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 id="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
 * static 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 transient 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><a
     * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
     * 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 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 "[]";

        // Double.toString(Math.PI).length() == 17
        StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
        b.append('[');
        for (int i = 0;; i++) {
            b.append(longBitsToDouble(getRaw(byteOffset(i))));
            if (i == iMax)
                return b.append(']').toString();
            b.append(',').append(' ');
        }
    }

    /**
     * Saves the state to a stream (that is, serializes it).
     *
     * @param s the stream
     * @throws java.io.IOException if an I/O error occurs
     * @serialData The length of the array is emitted (int), followed by all
     *             of its elements (each a {@code double}) in the proper order.
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();

        // Write out array length
        int length = length();
        s.writeInt(length);

        // Write out all elements in the proper order.
        for (int i = 0; i < length; i++)
            s.writeDouble(get(i));
    }

    /**
     * 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 {
        s.defaultReadObject();

        // Read in array length and allocate array
        int length = s.readInt();
        unsafe.putObjectVolatile(this, arrayOffset, new long[length]);

        // Read in all elements in the proper order.
        for (int i = 0; i < length; i++)
            set(i, s.readDouble());
    }

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

    static {
        try {
            Class<?> k = AtomicDoubleArray.class;
            arrayOffset = unsafe.objectFieldOffset
                (k.getDeclaredField("array"));
            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);
        } catch (Exception e) {
            throw new Error(e);
        }
    }

