns the element that was removed from the list. 466 * 467 * @throws IndexOutOfBoundsException {@inheritDoc} 468 */ 469 public E remove(int index) { 470 final ReentrantLock lock = this.lock; 471 lock.lock(); 472 try { 473 Object[] elements = getArray(); 474 int len = elements.length; 475 E oldValue = get(elements, index); 476 int numMoved = len - index - 1; 477 if (numMoved == 0) 478 setArray(Arrays.copyOf(elements, len - 1)); 479 else { 480 Object[] newElements = new Object[len - 1]; 481 System.arraycopy(elements, 0, newElements, 0, index); 482 System.arraycopy(elements, index + 1, newElements, index, 483 numMoved); 484 setArray(newElements); 485 } 486 return oldValue; 487 } finally { 488 lock.unlock(); 489 } 490 } 491 492 /** 493 * Removes the first occurrence of the specified element from this list, 494 * if it is present. If this list does not contain the element, it is 495 * unchanged. More formally, removes the element with the lowest index 496 * <tt>i</tt> such that 497 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> 498 * (if such an element exists). Returns <tt>true</tt> if this list 499 * contained the specified element (or equivalently, if this list 500 * changed as a result of the call). 501 * 502 * @param o element to be removed from this list, if present 503 * @return <tt>true</tt> if this list contained the specified element 504 */ 505 public boolean remove(Object o) { 506 final ReentrantLock lock = this.lock; 507 lock.lock(); 508 try { 509 Object[] elements = getArray(); 510 int len = elements.length; 511 if (len != 0) { 512 // Copy while searching for element to remove 513 // This wins in the normal case of element being present 514 int newlen = len - 1; 515 Object[] newElements = new Object[newlen]; 516 517 for (int i = 0; i < newlen; ++i) { 518 if (eq(o, elements[i])) { 519 // found one; copy remaining and exit 520 for (int k = i + 1; k < len; ++k) 521 newElements[k-1] = elements[k]; 522 setArray(newElements); 523 return true; 524 } else 525 newElements[i] = elements[i]; 526 } 527 528 // special handling for last cell 529 if (eq(o, elements[newlen])) { 530 setArray(newElements); 531 return true; 532 } 533 } 534 return false; 535 } finally { 536 lock.unlock(); 537 } 538 } 539 540 /** 541 * Removes from this list all of the elements whose index is between 542 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. 543 * Shifts any succeeding elements to the left (reduces their index). 544 * This call shortens the list by <tt>(toIndex - fromIndex)</tt> elements. 545 * (If <tt>toIndex==fromIndex</tt>, this operation has no effect.) 546 * 547 * @param fromIndex index of first element to be removed 548 * @param toIndex index after last element to be removed 549 * @throws IndexOutOfBoundsException if fromIndex or toIndex out of range 550 * ({@code{fromIndex < 0 || toIndex > size() || toIndex < fromIndex}) 551 */ 552 private void removeRange(int fromIndex, int toIndex) { 553 final ReentrantLock lock = this.lock; 554 lock.lock(); 555 try { 556 Object[] elements = getArray(); 557 int len = elements.length; 558 559 if (fromIndex < 0 || toIndex > len || toIndex < fromIndex) 560 throw new IndexOutOfBoundsException(); 561 int newlen = len - (toIndex - fromIndex); 562 int numMoved = len - toIndex; 563 if (numMoved == 0) 564 setArray(Arrays.copyOf(elements, newlen)); 565 else { 566 Object[] newElements = new Object[newlen]; 567 System.arraycopy(elements, 0, newElements, 0, fromIndex); 568 System.arraycopy(elements, toIndex, newElements, 569 fromIndex, numMoved); 570 setArray(newElements); 571 } 572 } finally { 573 lock.unlock(); 574 } 575 } 576 577 /** 578 * Append the element if not present. 