author | dl |
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parent 5506 | 202f599c92aa |
child 9242 | ef138d47df58 |
permissions | -rw-r--r-- |
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/* |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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/* |
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* This file is available under and governed by the GNU General Public |
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* License version 2 only, as published by the Free Software Foundation. |
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* However, the following notice accompanied the original version of this |
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* file: |
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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/licenses/publicdomain |
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*/ |
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package java.util.concurrent.atomic; |
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import sun.misc.Unsafe; |
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import java.util.*; |
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/** |
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* An array of object references in which elements may be updated |
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* atomically. See the {@link java.util.concurrent.atomic} package |
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* specification for description of the properties of atomic |
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* variables. |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <E> The base class of elements held in this array |
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*/ |
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public class AtomicReferenceArray<E> implements java.io.Serializable { |
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private static final long serialVersionUID = -6209656149925076980L; |
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private static final Unsafe unsafe = Unsafe.getUnsafe(); |
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private static final int base = unsafe.arrayBaseOffset(Object[].class); |
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private static final int shift; |
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private final Object[] array; |
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static { |
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int scale = unsafe.arrayIndexScale(Object[].class); |
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if ((scale & (scale - 1)) != 0) |
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throw new Error("data type scale not a power of two"); |
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shift = 31 - Integer.numberOfLeadingZeros(scale); |
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} |
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private long checkedByteOffset(int i) { |
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if (i < 0 || i >= array.length) |
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throw new IndexOutOfBoundsException("index " + i); |
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return byteOffset(i); |
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} |
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private static long byteOffset(int i) { |
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return ((long) i << shift) + base; |
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} |
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/** |
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* Creates a new AtomicReferenceArray of the given length, with all |
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* elements initially null. |
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* |
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* @param length the length of the array |
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*/ |
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public AtomicReferenceArray(int length) { |
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array = new Object[length]; |
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} |
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/** |
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* Creates a new AtomicReferenceArray with the same length as, and |
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* all elements copied from, the given array. |
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* |
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* @param array the array to copy elements from |
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* @throws NullPointerException if array is null |
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*/ |
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public AtomicReferenceArray(E[] array) { |
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// Visibility guaranteed by final field guarantees |
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this.array = array.clone(); |
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} |
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/** |
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* Returns the length of the array. |
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* |
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* @return the length of the array |
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*/ |
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public final int length() { |
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return array.length; |
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} |
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/** |
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* Gets the current value at position {@code i}. |
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* |
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* @param i the index |
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* @return the current value |
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*/ |
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public final E get(int i) { |
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return getRaw(checkedByteOffset(i)); |
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} |
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private E getRaw(long offset) { |
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return (E) unsafe.getObjectVolatile(array, offset); |
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} |
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/** |
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* Sets the element at position {@code i} to the given value. |
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* |
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* @param i the index |
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* @param newValue the new value |
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*/ |
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public final void set(int i, E newValue) { |
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unsafe.putObjectVolatile(array, checkedByteOffset(i), newValue); |
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} |
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/** |
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* Eventually sets the element at position {@code i} to the given value. |
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* |
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* @param i the index |
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* @param newValue the new value |
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* @since 1.6 |
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*/ |
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public final void lazySet(int i, E newValue) { |
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unsafe.putOrderedObject(array, checkedByteOffset(i), newValue); |
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} |
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/** |
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* Atomically sets the element at position {@code i} to the given |
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* value and returns the old value. |
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* |
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* @param i the index |
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* @param newValue the new value |
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* @return the previous value |
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*/ |
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public final E getAndSet(int i, E newValue) { |
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long offset = checkedByteOffset(i); |
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while (true) { |
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E current = (E) getRaw(offset); |
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if (compareAndSetRaw(offset, current, newValue)) |
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return current; |
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} |
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} |
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/** |
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* Atomically sets the element at position {@code i} to the given |
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* updated value if the current value {@code ==} the expected value. |
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* |
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* @param i the index |
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* @param expect the expected value |
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* @param update the new value |
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* @return true if successful. False return indicates that |
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* the actual value was not equal to the expected value. |
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*/ |
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public final boolean compareAndSet(int i, E expect, E update) { |
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return compareAndSetRaw(checkedByteOffset(i), expect, update); |
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} |
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private boolean compareAndSetRaw(long offset, E expect, E update) { |
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return unsafe.compareAndSwapObject(array, offset, expect, update); |
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} |
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/** |
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* Atomically sets the element at position {@code i} to the given |
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* updated value if the current value {@code ==} the expected value. |
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* |
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* <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
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* and does not provide ordering guarantees, so is only rarely an |
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* appropriate alternative to {@code compareAndSet}. |
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* |
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* @param i the index |
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* @param expect the expected value |
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* @param update the new value |
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* @return true if successful. |
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*/ |
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public final boolean weakCompareAndSet(int i, E expect, E update) { |
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return compareAndSet(i, expect, update); |
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} |
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/** |
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* Returns the String representation of the current values of array. |
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* @return the String representation of the current values of array |
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*/ |
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public String toString() { |
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int iMax = array.length - 1; |
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if (iMax == -1) |
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return "[]"; |
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StringBuilder b = new StringBuilder(); |
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b.append('['); |
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for (int i = 0; ; i++) { |
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b.append(getRaw(byteOffset(i))); |
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if (i == iMax) |
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return b.append(']').toString(); |
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b.append(',').append(' '); |
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} |
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} |
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} |