jsr166e/extra/AtomicDouble.java

/*
 * Written by Doug Lea and Martin Buchholz 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} value that may be updated atomically.  See the
 * {@link java.util.concurrent.atomic} package specification for
 * description of the properties of atomic variables.  An {@code
 * AtomicDouble} is used in applications such as atomic accumulation,
 * and cannot be used as a replacement for a {@link Double}.  However,
 * this class does extend {@code Number} to allow uniform access by
 * tools and utilities that deal with numerically-based classes.
 *
 * <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
 * static boolean bitEquals(double x, double y) {
 *   long xBits = Double.doubleToRawLongBits(x);
 *   long yBits = Double.doubleToRawLongBits(y);
 *   return xBits == yBits;
 * }}</pre>
 *
 * @see jsr166e.DoubleAdder
 * @see jsr166e.DoubleMaxUpdater
 *
 * @author Doug Lea
 * @author Martin Buchholz
 */
public class AtomicDouble extends Number implements java.io.Serializable {
    private static final long serialVersionUID = -8405198993435143622L;

    private transient volatile long value;

    /**
     * Creates a new {@code AtomicDouble} with the given initial value.
     *
     * @param initialValue the initial value
     */
    public AtomicDouble(double initialValue) {
        value = doubleToRawLongBits(initialValue);
    }

    /**
     * Creates a new {@code AtomicDouble} with initial value {@code 0.0}.
     */
    public AtomicDouble() {
        // assert doubleToRawLongBits(0.0) == 0L;
    }

    /**
     * Gets the current value.
     *
     * @return the current value
     */
    public final double get() {
        return longBitsToDouble(value);
    }

    /**
     * Sets to the given value.
     *
     * @param newValue the new value
     */
    public final void set(double newValue) {
        long next = doubleToRawLongBits(newValue);
        value = next;
    }

    /**
     * Eventually sets to the given value.
     *
     * @param newValue the new value
     */
    public final void lazySet(double newValue) {
        long next = doubleToRawLongBits(newValue);
        unsafe.putOrderedLong(this, valueOffset, next);
    }

    /**
     * Atomically sets to the given value and returns the old value.
     *
     * @param newValue the new value
     * @return the previous value
     */
    public final double getAndSet(double newValue) {
        long next = doubleToRawLongBits(newValue);
        while (true) {
            long current = value;
            if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
                return longBitsToDouble(current);
        }
    }

    /**
     * Atomically sets the value to the given updated value
     * if the current value is <a href="#bitEquals">bitwise equal</a>
     * to the expected value.
     *
     * @param expect the expected value
     * @param update the new value
     * @return {@code true} if successful. False return indicates that
     * the actual value was not bitwise equal to the expected value.
     */
    public final boolean compareAndSet(double expect, double update) {
        return unsafe.compareAndSwapLong(this, valueOffset,
                                         doubleToRawLongBits(expect),
                                         doubleToRawLongBits(update));
    }

    /**
     * Atomically sets the value to the given updated value
     * if the current value is <a href="#bitEquals">bitwise equal</a>
     * to the expected value.
     *
     * <p>May <a
     * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
     * fail spuriously</a>
     * and does not provide ordering guarantees, so is only rarely an
     * appropriate alternative to {@code compareAndSet}.
     *
     * @param expect the expected value
     * @param update the new value
     * @return {@code true} if successful
     */
    public final boolean weakCompareAndSet(double expect, double update) {
        return compareAndSet(expect, update);
    }

    /**
     * Atomically adds the given value to the current value.
     *
     * @param delta the value to add
     * @return the previous value
     */
    public final double getAndAdd(double delta) {
        while (true) {
            long current = value;
            double currentVal = longBitsToDouble(current);
            double nextVal = currentVal + delta;
            long next = doubleToRawLongBits(nextVal);
            if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
                return currentVal;
        }
    }

