concurrent/atomic/AtomicReferenceArray.java

/*
 * 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);
    }

}
Revision:	1.1
Committed:	Sat Mar 26 06:22:51 2016 UTC (8 years, 1 month ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent.atomic;
8
9	import java.lang.reflect.Array;
10	import java.util.Arrays;
11	import java.util.function.BinaryOperator;
12	import java.util.function.UnaryOperator;
13
14	/**
15	* An array of object references in which elements may be updated
16	* atomically. See the {@link java.util.concurrent.atomic} package
17	* specification for description of the properties of atomic
18	* variables.
19	* @since 1.5
20	* @author Doug Lea
21	* @param <E> The base class of elements held in this array
22	*/
23	public class AtomicReferenceArray<E> implements java.io.Serializable {
24	private static final long serialVersionUID = -6209656149925076980L;
25
26	private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
27	private static final long ARRAY;
28	private static final int ABASE;
29	private static final int ASHIFT;
30	private final Object[] array; // must have exact type Object[]
31
32	static {
33	try {
34	ARRAY = U.objectFieldOffset
35	(AtomicReferenceArray.class.getDeclaredField("array"));
36	ABASE = U.arrayBaseOffset(Object[].class);
37	int scale = U.arrayIndexScale(Object[].class);
38	if ((scale & (scale - 1)) != 0)
39	throw new Error("array index scale not a power of two");
40	ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
41	} catch (ReflectiveOperationException e) {
42	throw new Error(e);
43	}
44	}
45
46	private long checkedByteOffset(int i) {
47	if (i < 0 \|\| i >= array.length)
48	throw new IndexOutOfBoundsException("index " + i);
49
50	return byteOffset(i);
51	}
52
53	private static long byteOffset(int i) {
54	return ((long) i << ASHIFT) + ABASE;
55	}
56
57	/**
58	* Creates a new AtomicReferenceArray of the given length, with all
59	* elements initially null.
60	*
61	* @param length the length of the array
62	*/
63	public AtomicReferenceArray(int length) {
64	array = new Object[length];
65	}
66
67	/**
68	* Creates a new AtomicReferenceArray with the same length as, and
69	* all elements copied from, the given array.
70	*
71	* @param array the array to copy elements from
72	* @throws NullPointerException if array is null
73	*/
74	public AtomicReferenceArray(E[] array) {
75	// Visibility guaranteed by final field guarantees
76	this.array = Arrays.copyOf(array, array.length, Object[].class);
77	}
78
79	/**
80	* Returns the length of the array.
81	*
82	* @return the length of the array
83	*/
84	public final int length() {
85	return array.length;
86	}
87
88	/**
89	* Gets the current value at position {@code i}.
90	*
91	* @param i the index
92	* @return the current value
93	*/
94	public final E get(int i) {
95	return getRaw(checkedByteOffset(i));
96	}
97
98	@SuppressWarnings("unchecked")
99	private E getRaw(long offset) {
100	return (E) U.getObjectVolatile(array, offset);
101	}
102
103	/**
104	* Sets the element at position {@code i} to the given value.
105	*
106	* @param i the index
107	* @param newValue the new value
108	*/
109	public final void set(int i, E newValue) {
110	U.putObjectVolatile(array, checkedByteOffset(i), newValue);
111	}
112
113	/**
114	* Eventually sets the element at position {@code i} to the given value.
115	*
116	* @param i the index
117	* @param newValue the new value
118	* @since 1.6
119	*/
120	public final void lazySet(int i, E newValue) {
121	U.putOrderedObject(array, checkedByteOffset(i), newValue);
122	}
123
124	/**
125	* Atomically sets the element at position {@code i} to the given
126	* value and returns the old value.
127	*
128	* @param i the index
129	* @param newValue the new value
130	* @return the previous value
131	*/
132	@SuppressWarnings("unchecked")
133	public final E getAndSet(int i, E newValue) {
134	return (E)U.getAndSetObject(array, checkedByteOffset(i), newValue);
135	}
136
137	/**
138	* Atomically sets the element at position {@code i} to the given
139	* updated value if the current value {@code ==} the expected value.
140	*
141	* @param i the index
142	* @param expect the expected value
143	* @param update the new value
144	* @return {@code true} if successful. False return indicates that
145	* the actual value was not equal to the expected value.
146	*/
147	public final boolean compareAndSet(int i, E expect, E update) {
148	return compareAndSetRaw(checkedByteOffset(i), expect, update);
149	}
150
151	private boolean compareAndSetRaw(long offset, E expect, E update) {
152	return U.compareAndSwapObject(array, offset, expect, update);
153	}
154
155	/**
156	* Atomically sets the element at position {@code i} to the given
157	* updated value if the current value {@code ==} the expected value.
158	*
159	* <p><a href="package-summary.html#weakCompareAndSet">May fail
160	* spuriously and does not provide ordering guarantees</a>, so is
161	* only rarely an appropriate alternative to {@code compareAndSet}.
