jsr166e/extra/AtomicDoubleArray.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 jsr166e.extra;

import static java.lang.Double.doubleToRawLongBits;
import static java.lang.Double.longBitsToDouble;

/**
 * A {@code double} array in which elements may be updated atomically.
 * See the {@link java.util.concurrent.atomic} package specification
 * for description of the properties of atomic variables.
 *
 * <p><a name="bitEquals">This class compares primitive {@code double}
 * values in methods such as {@link #compareAndSet} by comparing their
 * bitwise representation using {@link Double#doubleToRawLongBits},
 * which differs from both the primitive double {@code ==} operator
 * and from {@link Double#equals}, as if implemented by:
 *  <pre> {@code
 * boolean bitEquals(double x, double y) {
 *   long xBits = Double.doubleToRawLongBits(x);
 *   long yBits = Double.doubleToRawLongBits(y);
 *   return xBits == yBits;
 * }}</pre>
 *
 * @author Doug Lea
 * @author Martin Buchholz
 */
public class AtomicDoubleArray implements java.io.Serializable {
    private static final long serialVersionUID = -2308431214976778248L;

    private final long[] array;

    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 {@code AtomicDoubleArray} of the given length,
     * with all elements initially zero.
     *
     * @param length the length of the array
     */
    public AtomicDoubleArray(int length) {
        array = new long[length];
    }

    /**
     * Creates a new {@code AtomicDoubleArray} 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 AtomicDoubleArray(double[] array) {
        // Visibility guaranteed by final field guarantees
        final int len = array.length;
        final long[] a = new long[len];
        for (int i = 0; i < len; i++)
            a[i] = doubleToRawLongBits(array[i]);
        this.array = a;
    }

    /**
     * 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 double get(int i) {
        return longBitsToDouble(getRaw(checkedByteOffset(i)));
    }

    private long getRaw(long offset) {
        return unsafe.getLongVolatile(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, double newValue) {
        long next = doubleToRawLongBits(newValue);
        unsafe.putLongVolatile(array, checkedByteOffset(i), next);
    }

    /**
     * Eventually sets the element at position {@code i} to the given value.
     *
     * @param i the index
     * @param newValue the new value
     */
    public final void lazySet(int i, double newValue) {
        long next = doubleToRawLongBits(newValue);
        unsafe.putOrderedLong(array, checkedByteOffset(i), next);
    }

    /**
     * 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 double getAndSet(int i, double newValue) {
        long next = doubleToRawLongBits(newValue);
        long offset = checkedByteOffset(i);
        while (true) {
            long current = getRaw(offset);
            if (compareAndSetRaw(offset, current, next))
                return longBitsToDouble(current);
        }
    }

    /**
     * Atomically sets the element at position {@code i} to the given
     * updated value
     * if the current value is <a href="#bitEquals">bitwise equal</a>
     * to 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, double expect, double update) {
        return compareAndSetRaw(checkedByteOffset(i),
                                doubleToRawLongBits(expect),
                                doubleToRawLongBits(update));
    }

    private boolean compareAndSetRaw(long offset, long expect, long update) {
        return unsafe.compareAndSwapLong(array, offset, expect, update);
    }

    /**
     * Atomically sets the element at position {@code i} to the given
     * updated value
     * if the current value is <a href="#bitEquals">bitwise equal</a>
     * to 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, double expect, double update) {
        return compareAndSet(i, expect, update);
    }

    /**
     * Atomically adds the given value to the element at index {@code i}.
     *
     * @param i the index
     * @param delta the value to add
     * @return the previous value
     */
    public final double getAndAdd(int i, double delta) {
        long offset = checkedByteOffset(i);
        while (true) {
            long current = getRaw(offset);
            double currentVal = longBitsToDouble(current);
            double nextVal = currentVal + delta;
            long next = doubleToRawLongBits(nextVal);
            if (compareAndSetRaw(offset, current, next))
                return currentVal;
        }
    }

    /**
     * Atomically adds the given value to the element at index {@code i}.
     *
     * @param i the index
     * @param delta the value to add
     * @return the updated value
     */
    public double addAndGet(int i, double delta) {
        long offset = checkedByteOffset(i);
        while (true) {
            long current = getRaw(offset);
            double currentVal = longBitsToDouble(current);
            double nextVal = currentVal + delta;
            long next = doubleToRawLongBits(nextVal);
            if (compareAndSetRaw(offset, current, next))
                return nextVal;
        }
    }

    /**
     * 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(longBitsToDouble(getRaw(byteOffset(i))));
            if (i == iMax)
                return b.append(']').toString();
            b.append(',').append(' ');
        }
    }

    // Unsafe mechanics
    private static final sun.misc.Unsafe unsafe = getUnsafe();
    private static final int base = unsafe.arrayBaseOffset(long[].class);
    private static final int shift;

    static {
        int scale = unsafe.arrayIndexScale(long[].class);
        if ((scale & (scale - 1)) != 0)
            throw new Error("data type scale not a power of two");
        shift = 31 - Integer.numberOfLeadingZeros(scale);
    }