579 * 580 * @param e element to be added to this list, if absent 581 * @return <tt>true</tt> if the element was added 582 */ 583 public boolean addIfAbsent(E e) { 584 final ReentrantLock lock = this.lock; 585 lock.lock(); 586 try { 587 // Copy while checking if already present. 588 // This wins in the most common case where it is not present 589 Object[] elements = getArray(); 590 int len = elements.length; 591 Object[] newElements = new Object[len + 1]; 592 for (int i = 0; i < len; ++i) { 593 if (eq(e, elements[i])) 594 return false; // exit, throwing away copy 595 else 596 newElements[i] = elements[i]; 597 } 598 newElements[len] = e; 599 setArray(newElements); 600 return true; 601 } finally { 602 lock.unlock(); 603 } 604 } 605 606 /** 607 * Returns <tt>true</tt> if this list contains all of the elements of the 608 * specified collection. 609 * 610 * @param c collection to be checked for containment in this list 611 * @return <tt>true</tt> if this list contains all of the elements of the 612 * specified collection 613 * @throws NullPointerException if the specified collection is null 614 * @see #contains(Object) 615 */ 616 public boolean containsAll(Collection<?> c) { 617 Object[] elements = getArray(); 618 int len = elements.length; 619 for (Object e : c) { 620 if (indexOf(e, elements, 0, len) < 0) 621 return false; 622 } 623 return true; 624 } 625 626 /** 627 * Removes from this list all of its elements that are contained in 628 * the specified collection. This is a particularly expensive operation 629 * in this class because of the need for an internal temporary array. 630 * 631 * @param c collection containing elements to be removed from this list 632 * @return <tt>true</tt> if this list changed as a result of the call 633 * @throws ClassCastException if the class of an element of this list 634 * is incompatible with the specified collection (optional) 635 * @throws NullPointerException if this list contains a null element and the 636 * specified collection does not permit null elements (optional), 637 * or if the specified collection is null 638 * @see #remove(Object) 639 */ 640 public boolean removeAll(Collection<?> c) { 641 final ReentrantLock lock = this.lock; 642 lock.lock(); 643 try { 644 Object[] elements = getArray(); 645 int len = elements.length; 646 if (len != 0) { 647 // temp array holds those elements we know we want to keep 648 int newlen = 0; 649 Object[] temp = new Object[len]; 650 for (int i = 0; i < len; ++i) { 651 Object element = elements[i]; 652 if (!c.contains(element)) 653 temp[newlen++] = element; 654 } 655 if (newlen != len) { 656 setArray(Arrays.copyOf(temp, newlen)); 657 return true; 658 } 659 } 660 return false; 661 } finally { 662 lock.unlock(); 663 } 664 } 665 666 /** 667 * Retains only the elements in this list that are contained in the 668 * specified collection. In other words, removes from this list all of 669 * its elements that are not contained in the specified collection. 670 * 671 * @param c collection containing elements to be retained in this list 672 * @return <tt>true</tt> if this list changed as a result of the call 673 * @throws ClassCastException if the class of an element of this list 674 * is incompatible with the specified collection (optional) 675 * @throws NullPointerException if this list contains a null element and the 676 * specified collection does not permit null elements (optional), 677 * or if the specified collection is null 678 * @see #remove(Object) 679 */ 680 public boolean retainAll(Collection<?