| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent.atomic; |
| |
| import java.lang.reflect.Array; |
| import java.util.Arrays; |
| import java.util.function.BinaryOperator; |
| import java.util.function.UnaryOperator; |
| |
| /** |
| * An array of object references in which elements may be updated |
| * atomically. See the {@link java.util.concurrent.atomic} package |
| * specification for description of the properties of atomic |
| * variables. |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <E> The base class of elements held in this array |
| */ |
| public class AtomicReferenceArray<E> implements java.io.Serializable { |
| private static final long serialVersionUID = -6209656149925076980L; |
| |
| private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe(); |
| private static final long ARRAY; |
| private static final int ABASE; |
| private static final int ASHIFT; |
| private final Object[] array; // must have exact type Object[] |
| |
| static { |
| try { |
| ARRAY = U.objectFieldOffset |
| (AtomicReferenceArray.class.getDeclaredField("array")); |
| ABASE = U.arrayBaseOffset(Object[].class); |
| int scale = U.arrayIndexScale(Object[].class); |
| if ((scale & (scale - 1)) != 0) |
| throw new Error("array index scale not a power of two"); |
| ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); |
| } catch (ReflectiveOperationException e) { |
| throw new Error(e); |
| } |
| } |
| |
| private long checkedByteOffset(int i) { |
| if (i < 0 || i >= array.length) |
| throw new IndexOutOfBoundsException("index " + i); |
| |
| return byteOffset(i); |
| } |
| |
| private static long byteOffset(int i) { |
| return ((long) i << ASHIFT) + ABASE; |
| } |
| |
| /** |
| * Creates a new AtomicReferenceArray of the given length, with all |
| * elements initially null. |
| * |
| * @param length the length of the array |
| */ |
| public AtomicReferenceArray(int length) { |
| array = new Object[length]; |
| } |
| |
| /** |
| * Creates a new AtomicReferenceArray with the same length as, and |
| * all elements copied from, the given array. |
| * |
| * @param array the array to copy elements from |
| * @throws NullPointerException if array is null |
| */ |
| public AtomicReferenceArray(E[] array) { |
| // Visibility guaranteed by final field guarantees |
| this.array = Arrays.copyOf(array, array.length, Object[].class); |
| } |
| |
| /** |
| * Returns the length of the array. |
| * |
| * @return the length of the array |
| */ |
| public final int length() { |
| return array.length; |
| } |
| |
| /** |
| * Gets the current value at position {@code i}. |
| * |
| * @param i the index |
| * @return the current value |
| */ |
| public final E get(int i) { |
| return getRaw(checkedByteOffset(i)); |
| } |
| |
| @SuppressWarnings("unchecked") |
| private E getRaw(long offset) { |
| return (E) U.getObjectVolatile(array, offset); |
| } |
| |
| /** |
| * Sets the element at position {@code i} to the given value. |
| * |
| * @param i the index |
| * @param newValue the new value |
| */ |
| public final void set(int i, E newValue) { |
| U.putObjectVolatile(array, checkedByteOffset(i), newValue); |
| } |
| |
| /** |
| * Eventually sets the element at position {@code i} to the given value. |
| * |
| * @param i the index |
| * @param newValue the new value |
| * @since 1.6 |
| */ |
| public final void lazySet(int i, E newValue) { |
| U.putOrderedObject(array, checkedByteOffset(i), newValue); |
| } |
| |
| /** |
| * Atomically sets the element at position {@code i} to the given |
| * value and returns the old value. |
| * |
| * @param i the index |
| * @param newValue the new value |
| * @return the previous value |
| */ |
| @SuppressWarnings("unchecked") |
| public final E getAndSet(int i, E newValue) { |
| return (E)U.getAndSetObject(array, checkedByteOffset(i), newValue); |
| } |
| |
| /** |
| * Atomically sets the element at position {@code i} to the given |
| * updated value if the current value {@code ==} the expected value. |
| * |
| * @param i the index |
| * @param expect the expected value |
| * @param update the new value |
| * @return {@code true} if successful. False return indicates that |
| * the actual value was not equal to the expected value. |
| */ |
| public final boolean compareAndSet(int i, E expect, E update) { |
| return compareAndSetRaw(checkedByteOffset(i), expect, update); |
| } |
| |
| private boolean compareAndSetRaw(long offset, E expect, E update) { |
| return U.compareAndSwapObject(array, offset, expect, update); |
| } |
| |
| /** |
| * Atomically sets the element at position {@code i} to the given |
| * updated value if the current value {@code ==} the expected value. |
| * |
| * <p><a href="package-summary.html#weakCompareAndSet">May fail |
| * spuriously and does not provide ordering guarantees</a>, so is |
| * only rarely an appropriate alternative to {@code compareAndSet}. |
| * |
| * @param i the index |