    /**
     * 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 tryReflectionInstead) {}
        try {
            return java.security.AccessController.doPrivileged
            (new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
                public sun.misc.Unsafe run() throws Exception {
                    Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
                    for (java.lang.reflect.Field f : k.getDeclaredFields()) {
                        f.setAccessible(true);
                        Object x = f.get(null);
                        if (k.isInstance(x))
                            return k.cast(x);
                    }
                    throw new NoSuchFieldError("the Unsafe");
                }});
        } catch (java.security.PrivilegedActionException e) {
            throw new RuntimeException("Could not initialize intrinsics",
                                       e.getCause());
        }
    }
}
Revision:	1.11
Committed:	Mon Jul 22 16:47:46 2013 UTC (10 years, 10 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.10:	+6 -0 lines
Log Message:	fix javadoc warnings for serialization methods
#	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	jsr166	1.8	* <p id="bitEquals">This class compares primitive {@code double}
18	jsr166	1.1	* 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	jsr166	1.3	* static boolean bitEquals(double x, double y) {
24	jsr166	1.1	* long xBits = Double.doubleToRawLongBits(x);
25			* long yBits = Double.doubleToRawLongBits(y);
26			* return xBits == yBits;
27	jsr166	1.8	* }}</pre>
28	jsr166	1.1	*
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	jsr166	1.4	private final transient long[] array;
36	jsr166	1.1
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	jsr166	1.9	* <p><a
166	jsr166	1.2	* href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
167	jsr166	1.9	* May fail spuriously and does not provide ordering guarantees</a>,
168			* so is only rarely an appropriate alternative to {@code compareAndSet}.
169	jsr166	1.1	*
170			* @param i the index
171			* @param expect the expected value
172			* @param update the new value
173			* @return true if successful
174			*/
175			public final boolean weakCompareAndSet(int i, double expect, double update) {
176			return compareAndSet(i, expect, update);
177			}
178
179			/**
180			* Atomically adds the given value to the element at index {@code i}.
181			*
182			* @param i the index
183			* @param delta the value to add
184			* @return the previous value
185			*/
186			public final double getAndAdd(int i, double delta) {
187			long offset = checkedByteOffset(i);
188			while (true) {
189			long current = getRaw(offset);
190			double currentVal = longBitsToDouble(current);
191			double nextVal = currentVal + delta;
192			long next = doubleToRawLongBits(nextVal);
193			if (compareAndSetRaw(offset, current, next))
194			return currentVal;
195			}
196			}
197
198			/**
199			* Atomically adds the given value to the element at index {@code i}.
200			*
201			* @param i the index
202			* @param delta the value to add
203			* @return the updated value
204			*/
205			public double addAndGet(int i, double delta) {
206			long offset = checkedByteOffset(i);
207			while (true) {
208			long current = getRaw(offset);
209			double currentVal = longBitsToDouble(current);
210			double nextVal = currentVal + delta;
211			long next = doubleToRawLongBits(nextVal);
212			if (compareAndSetRaw(offset, current, next))
213			return nextVal;
214			}
215			}
216
217			/**
218			* Returns the String representation of the current values of array.
219			* @return the String representation of the current values of array
220			*/
221			public String toString() {
222			int iMax = array.length - 1;
223			if (iMax == -1)
224			return "[]";
225
226	jsr166	1.2	// Double.toString(Math.PI).length() == 17
227			StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
228	jsr166	1.1	b.append('[');
229	jsr166	1.2	for (int i = 0;; i++) {
230	jsr166	1.1	b.append(longBitsToDouble(getRaw(byteOffset(i))));
231			if (i == iMax)
232			return b.append(']').toString();
233			b.append(',').append(' ');
234			}
235			}
236
237	jsr166	1.4	/**
238			* Saves the state to a stream (that is, serializes it).
239			*
240	jsr166	1.11	* @param s the stream
241			* @throws java.io.IOException if an I/O error occurs
242	jsr166	1.4	* @serialData The length of the array is emitted (int), followed by all
243			* of its elements (each a {@code double}) in the proper order.
244			*/
245			private void writeObject(java.io.ObjectOutputStream s)
246	jsr166	1.5	throws java.io.IOException {
247	jsr166	1.4	s.defaultWriteObject();
248
249			// Write out array length
250			int length = length();
251			s.writeInt(length);
252
253			// Write out all elements in the proper order.
254			for (int i = 0; i < length; i++)
255			s.writeDouble(get(i));
256			}
257
258			/**
259			* Reconstitutes the instance from a stream (that is, deserializes it).
260	jsr166	1.11	* @param s the stream
261			* @throws ClassNotFoundException if the class of a serialized object
262			* could not be found
263			* @throws java.io.IOException if an I/O error occurs
264	jsr166	1.4	*/
265			private void readObject(java.io.ObjectInputStream s)
266			throws java.io.IOException, ClassNotFoundException {
267			s.defaultReadObject();
268
269			// Read in array length and allocate array
270			int length = s.readInt();
271			unsafe.putObjectVolatile(this, arrayOffset, new long[length]);
272
273			// Read in all elements in the proper order.
274			for (int i = 0; i < length; i++)
275			set(i, s.readDouble());
276			}
277
278	jsr166	1.1	// Unsafe mechanics
279			private static final sun.misc.Unsafe unsafe = getUnsafe();
280	jsr166	1.4	private static final long arrayOffset;
281	jsr166	1.1	private static final int base = unsafe.arrayBaseOffset(long[].class);
282			private static final int shift;
283
284			static {
285	jsr166	1.4	try {
286			Class<?> k = AtomicDoubleArray.class;
287			arrayOffset = unsafe.objectFieldOffset
288			(k.getDeclaredField("array"));
289			int scale = unsafe.arrayIndexScale(long[].class);
290			if ((scale & (scale - 1)) != 0)
291			throw new Error("data type scale not a power of two");
292			shift = 31 - Integer.numberOfLeadingZeros(scale);
293			} catch (Exception e) {
294			throw new Error(e);
295			}
296	jsr166	1.1	}
297
298			/**
299			* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
300			* Replace with a simple call to Unsafe.getUnsafe when integrating
301			* into a jdk.
302			*
303			* @return a sun.misc.Unsafe
304			*/
305			private static sun.misc.Unsafe getUnsafe() {
306			try {
307			return sun.misc.Unsafe.getUnsafe();
308	jsr166	1.6	} catch (SecurityException tryReflectionInstead) {}
309			try {
310			return java.security.AccessController.doPrivileged
311			(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
312			public sun.misc.Unsafe run() throws Exception {
313			Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
314			for (java.lang.reflect.Field f : k.getDeclaredFields()) {
315			f.setAccessible(true);
316			Object x = f.get(null);
317			if (k.isInstance(x))
318			return k.cast(x);
319			}
320			throw new NoSuchFieldError("the Unsafe");
321			}});
322			} catch (java.security.PrivilegedActionException e) {
323			throw new RuntimeException("Could not initialize intrinsics",
324			e.getCause());
325	jsr166	1.1	}
326			}
327			}