> c) { 681 final ReentrantLock lock = this.lock; 682 lock.lock(); 683 try { 684 Object[] elements = getArray(); 685 int len = elements.length; 686 if (len != 0) { 687 // temp array holds those elements we know we want to keep 688 int newlen = 0; 689 Object[] temp = new Object[len]; 690 for (int i = 0; i < len; ++i) { 691 Object element = elements[i]; 692 if (c.contains(element)) 693 temp[newlen++] = element; 694 } 695 if (newlen != len) { 696 setArray(Arrays.copyOf(temp, newlen)); 697 return true; 698 } 699 } 700 return false; 701 } finally { 702 lock.unlock(); 703 } 704 } 705 706 /** 707 * Appends all of the elements in the specified collection that 708 * are not already contained in this list, to the end of 709 * this list, in the order that they are returned by the 710 * specified collection's iterator. 711 * 712 * @param c collection containing elements to be added to this list 713 * @return the number of elements added 714 * @throws NullPointerException if the specified collection is null 715 * @see #addIfAbsent(Object) 716 */ 717 public int addAllAbsent(Collection<? extends E> c) { 718 Object[] cs = c.toArray(); 719 if (cs.length == 0) 720 return 0; 721 Object[] uniq = new Object[cs.length]; 722 final ReentrantLock lock = this.lock; 723 lock.lock(); 724 try { 725 Object[] elements = getArray(); 726 int len = elements.length; 727 int added = 0; 728 for (int i = 0; i < cs.length; ++i) { // scan for duplicates 729 Object e = cs[i]; 730 if (indexOf(e, elements, 0, len) < 0 && 731 indexOf(e, uniq, 0, added) < 0) 732 uniq[added++] = e; 733 } 734 if (added > 0) { 735 Object[] newElements = Arrays.copyOf(elements, len + added); 736 System.arraycopy(uniq, 0, newElements, len, added); 737 setArray(newElements); 738 } 739 return added; 740 } finally { 741 lock.unlock(); 742 } 743 } 744 745 /** 746 * Removes all of the elements from this list. 747 * The list will be empty after this call returns. 748 */ 749 public void clear() { 750 final ReentrantLock lock = this.lock; 751 lock.lock(); 752 try { 753 setArray(new Object[0]); 754 } finally { 755 lock.unlock(); 756 } 757 } 758 759 /** 760 * Appends all of the elements in the specified collection to the end 761 * of this list, in the order that they are returned by the specified 762 * collection's iterator. 763 * 764 * @param c collection containing elements to be added to this list 765 * @return <tt>true</tt> if this list changed as a result of the call 766 * @throws NullPointerException if the specified collection is null 767 * @see #add(Object) 768 */ 769 public boolean addAll(Collection<? extends E> c) { 770 Object[] cs = c.toArray(); 771 if (cs.length == 0) 772 return false; 773 final ReentrantLock lock = this.lock; 774 lock.lock(); 775 try { 776 Object[] elements = getArray(); 777 int len = elements.length; 778 Object[] newElements = Arrays.copyOf(elements, len + cs.length); 779 System.arraycopy(cs, 0, newElements, len, cs.length); 780 setArray(newElements); 781 return true; 782 } finally { 783 lock.unlock(); 784 } 785 } 786 787 /** 788 * Inserts all of the elements in the specified collection into this 789 * list, starting at the specified position. Shifts the element 790 * currently at that position (if any) and any subsequent elements to 791 * the right (increases their indices). The new elements will appear 792 * in this list in the order that they are returned by the 793 * specified collection's iterator. 794 * 795 * @param index index at which to insert the first element 796 * from the specified collection 797 * @param c collection containing elements to be added to this list 798 * @return <tt>true</tt> if this list changed as a result of the call 799 * @throws IndexOutOfBoundsException {@inheritDoc} 800 * @throws NullPointerException if the specified collection is null 801 * @see #add(int,Object) 802 */ 803 public boolean addAll(int index, Collection<? extends E> c) { 804 Object[] cs = c.toArray(); 805 final ReentrantLock lock = this.lock; 806 lock.lock(); 807 try { 808 Object[] elements = getArray(); 809 int len = elements.length; 810 if (index > len || index < 0) 811 throw new IndexOutOfBoundsException("Index: "+index+ 812 ", Size: "+len); 813 if (cs.length == 0) 814 return false; 815 int numMoved = len - index; 816 Object[] newElements; 817 if (numMoved == 0) 818 newElements = Arrays.copyOf(elements, len + cs.length); 819 else { 820 newElements = new Object[len + cs.length]; 821 System.arraycopy(elements, 0, newElements, 0, index); 822 System.arraycopy(elements, index, 823 newElements, index + cs.length, 824 numMoved); 825 } 826 System.arraycopy(cs, 0, newElements, index, cs.length); 827 setArray(newElements); 828 return true; 829 } finally { 830 lock.unlock(); 831 } 832 } 833 834 /** 835 * Saves the state of the list to a stream (that is, serializes it). 836 * 837 * @serialData The length of the array backing the list is emitted 838 * (int), followed by all of its elements (each an Object) 839 * in the proper order. 840 * @param s the stream 841 */ 842 private void writeObject(java.io.ObjectOutputStream s) 843 throws java.io.IOException{ 844 845 s.defaultWriteObject(); 846 847 Object[] elements = getArray(); 848 // Write out array length 849 s.writeInt(elements.length); 850 851 // Write out all elements in the proper order. 852 for (Object element : elements) 853 s.writeObject(element); 854 } 855 856 /** 857 * Reconstitutes the list from a stream (that is, deserializes it). 858 * 859 * @param s the stream 860 */ 861 private void readObject(java.io.ObjectInputStream s) 862 throws java.io.IOException, ClassNotFoundException { 863 864 s.defaultReadObject(); 865 866 // bind to new lock 867 resetLock(); 868 869 // Read in array length and allocate array 870 int len = s.readInt(); 871 Object[] elements = new Object[len]; 872 873 // Read in all elements in the proper order. 874 for (int i = 0; i < len; i++) 875 elements[i] = s.readObject(); 876 setArray(elements); 877 } 878 879 /** 880 * Returns a string representation of this list. The string 881 * representation consists of the string representations of the list's 882 * elements in the order they are returned by its iterator, enclosed in 883 * square brackets (<tt>"[]"</tt>). Adjacent elements are separated by 884 * the characters <tt>", "</tt> (comma and space). Elements are 885 * converted to strings as by {@link String#valueOf(Object)}. 886 * 887 * @return a string representation of this list 888 */ 889 public String toString() { 890 return Arrays.toString(getArray()); 891 } 892 893 /** 894 * Compares the specified object with this list for equality. 895 * Returns {@code true} if the specified object is the same object 896 * as this object, or if it is also a {@link List} and the sequence 897 * of elements returned by an {@linkplain List#iterator() iterator} 898 * over the specified list is the same as the sequence returned by 899 * an iterator over this list. The two sequences are considered to 900 * be the same if they have the same length and corresponding 901 * elements at the same position in the sequence are <em>equal</em>. 902 * Two elements {@code e1} and {@code e2} are considered 903 * <em>equal</em> if {@code (e1==null ? e2==null : e1.equals(e2))}. 904 * 905 * @param o the object to be compared for equality with this list 906 * @return {@code true} if the specified object is equal to this list 907 */ 908 public boolean equals(Object o) { 909 if (o == this) 910 return true; 911 if (!(o instanceof List)) 912 return false; 913 914 List<?> list = (List<?>)(o); 915 Iterator<?> it = list.iterator(); 916 Object[] elements = getArray(); 917 int len = elements.length; 918 for (int i = 0; i < len; ++i) 919 if (!it.hasNext() || !eq(elements[i], it.next())) 920 return false; 921 if (it.hasNext()) 922 return false; 923 return true; 924 } 925 926 /** 927 * Returns the hash code value for this list. 928 * 929 * <p>This implementation uses the definition in {@link List#hashCode}. 