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.util.Arrays;
import java.lang.reflect.Array;
import sun.misc.Unsafe;

/**
 * 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 Unsafe unsafe;
    private static final int base;
    private static final int shift;
    private static final long arrayFieldOffset;
    private final Object[] array; // must have exact type Object[]

    static {
        try {
            unsafe = Unsafe.getUnsafe();
            arrayFieldOffset = unsafe.objectFieldOffset
                (AtomicReferenceArray.class.getDeclaredField("array"));
            base = unsafe.arrayBaseOffset(Object[].class);
            int scale = unsafe.arrayIndexScale(Object[].class);
            if ((scale & (scale - 1)) != 0)
                throw new Error("data type scale not a power of two");
            shift = 31 - Integer.numberOfLeadingZeros(scale);
        } catch (Exception 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 << shift) + base;
    }

    /**
     * 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) unsafe.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) {
        unsafe.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) {
        unsafe.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
     */
    public final E getAndSet(int i, E newValue) {
        long offset = checkedByteOffset(i);
        while (true) {
            E current = getRaw(offset);
            if (compareAndSetRaw(offset, current, newValue))
                return current;
        }
    }

    /**
     * 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 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 unsafe.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>May <a href="package-summary.html#Spurious">fail spuriously</a>
     * and does not provide ordering guarantees, 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 true if successful
     */
    public final boolean weakCompareAndSet(int i, E expect, E update) {
        return compareAndSet(i, expect, update);
    }

    /**
     * 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).
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException,
        java.io.InvalidObjectException {
        // 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);
        unsafe.putObjectVolatile(this, arrayFieldOffset, a);
    }

}
Revision:	1.3
Committed:	Sat Jan 19 20:39:43 2013 UTC (11 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+4 -5 lines
Log Message:	standardize style for arrayIndexScale checking code
#	User	Rev	Content
1	dl	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.util.Arrays;
10			import java.lang.reflect.Array;
11			import sun.misc.Unsafe;
12
13			/**
14			* An array of object references in which elements may be updated
15			* atomically. See the {@link java.util.concurrent.atomic} package
16			* specification for description of the properties of atomic
17			* variables.
18			* @since 1.5
19			* @author Doug Lea
20			* @param <E> The base class of elements held in this array
21			*/
22			public class AtomicReferenceArray<E> implements java.io.Serializable {
23			private static final long serialVersionUID = -6209656149925076980L;
24
25			private static final Unsafe unsafe;
26			private static final int base;
27			private static final int shift;
28			private static final long arrayFieldOffset;
29			private final Object[] array; // must have exact type Object[]
30
31			static {
32			try {
33			unsafe = Unsafe.getUnsafe();
34			arrayFieldOffset = unsafe.objectFieldOffset
35			(AtomicReferenceArray.class.getDeclaredField("array"));
36			base = unsafe.arrayBaseOffset(Object[].class);
37	jsr166	1.3	int scale = unsafe.arrayIndexScale(Object[].class);
38			if ((scale & (scale - 1)) != 0)
39			throw new Error("data type scale not a power of two");
40			shift = 31 - Integer.numberOfLeadingZeros(scale);
41	dl	1.1	} catch (Exception 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 << shift) + base;
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) unsafe.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			unsafe.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			unsafe.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			public final E getAndSet(int i, E newValue) {
133			long offset = checkedByteOffset(i);
134			while (true) {
135			E current = getRaw(offset);
136			if (compareAndSetRaw(offset, current, newValue))
137			return current;
138			}
139			}
140
141			/**
142			* Atomically sets the element at position {@code i} to the given
143			* updated value if the current value {@code ==} the expected value.
144			*
145			* @param i the index
146			* @param expect the expected value
147			* @param update the new value
148			* @return true if successful. False return indicates that
149			* the actual value was not equal to the expected value.
150			*/
151			public final boolean compareAndSet(int i, E expect, E update) {
152			return compareAndSetRaw(checkedByteOffset(i), expect, update);
153			}
154
155			private boolean compareAndSetRaw(long offset, E expect, E update) {
156			return unsafe.compareAndSwapObject(array, offset, expect, update);
157			}
158
159			/**
160			* Atomically sets the element at position {@code i} to the given
161			* updated value if the current value {@code ==} the expected value.
162			*
163			* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
164			* and does not provide ordering guarantees, so is only rarely an
165			* appropriate alternative to {@code compareAndSet}.
166			*
167			* @param i the index
168			* @param expect the expected value
169			* @param update the new value
170	jsr166	1.2	* @return true if successful
171	dl	1.1	*/
172			public final boolean weakCompareAndSet(int i, E expect, E update) {
173			return compareAndSet(i, expect, update);
174			}
175
176			/**
177			* Returns the String representation of the current values of array.
178			* @return the String representation of the current values of array
179			*/
180			public String toString() {
181			int iMax = array.length - 1;
182			if (iMax == -1)
183			return "[]";
184
185			StringBuilder b = new StringBuilder();
186			b.append('[');
187			for (int i = 0; ; i++) {
188			b.append(getRaw(byteOffset(i)));
189			if (i == iMax)
190			return b.append(']').toString();
191			b.append(',').append(' ');
192			}
193			}
194
195			/**
196			* Reconstitutes the instance from a stream (that is, deserializes it).
197			*/
198			private void readObject(java.io.ObjectInputStream s)
199			throws java.io.IOException, ClassNotFoundException,
200			java.io.InvalidObjectException {
201			// Note: This must be changed if any additional fields are defined
202			Object a = s.readFields().get("array", null);
203			if (a == null \|\| !a.getClass().isArray())
204			throw new java.io.InvalidObjectException("Not array type");
205			if (a.getClass() != Object[].class)
206			a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);
207			unsafe.putObjectVolatile(this, arrayFieldOffset, a);
208			}
209
210			}