162	*
163	* @param i the index
164	* @param expect the expected value
165	* @param update the new value
166	* @return {@code true} if successful
167	*/
168	public final boolean weakCompareAndSet(int i, E expect, E update) {
169	return compareAndSet(i, expect, update);
170	}
171
172	/**
173	* Atomically updates the element at index {@code i} with the results
174	* of applying the given function, returning the previous value. The
175	* function should be side-effect-free, since it may be re-applied
176	* when attempted updates fail due to contention among threads.
177	*
178	* @param i the index
179	* @param updateFunction a side-effect-free function
180	* @return the previous value
181	* @since 1.8
182	*/
183	public final E getAndUpdate(int i, UnaryOperator<E> updateFunction) {
184	long offset = checkedByteOffset(i);
185	E prev, next;
186	do {
187	prev = getRaw(offset);
188	next = updateFunction.apply(prev);
189	} while (!compareAndSetRaw(offset, prev, next));
190	return prev;
191	}
192
193	/**
194	* Atomically updates the element at index {@code i} with the results
195	* of applying the given function, returning the updated value. The
196	* function should be side-effect-free, since it may be re-applied
197	* when attempted updates fail due to contention among threads.
198	*
199	* @param i the index
200	* @param updateFunction a side-effect-free function
201	* @return the updated value
202	* @since 1.8
203	*/
204	public final E updateAndGet(int i, UnaryOperator<E> updateFunction) {
205	long offset = checkedByteOffset(i);
206	E prev, next;
207	do {
208	prev = getRaw(offset);
209	next = updateFunction.apply(prev);
210	} while (!compareAndSetRaw(offset, prev, next));
211	return next;
212	}
213
214	/**
215	* Atomically updates the element at index {@code i} with the
216	* results of applying the given function to the current and
217	* given values, returning the previous value. The function should
218	* be side-effect-free, since it may be re-applied when attempted
219	* updates fail due to contention among threads. The function is
220	* applied with the current value at index {@code i} as its first
221	* argument, and the given update as the second argument.
222	*
223	* @param i the index
224	* @param x the update value
225	* @param accumulatorFunction a side-effect-free function of two arguments
226	* @return the previous value
227	* @since 1.8
228	*/
229	public final E getAndAccumulate(int i, E x,
230	BinaryOperator<E> accumulatorFunction) {
231	long offset = checkedByteOffset(i);
232	E prev, next;
233	do {
234	prev = getRaw(offset);
235	next = accumulatorFunction.apply(prev, x);
236	} while (!compareAndSetRaw(offset, prev, next));
237	return prev;
238	}
239
240	/**
241	* Atomically updates the element at index {@code i} with the
242	* results of applying the given function to the current and
243	* given values, returning the updated value. The function should
244	* be side-effect-free, since it may be re-applied when attempted
245	* updates fail due to contention among threads. The function is
246	* applied with the current value at index {@code i} as its first
247	* argument, and the given update as the second argument.
248	*
249	* @param i the index
250	* @param x the update value
251	* @param accumulatorFunction a side-effect-free function of two arguments
252	* @return the updated value
253	* @since 1.8
254	*/
255	public final E accumulateAndGet(int i, E x,
256	BinaryOperator<E> accumulatorFunction) {
257	long offset = checkedByteOffset(i);
258	E prev, next;
259	do {
260	prev = getRaw(offset);
261	next = accumulatorFunction.apply(prev, x);
262	} while (!compareAndSetRaw(offset, prev, next));
263	return next;
264	}
265
266	/**
267	* Returns the String representation of the current values of array.
268	* @return the String representation of the current values of array
269	*/
270	public String toString() {
271	int iMax = array.length - 1;
272	if (iMax == -1)
273	return "[]";
274
275	StringBuilder b = new StringBuilder();
276	b.append('[');
277	for (int i = 0; ; i++) {
278	b.append(getRaw(byteOffset(i)));
279	if (i == iMax)
280	return b.append(']').toString();
281	b.append(',').append(' ');
282	}
283	}
284
285	/**
286	* Reconstitutes the instance from a stream (that is, deserializes it).
287	* @param s the stream
288	* @throws ClassNotFoundException if the class of a serialized object
289	* could not be found
290	* @throws java.io.IOException if an I/O error occurs
291	*/
292	private void readObject(java.io.ObjectInputStream s)
293	throws java.io.IOException, ClassNotFoundException {
294	// Note: This must be changed if any additional fields are defined
295	Object a = s.readFields().get("array", null);
296	if (a == null \|\| !a.getClass().isArray())
297	throw new java.io.InvalidObjectException("Not array type");
298	if (a.getClass() != Object[].class)
299	a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);
300	U.putObjectVolatile(this, ARRAY, a);
301	}
302
303	}