930 * 931 * @return the hash code value for this list 932 */ 933 public int hashCode() { 934 int hashCode = 1; 935 Object[] elements = getArray(); 936 int len = elements.length; 937 for (int i = 0; i < len; ++i) { 938 Object obj = elements[i]; 939 hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode()); 940 } 941 return hashCode; 942 } 943 944 /** 945 * Returns an iterator over the elements in this list in proper sequence. 946 * 947 * <p>The returned iterator provides a snapshot of the state of the list 948 * when the iterator was constructed. No synchronization is needed while 949 * traversing the iterator. The iterator does <em>NOT</em> support the 950 * <tt>remove</tt> method. 951 * 952 * @return an iterator over the elements in this list in proper sequence 953 */ 954 public Iterator<E> iterator() { 955 return new COWIterator<E>(getArray(), 0); 956 } 957 958 /** 959 * {@inheritDoc} 960 * 961 * <p>The returned iterator provides a snapshot of the state of the list 962 * when the iterator was constructed. No synchronization is needed while 963 * traversing the iterator. The iterator does <em>NOT</em> support the 964 * <tt>remove</tt>, <tt>set</tt> or <tt>add</tt> methods. 965 */ 966 public ListIterator<E> listIterator() { 967 return new COWIterator<E>(getArray(), 0); 968 } 969 970 /** 971 * {@inheritDoc} 972 * 973 * <p>The returned iterator provides a snapshot of the state of the list 974 * when the iterator was constructed. No synchronization is needed while 975 * traversing the iterator. The iterator does <em>NOT</em> support the 976 * <tt>remove</tt>, <tt>set</tt> or <tt>add</tt> methods. 977 * 978 * @throws IndexOutOfBoundsException {@inheritDoc} 979 */ 980 public ListIterator<E> listIterator(final int index) { 981 Object[] elements = getArray(); 982 int len = elements.length; 983 if (index<0 || index>len) 984 throw new IndexOutOfBoundsException("Index: "+index); 985 986 return new COWIterator<E>(elements, index); 987 } 988 989 private static class COWIterator<E> implements ListIterator<E> { 990 /** Snapshot of the array */ 991 private final Object[] snapshot; 992 /** Index of element to be returned by subsequent call to next. */ 993 private int cursor; 994 995 private COWIterator(Object[] elements, int initialCursor) { 996 cursor = initialCursor; 997 snapshot = elements; 998 } 999 1000 public boolean hasNext() { 1001 return cursor < snapshot.length; 1002 } 1003 1004 public boolean hasPrevious() { 1005 return cursor > 0; 1006 } 1007 1008 @SuppressWarnings("unchecked") 1009 public E next() { 1010 if (! hasNext()) 1011 throw new NoSuchElementException(); 1012 return (E) snapshot[cursor++]; 1013 } 1014 1015 @SuppressWarnings("unchecked") 1016 public E previous() { 1017 if (! hasPrevious()) 1018 throw new NoSuchElementException(); 1019 return (E) snapshot[--cursor]; 1020 } 1021 1022 public int nextIndex() { 1023 return cursor; 1024 } 1025 1026 public int previousIndex() { 1027 return cursor-1; 1028 } 1029 1030 /** 1031 * Not supported. Always throws UnsupportedOperationException. 1032 * @throws UnsupportedOperationException always; <tt>remove</tt> 1033 * is not supported by this iterator. 1034 */ 1035 public void remove() { 1036 throw new UnsupportedOperationException(); 1037 } 1038 1039 /** 1040 * Not supported. Always throws UnsupportedOperationException. 1041 * @throws UnsupportedOperationException always; <tt>set</tt> 1042 * is not supported by this iterator. 1043 */ 1044 public void set(E e) { 1045 throw new UnsupportedOperationException(); 1046 } 1047 1048 /** 1049 * Not supported. Always throws UnsupportedOperationException. 1050 * @throws UnsupportedOperationException always; <tt>add</tt> 1051 * is not supported by this iterator. 