| * @param expect the expected value |
| * @param update the new value |
| * @return {@code true} if successful |
| */ |
| public final boolean weakCompareAndSet(int i, E expect, E update) { |
| return compareAndSet(i, expect, update); |
| } |
| |
| /** |
| * Atomically updates the element at index {@code i} with the results |
| * of applying the given function, returning the previous value. The |
| * function should be side-effect-free, since it may be re-applied |
| * when attempted updates fail due to contention among threads. |
| * |
| * @param i the index |
| * @param updateFunction a side-effect-free function |
| * @return the previous value |
| * @since 1.8 |
| */ |
| public final E getAndUpdate(int i, UnaryOperator<E> updateFunction) { |
| long offset = checkedByteOffset(i); |
| E prev, next; |
| do { |
| prev = getRaw(offset); |
| next = updateFunction.apply(prev); |
| } while (!compareAndSetRaw(offset, prev, next)); |
| return prev; |
| } |
| |
| /** |
| * Atomically updates the element at index {@code i} with the results |
| * of applying the given function, returning the updated value. The |
| * function should be side-effect-free, since it may be re-applied |
| * when attempted updates fail due to contention among threads. |
| * |
| * @param i the index |
| * @param updateFunction a side-effect-free function |
| * @return the updated value |
| * @since 1.8 |
| */ |
| public final E updateAndGet(int i, UnaryOperator<E> updateFunction) { |
| long offset = checkedByteOffset(i); |
| E prev, next; |
| do { |
| prev = getRaw(offset); |
| next = updateFunction.apply(prev); |
| } while (!compareAndSetRaw(offset, prev, next)); |
| return next; |
| } |
| |
| /** |
| * Atomically updates the element at index {@code i} with the |
| * results of applying the given function to the current and |
| * given values, returning the previous value. The function should |
| * be side-effect-free, since it may be re-applied when attempted |
| * updates fail due to contention among threads. The function is |
| * applied with the current value at index {@code i} as its first |
| * argument, and the given update as the second argument. |
| * |
| * @param i the index |
| * @param x the update value |
| * @param accumulatorFunction a side-effect-free function of two arguments |
| * @return the previous value |
| * @since 1.8 |
| */ |
| public final E getAndAccumulate(int i, E x, |
| BinaryOperator<E> accumulatorFunction) { |
| long offset = checkedByteOffset(i); |
| E prev, next; |
| do { |
| prev = getRaw(offset); |
| next = accumulatorFunction.apply(prev, x); |
| } while (!compareAndSetRaw(offset, prev, next)); |
| return prev; |
| } |
| |
| /** |
| * Atomically updates the element at index {@code i} with the |
| * results of applying the given function to the current and |
| * given values, returning the updated value. The function should |
| * be side-effect-free, since it may be re-applied when attempted |
| * updates fail due to contention among threads. The function is |
| * applied with the current value at index {@code i} as its first |
| * argument, and the given update as the second argument. |
| * |
| * @param i the index |
| * @param x the update value |
| * @param accumulatorFunction a side-effect-free function of two arguments |
| * @return the updated value |
| * @since 1.8 |
| */ |
| public final E accumulateAndGet(int i, E x, |
| BinaryOperator<E> accumulatorFunction) { |
| long offset = checkedByteOffset(i); |
| E prev, next; |
| do { |
| prev = getRaw(offset); |
| next = accumulatorFunction.apply(prev, x); |
| } while (!compareAndSetRaw(offset, prev, next)); |
| return next; |
| } |
| |
| /** |
| * Returns the String representation of the current values of array. |
| * @return the String representation of the current values of array |
| */ |
| public String toString() { |
| int iMax = array.length - 1; |
| if (iMax == -1) |
| return "[]"; |
| |
| StringBuilder b = new StringBuilder(); |
| b.append('['); |
| for (int i = 0; ; i++) { |
| b.append(getRaw(byteOffset(i))); |
| if (i == iMax) |
| return b.append(']').toString(); |
| b.append(',').append(' '); |
| } |
| } |
| |
| /** |
| * Reconstitutes the instance from a stream (that is, deserializes it). |
| * @param s the stream |
| * @throws ClassNotFoundException if the class of a serialized object |
| * could not be found |
| * @throws java.io.IOException if an I/O error occurs |
| */ |
| private void readObject(java.io.ObjectInputStream s) |
| throws java.io.IOException, ClassNotFoundException { |
| // Note: This must be changed if any additional fields are defined |
| Object a = s.readFields().get("array", null); |
| if (a == null || !a.getClass().isArray()) |
| throw new java.io.InvalidObjectException("Not array type"); |
| if (a.getClass() != Object[].class) |
| a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class); |
| U.putObjectVolatile(this, ARRAY, a); |
| } |
| |
| } |