    /**
     * Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
     * Replace with a simple call to Unsafe.getUnsafe when integrating
     * into a jdk.
     *
     * @return a sun.misc.Unsafe
     */
    private static sun.misc.Unsafe getUnsafe() {
        try {
            return sun.misc.Unsafe.getUnsafe();
        } catch (SecurityException se) {
            try {
                return java.security.AccessController.doPrivileged
                    (new java.security
                     .PrivilegedExceptionAction<sun.misc.Unsafe>() {
                        public sun.misc.Unsafe run() throws Exception {
                            java.lang.reflect.Field f = sun.misc
                                .Unsafe.class.getDeclaredField("theUnsafe");
                            f.setAccessible(true);
                            return (sun.misc.Unsafe) f.get(null);
                        }});
            } catch (java.security.PrivilegedActionException e) {
                throw new RuntimeException("Could not initialize intrinsics",
                                           e.getCause());
            }
        }
    }
}
Revision:	1.1
Committed:	Wed Aug 10 02:03:29 2011 UTC (12 years, 10 months ago) by jsr166
Branch:	MAIN
Log Message:	release early; release often
#	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 jsr166e.extra;
8
9			import static java.lang.Double.doubleToRawLongBits;
10			import static java.lang.Double.longBitsToDouble;
11
12			/**
13			* A {@code double} array in which elements may be updated atomically.
14			* See the {@link java.util.concurrent.atomic} package specification
15			* for description of the properties of atomic variables.
16			*
17			* <p><a name="bitEquals">This class compares primitive {@code double}
18			* values in methods such as {@link #compareAndSet} by comparing their
19			* bitwise representation using {@link Double#doubleToRawLongBits},
20			* which differs from both the primitive double {@code ==} operator
21			* and from {@link Double#equals}, as if implemented by:
22			* <pre> {@code
23			* boolean bitEquals(double x, double y) {
24			* long xBits = Double.doubleToRawLongBits(x);
25			* long yBits = Double.doubleToRawLongBits(y);
26			* return xBits == yBits;
27			* }}</pre>
28			*
29			* @author Doug Lea
30			* @author Martin Buchholz
31			*/
32			public class AtomicDoubleArray implements java.io.Serializable {
33			private static final long serialVersionUID = -2308431214976778248L;
34
35			private final long[] array;
36
37			private long checkedByteOffset(int i) {
38			if (i < 0 \|\| i >= array.length)
39			throw new IndexOutOfBoundsException("index " + i);
40
41			return byteOffset(i);
42			}
43
44			private static long byteOffset(int i) {
45			return ((long) i << shift) + base;
46			}
47
48			/**
49			* Creates a new {@code AtomicDoubleArray} of the given length,
50			* with all elements initially zero.
51			*
52			* @param length the length of the array
53			*/
54			public AtomicDoubleArray(int length) {
55			array = new long[length];
56			}
57
58			/**
59			* Creates a new {@code AtomicDoubleArray} with the same length
60			* as, and all elements copied from, the given array.
61			*
62			* @param array the array to copy elements from
63			* @throws NullPointerException if array is null
64			*/
65			public AtomicDoubleArray(double[] array) {
66			// Visibility guaranteed by final field guarantees
67			final int len = array.length;
68			final long[] a = new long[len];
69			for (int i = 0; i < len; i++)
70			a[i] = doubleToRawLongBits(array[i]);
71			this.array = a;
72			}
73
74			/**
75			* Returns the length of the array.
76			*
77			* @return the length of the array
78			*/
79			public final int length() {
80			return array.length;
81			}
82
83			/**
84			* Gets the current value at position {@code i}.
85			*
86			* @param i the index
87			* @return the current value
88			*/
89			public final double get(int i) {
90			return longBitsToDouble(getRaw(checkedByteOffset(i)));
91			}
92
93			private long getRaw(long offset) {
94			return unsafe.getLongVolatile(array, offset);
95			}
96
97			/**
98			* Sets the element at position {@code i} to the given value.
99			*
100			* @param i the index
101			* @param newValue the new value
102			*/
103			public final void set(int i, double newValue) {
104			long next = doubleToRawLongBits(newValue);
105			unsafe.putLongVolatile(array, checkedByteOffset(i), next);
106			}
107
108			/**
109			* Eventually sets the element at position {@code i} to the given value.
110			*
111			* @param i the index
112			* @param newValue the new value
113			*/
114			public final void lazySet(int i, double newValue) {
115			long next = doubleToRawLongBits(newValue);
116			unsafe.putOrderedLong(array, checkedByteOffset(i), next);
117			}
118
119			/**
120			* Atomically sets the element at position {@code i} to the given value
121			* and returns the old value.
122			*
123			* @param i the index
124			* @param newValue the new value