1052 */ 1053 public void add(E e) { 1054 throw new UnsupportedOperationException(); 1055 } 1056 } 1057 1058 /** 1059 * Returns a view of the portion of this list between 1060 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. 1061 * The returned list is backed by this list, so changes in the 1062 * returned list are reflected in this list. 1063 * 1064 * <p>The semantics of the list returned by this method become 1065 * undefined if the backing list (i.e., this list) is modified in 1066 * any way other than via the returned list. 1067 * 1068 * @param fromIndex low endpoint (inclusive) of the subList 1069 * @param toIndex high endpoint (exclusive) of the subList 1070 * @return a view of the specified range within this list 1071 * @throws IndexOutOfBoundsException {@inheritDoc} 1072 */ 1073 public List<E> subList(int fromIndex, int toIndex) { 1074 final ReentrantLock lock = this.lock; 1075 lock.lock(); 1076 try { 1077 Object[] elements = getArray(); 1078 int len = elements.length; 1079 if (fromIndex < 0 || toIndex > len || fromIndex > toIndex) 1080 throw new IndexOutOfBoundsException(); 1081 return new COWSubList<E>(this, fromIndex, toIndex); 1082 } finally { 1083 lock.unlock(); 1084 } 1085 } 1086 1087 /** 1088 * Sublist for CopyOnWriteArrayList. 1089 * This class extends AbstractList merely for convenience, to 1090 * avoid having to define addAll, etc. This doesn't hurt, but 1091 * is wasteful. This class does not need or use modCount 1092 * mechanics in AbstractList, but does need to check for 1093 * concurrent modification using similar mechanics. On each 1094 * operation, the array that we expect the backing list to use 1095 * is checked and updated. Since we do this for all of the 1096 * base operations invoked by those defined in AbstractList, 1097 * all is well. While inefficient, this is not worth 1098 * improving. The kinds of list operations inherited from 1099 * AbstractList are already so slow on COW sublists that 1100 * adding a bit more space/time doesn't seem even noticeable. 1101 */ 1102 private static class COWSubList<E> 1103 extends AbstractList<E> 1104 implements RandomAccess 1105 { 1106 private final CopyOnWriteArrayList<E> l; 1107 private final int offset; 1108 private int size; 1109 private Object[] expectedArray; 1110 1111 // only call this holding l's lock 1112 COWSubList(CopyOnWriteArrayList<E> list, 1113 int fromIndex, int toIndex) { 1114 l = list; 1115 expectedArray = l.getArray(); 1116 offset = fromIndex; 1117 size = toIndex - fromIndex; 1118 } 1119 1120 // only call this holding l's lock 1121 private void checkForComodification() { 1122 if (l.getArray() != expectedArray) 1123 throw new ConcurrentModificationException(); 1124 } 1125 1126 // only call this holding l's lock 1127 private void rangeCheck(int index) { 1128 if (index<0 || index>=size) 1129 throw new IndexOutOfBoundsException("Index: "+index+ 1130 ",Size: "+size); 1131 } 1132 1133 public E set(int index, E element) { 1134 final ReentrantLock lock = l.lock; 1135 lock.lock(); 1136 try { 1137 rangeCheck(index); 1138 checkForComodification(); 1139 E x = l.set(index+offset, element); 1140 expectedArray = l.getArray(); 1141 return x; 1142 } finally { 1143 lock.unlock(); 1144 } 1145 } 1146 1147 public E get(int index) { 1148 final ReentrantLock lock = l.lock; 1149 lock.lock(); 1150 try { 1151 rangeCheck(index); 1152 checkForComodification(); 1153 return l.get(index+offset); 1154 } finally { 1155 lock.unlock(); 1156 } 1157 } 1158 1159 public int size() { 1160 final ReentrantLock lock = l.lock; 1161 lock.lock(); 1162 try { 1163 checkForComodification(); 1164 return size; 1165 } finally { 1166 lock.unlock(); 1167 } 1168 } 1169 1170 public void add(int index, E element) { 1171 final ReentrantLock lock = l.lock; 1172 lock.lock(); 1173 try { 1174 checkForComodification(); 1175 if (index<0 || index>size) 1176 throw new IndexOutOfBoundsException(); 1177 l.add(index+offset, element); 1178 expectedArray = l.getArray(); 1179 size++; 1180 } finally { 1181 lock.unlock(); 1182 } 1183 } 1184 1185 public void clear() { 1186 final ReentrantLock lock = l.lock; 1187 lock.lock(); 1188 try { 1189 checkForComodification(); 1190 l.removeRange(offset, offset+size); 1191 expectedArray = l.getArray(); 1192 size = 0; 1193 } finally { 1194 lock.unlock(); 1195 } 1196 } 1197 1198 public E remove(int index) { 1199 final ReentrantLock lock = l.lock; 1200 lock.lock(); 1201 try { 1202 rangeCheck(index); 1203 checkForComodification(); 1204 E result = l.remove(index+offset); 1205 expectedArray = l.getArray(); 1206 size--; 1207 return result; 1208 } finally { 1209 lock.unlock(); 1210 } 1211 } 1212 1213 public boolean remove(Object o) { 1214 int index = indexOf(o); 1215 if (index == -1) 1216 return false; 1217 remove(index); 1218 return true; 1219 } 1220 1221 public Iterator<E> iterator() { 1222 final ReentrantLock lock = l.lock; 1223 lock.lock(); 1224 try { 1225 checkForComodification(); 1226 return new COWSubListIterator<E>(l, 0, offset, size); 1227 } finally { 1228 lock.unlock(); 1229 } 1230 } 1231 1232 public ListIterator<E> listIterator(final int index) { 1233 final ReentrantLock lock = l.lock; 1234 lock.lock(); 1235 try { 1236 checkForComodification(); 1237 if (index<0 || index>size) 1238 throw new IndexOutOfBoundsException("Index: "+index+ 1239 ", Size: "+size); 1240 return new COWSubListIterator<E>(l, index, offset, size); 1241 } finally { 1242 lock.unlock(); 1243 } 1244 } 1245 1246 public List<E> subList(int fromIndex, int toIndex) { 1247 final ReentrantLock lock = l.lock; 1248 lock.lock(); 1249 try { 1250 checkForComodification(); 1251 if (fromIndex<0 || toIndex>size) 1252 throw new IndexOutOfBoundsException(); 1253 return new COWSubList<E>(l, fromIndex + offset, 1254 toIndex + offset); 1255 } finally { 1256 lock.unlock(); 1257 } 1258 } 1259 1260 } 1261 1262 1263 private static class COWSubListIterator<E> implements ListIterator<E> { 1264 private final ListIterator<E> i; 1265 private final int index; 1266 private final int offset; 1267 private final int size; 1268 1269 COWSubListIterator(List<E> l, int index, int offset, 1270 int size) { 1271 this.index = index; 1272 this.offset = offset; 1273 this.size = size; 1274 i = l.listIterator(index+offset); 1275 } 1276 1277 public boolean hasNext() { 1278 return nextIndex() < size; 1279 } 1280 1281 public E next() { 1282 if (hasNext()) 1283 return i.next(); 1284 else 1285 throw new NoSuchElementException(); 1286 } 1287 1288 public boolean hasPrevious() { 1289 return previousIndex() >= 0; 1290 } 1291 1292 public E previous() { 1293 if (hasPrevious()) 1294 return i.previous(); 1295 else 1296 throw new NoSuchElementException(); 1297 } 1298 1299 public int nextIndex() { 1300 return i.nextIndex() - offset; 1301 } 1302 1303 public int previousIndex() { 1304 return i.previousIndex() - offset; 1305 } 1306 1307 public void remove() { 1308 throw new UnsupportedOperationException(); 1309 } 1310 1311 public void set(E e) { 1312 throw new UnsupportedOperationException(); 1313 } 1314 1315 public void add(E e) { 1316 throw new UnsupportedOperationException(); 1317 } 1318 } 1319 1320 // Support for resetting lock while deserializing 1321 private void resetLock() { 1322 UNSAFE.putObjectVolatile(this, lockOffset, new ReentrantLock()); 1323 } 1324 private static final sun.misc.Unsafe UNSAFE; 1325 private static final long lockOffset; 1326 static { 1327 try { 1328 UNSAFE = sun.misc.Unsafe.getUnsafe(); 1329 Class k = CopyOnWriteArrayList.class; 1330 lockOffset = UNSAFE.objectFieldOffset 1331 (k.getDeclaredField("lock")); 1332 } catch (Exception e) { 1333 throw new Error(e); 1334 } 1335 } 1336 }