    /**
     * Atomically adds the given value to the current value.
     *
     * @param delta the value to add
     * @return the updated value
     */
    public final double addAndGet(double delta) {
        while (true) {
            long current = value;
            double currentVal = longBitsToDouble(current);
            double nextVal = currentVal + delta;
            long next = doubleToRawLongBits(nextVal);
            if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
                return nextVal;
        }
    }

    /**
     * Returns the String representation of the current value.
     * @return the String representation of the current value
     */
    public String toString() {
        return Double.toString(get());
    }

    /**
     * Returns the value of this {@code AtomicDouble} as an {@code int}
     * after a narrowing primitive conversion.
     */
    public int intValue() {
        return (int) get();
    }

    /**
     * Returns the value of this {@code AtomicDouble} as a {@code long}
     * after a narrowing primitive conversion.
     */
    public long longValue() {
        return (long) get();
    }

    /**
     * Returns the value of this {@code AtomicDouble} as a {@code float}
     * after a narrowing primitive conversion.
     */
    public float floatValue() {
        return (float) get();
    }

    /**
     * Returns the value of this {@code AtomicDouble} as a {@code double}.
     */
    public double doubleValue() {
        return get();
    }

    /**
     * Saves the state to a stream (that is, serializes it).
     *
     * @serialData The current value is emitted (a {@code double}).
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();

        s.writeDouble(get());
    }

    /**
     * Reconstitutes the instance from a stream (that is, deserializes it).
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();

        set(s.readDouble());
    }

    // Unsafe mechanics
    private static final sun.misc.Unsafe unsafe = getUnsafe();
    private static final long valueOffset;

    static {
        try {
            valueOffset = unsafe.objectFieldOffset
                (AtomicDouble.class.getDeclaredField("value"));
        } catch (Exception ex) { throw new Error(ex); }
    }