125			* @return the previous value
126			*/
127			public final double getAndSet(int i, double newValue) {
128			long next = doubleToRawLongBits(newValue);
129			long offset = checkedByteOffset(i);
130			while (true) {
131			long current = getRaw(offset);
132			if (compareAndSetRaw(offset, current, next))
133			return longBitsToDouble(current);
134			}
135			}
136
137			/**
138			* Atomically sets the element at position {@code i} to the given
139			* updated value
140			* if the current value is <a href="#bitEquals">bitwise equal</a>
141			* to the expected value.
142			*
143			* @param i the index
144			* @param expect the expected value
145			* @param update the new value
146			* @return true if successful. False return indicates that
147			* the actual value was not equal to the expected value.
148			*/
149			public final boolean compareAndSet(int i, double expect, double update) {
150			return compareAndSetRaw(checkedByteOffset(i),
151			doubleToRawLongBits(expect),
152			doubleToRawLongBits(update));
153			}
154
155			private boolean compareAndSetRaw(long offset, long expect, long update) {
156			return unsafe.compareAndSwapLong(array, offset, expect, update);
157			}
158
159			/**
160			* Atomically sets the element at position {@code i} to the given
161			* updated value
162			* if the current value is <a href="#bitEquals">bitwise equal</a>
163			* to the expected value.
164			*
165			* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
166			* and does not provide ordering guarantees, so is only rarely an
167			* appropriate alternative to {@code compareAndSet}.
168			*
169			* @param i the index
170			* @param expect the expected value
171			* @param update the new value
172			* @return true if successful
173			*/
174			public final boolean weakCompareAndSet(int i, double expect, double update) {
175			return compareAndSet(i, expect, update);
176			}
177
178			/**
179			* Atomically adds the given value to the element at index {@code i}.
180			*
181			* @param i the index
182			* @param delta the value to add
183			* @return the previous value
184			*/
185			public final double getAndAdd(int i, double delta) {
186			long offset = checkedByteOffset(i);
187			while (true) {
188			long current = getRaw(offset);
189			double currentVal = longBitsToDouble(current);
190			double nextVal = currentVal + delta;
191			long next = doubleToRawLongBits(nextVal);
192			if (compareAndSetRaw(offset, current, next))
193			return currentVal;
194			}
195			}
196
197			/**
198			* Atomically adds the given value to the element at index {@code i}.
199			*
200			* @param i the index
201			* @param delta the value to add
202			* @return the updated value
203			*/
204			public double addAndGet(int i, double delta) {
205			long offset = checkedByteOffset(i);
206			while (true) {
207			long current = getRaw(offset);
208			double currentVal = longBitsToDouble(current);
209			double nextVal = currentVal + delta;
210			long next = doubleToRawLongBits(nextVal);
211			if (compareAndSetRaw(offset, current, next))
212			return nextVal;
213			}
214			}
215
216			/**
217			* Returns the String representation of the current values of array.
218			* @return the String representation of the current values of array
219			*/
220			public String toString() {
221			int iMax = array.length - 1;
222			if (iMax == -1)
223			return "[]";
224
225			StringBuilder b = new StringBuilder();
226			b.append('[');
227			for (int i = 0; ; i++) {
228			b.append(longBitsToDouble(getRaw(byteOffset(i))));
229			if (i == iMax)
230			return b.append(']').toString();
231			b.append(',').append(' ');
232			}
233			}
234
235			// Unsafe mechanics
236			private static final sun.misc.Unsafe unsafe = getUnsafe();
237			private static final int base = unsafe.arrayBaseOffset(long[].class);
238			private static final int shift;
239
240			static {
241			int scale = unsafe.arrayIndexScale(long[].class);
242			if ((scale & (scale - 1)) != 0)
243			throw new Error("data type scale not a power of two");
244			shift = 31 - Integer.numberOfLeadingZeros(scale);
245			}
246
247			/**
248			* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
249			* Replace with a simple call to Unsafe.getUnsafe when integrating
250			* into a jdk.
251			*
252			* @return a sun.misc.Unsafe
253			*/
254			private static sun.misc.Unsafe getUnsafe() {
255			try {
256			return sun.misc.Unsafe.getUnsafe();
257			} catch (SecurityException se) {
258			try {
259			return java.security.AccessController.doPrivileged
260			(new java.security
261			.PrivilegedExceptionAction<sun.misc.Unsafe>() {
262			public sun.misc.Unsafe run() throws Exception {
263			java.lang.reflect.Field f = sun.misc
264			.Unsafe.class.getDeclaredField("theUnsafe");
265			f.setAccessible(true);
266			return (sun.misc.Unsafe) f.get(null);
267			}});
268			} catch (java.security.PrivilegedActionException e) {
269			throw new RuntimeException("Could not initialize intrinsics",
270			e.getCause());
271			}
272			}
273			}
274			}