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, 2 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	User	Rev	Content
1	jsr166	1.1	/*
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			}