    /**
     * 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:	1.14
Committed:	Wed Jan 9 02:51:37 2013 UTC (11 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.13:	+17 -15 lines
Log Message:	more portable getUnsafe()
#	User	Rev	Content
1	jsr166	1.1	/*
2	jsr166	1.2	* Written by Doug Lea and Martin Buchholz with assistance from
3			* members of JCP JSR-166 Expert Group and released to the public
4			* domain, as explained at
5	jsr166	1.1	* http://creativecommons.org/publicdomain/zero/1.0/
6			*/
7
8			package jsr166e.extra;
9	jsr166	1.5
10	jsr166	1.1	import static java.lang.Double.doubleToRawLongBits;
11			import static java.lang.Double.longBitsToDouble;
12
13			/**
14			* A {@code double} value that may be updated atomically. See the
15			* {@link java.util.concurrent.atomic} package specification for
16	jsr166	1.2	* description of the properties of atomic variables. An {@code
17	jsr166	1.3	* AtomicDouble} is used in applications such as atomic accumulation,
18			* and cannot be used as a replacement for a {@link Double}. However,
19	jsr166	1.2	* this class does extend {@code Number} to allow uniform access by
20			* tools and utilities that deal with numerically-based classes.
21	jsr166	1.1	*
22	jsr166	1.5	* <p><a name="bitEquals">This class compares primitive {@code double}
23			* values in methods such as {@link #compareAndSet} by comparing their
24			* bitwise representation using {@link Double#doubleToRawLongBits},
25			* which differs from both the primitive double {@code ==} operator
26			* and from {@link Double#equals}, as if implemented by:
27	jsr166	1.2	* <pre> {@code
28	jsr166	1.10	* static boolean bitEquals(double x, double y) {
29	jsr166	1.2	* long xBits = Double.doubleToRawLongBits(x);
30			* long yBits = Double.doubleToRawLongBits(y);
31			* return xBits == yBits;
32			* }}</pre>
33	jsr166	1.3	*
34	jsr166	1.7	* @see jsr166e.DoubleAdder
35			* @see jsr166e.DoubleMaxUpdater
36			*
37	jsr166	1.1	* @author Doug Lea
38	jsr166	1.2	* @author Martin Buchholz
39	jsr166	1.1	*/
40			public class AtomicDouble extends Number implements java.io.Serializable {
41	jsr166	1.8	private static final long serialVersionUID = -8405198993435143622L;
42	jsr166	1.1
43	jsr166	1.12	private transient volatile long value;
44	jsr166	1.1
45			/**
46	jsr166	1.6	* Creates a new {@code AtomicDouble} with the given initial value.
47	jsr166	1.1	*
48			* @param initialValue the initial value
49			*/
50			public AtomicDouble(double initialValue) {
51			value = doubleToRawLongBits(initialValue);
52			}
53
54			/**
55	jsr166	1.6	* Creates a new {@code AtomicDouble} with initial value {@code 0.0}.
56	jsr166	1.1	*/
57	jsr166	1.9	public AtomicDouble() {
58			// assert doubleToRawLongBits(0.0) == 0L;
59			}
60	jsr166	1.1
61			/**
62			* Gets the current value.
63			*
64			* @return the current value
65			*/
66			public final double get() {
67			return longBitsToDouble(value);
68			}
69
70			/**
71			* Sets to the given value.
72			*
73			* @param newValue the new value
74			*/
75			public final void set(double newValue) {
76	jsr166	1.5	long next = doubleToRawLongBits(newValue);
77			value = next;
78	jsr166	1.1	}
79
80			/**
81			* Eventually sets to the given value.
82			*
83			* @param newValue the new value
84			*/
85			public final void lazySet(double newValue) {
86	jsr166	1.5	long next = doubleToRawLongBits(newValue);
87			unsafe.putOrderedLong(this, valueOffset, next);
88	jsr166	1.1	}
89
90			/**
91			* Atomically sets to the given value and returns the old value.
92			*
93			* @param newValue the new value
94			* @return the previous value
95			*/
96			public final double getAndSet(double newValue) {
97	jsr166	1.5	long next = doubleToRawLongBits(newValue);
98	jsr166	1.1	while (true) {
99	jsr166	1.5	long current = value;
100			if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
101			return longBitsToDouble(current);
102	jsr166	1.1	}
103			}
104
105			/**
106			* Atomically sets the value to the given updated value
107	jsr166	1.5	* if the current value is <a href="#bitEquals">bitwise equal</a>
108			* to the expected value.
109	jsr166	1.1	*
110			* @param expect the expected value
111			* @param update the new value
112	jsr166	1.5	* @return {@code true} if successful. False return indicates that
113			* the actual value was not bitwise equal to the expected value.
114	jsr166	1.1	*/
115			public final boolean compareAndSet(double expect, double update) {
116			return unsafe.compareAndSwapLong(this, valueOffset,
117			doubleToRawLongBits(expect),
118			doubleToRawLongBits(update));
119			}
120
121			/**
122			* Atomically sets the value to the given updated value
123	jsr166	1.5	* if the current value is <a href="#bitEquals">bitwise equal</a>
124			* to the expected value.
125	jsr166	1.1	*
126	jsr166	1.9	* <p>May <a
127			* href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
128			* fail spuriously</a>
129	jsr166	1.1	* and does not provide ordering guarantees, so is only rarely an
130			* appropriate alternative to {@code compareAndSet}.
131			*
132			* @param expect the expected value
133			* @param update the new value
134	jsr166	1.5	* @return {@code true} if successful
135	jsr166	1.1	*/
136			public final boolean weakCompareAndSet(double expect, double update) {
137			return compareAndSet(expect, update);
138			}
139
140			/**
141			* Atomically adds the given value to the current value.
142			*
143			* @param delta the value to add
144			* @return the previous value
145			*/
146			public final double getAndAdd(double delta) {
147			while (true) {
148	jsr166	1.5	long current = value;
149			double currentVal = longBitsToDouble(current);
150			double nextVal = currentVal + delta;
151			long next = doubleToRawLongBits(nextVal);
152			if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
153			return currentVal;
154	jsr166	1.1	}
155			}
156
157			/**
158			* Atomically adds the given value to the current value.
159			*
160			* @param delta the value to add
161			* @return the updated value
162			*/
163			public final double addAndGet(double delta) {
164	jsr166	1.5	while (true) {
165			long current = value;
166			double currentVal = longBitsToDouble(current);
167			double nextVal = currentVal + delta;
168			long next = doubleToRawLongBits(nextVal);
169			if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
170			return nextVal;
171	jsr166	1.1	}
172			}
173
174			/**
175			* Returns the String representation of the current value.
176	jsr166	1.5	* @return the String representation of the current value
177	jsr166	1.1	*/
178			public String toString() {
179			return Double.toString(get());
180			}
181
182			/**
183			* Returns the value of this {@code AtomicDouble} as an {@code int}
184			* after a narrowing primitive conversion.
185			*/
186			public int intValue() {
187	jsr166	1.9	return (int) get();
188	jsr166	1.1	}
189
190			/**
191	jsr166	1.5	* Returns the value of this {@code AtomicDouble} as a {@code long}
192			* after a narrowing primitive conversion.
193	jsr166	1.1	*/
194			public long longValue() {
195	jsr166	1.9	return (long) get();
196	jsr166	1.1	}
197
198			/**
199			* Returns the value of this {@code AtomicDouble} as a {@code float}
200	jsr166	1.5	* after a narrowing primitive conversion.
201	jsr166	1.1	*/
202			public float floatValue() {
203	jsr166	1.9	return (float) get();
204	jsr166	1.1	}
205
206			/**
207	jsr166	1.5	* Returns the value of this {@code AtomicDouble} as a {@code double}.
208	jsr166	1.1	*/
209			public double doubleValue() {
210			return get();
211			}
212
213	jsr166	1.11	/**
214			* Saves the state to a stream (that is, serializes it).
215			*
216			* @serialData The current value is emitted (a {@code double}).
217			*/
218			private void writeObject(java.io.ObjectOutputStream s)
219	jsr166	1.13	throws java.io.IOException {
220	jsr166	1.11	s.defaultWriteObject();
221
222			s.writeDouble(get());
223			}
224
225			/**
226			* Reconstitutes the instance from a stream (that is, deserializes it).
227			*/
228			private void readObject(java.io.ObjectInputStream s)
229			throws java.io.IOException, ClassNotFoundException {
230			s.defaultReadObject();
231
232			set(s.readDouble());
233			}
234
235	jsr166	1.5	// Unsafe mechanics
236			private static final sun.misc.Unsafe unsafe = getUnsafe();
237			private static final long valueOffset;
238
239			static {
240			try {
241			valueOffset = unsafe.objectFieldOffset
242			(AtomicDouble.class.getDeclaredField("value"));
243			} catch (Exception ex) { throw new Error(ex); }
244			}
245
246	jsr166	1.3	/**
247			* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
248			* Replace with a simple call to Unsafe.getUnsafe when integrating
249			* into a jdk.
250			*
251			* @return a sun.misc.Unsafe
252			*/
253			private static sun.misc.Unsafe getUnsafe() {
254			try {
255			return sun.misc.Unsafe.getUnsafe();
256	jsr166	1.14	} catch (SecurityException tryReflectionInstead) {}
257			try {
258			return java.security.AccessController.doPrivileged
259			(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
260			public sun.misc.Unsafe run() throws Exception {
261			Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
262			for (java.lang.reflect.Field f : k.getDeclaredFields()) {
263			f.setAccessible(true);
264			Object x = f.get(null);
265			if (k.isInstance(x))
266			return k.cast(x);
267			}
268			throw new NoSuchFieldError("the Unsafe");
269			}});
270			} catch (java.security.PrivilegedActionException e) {
271			throw new RuntimeException("Could not initialize intrinsics",
272			e.getCause());
273	jsr166	1.3	}
274			}
275	jsr166	1.1	}