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
 * 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 {
    static final long serialVersionUID = -8405198993435143622L;

    private 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() { this(0.0); }

    /**
     * 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="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();
    }

    // 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 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:	1.7
Committed:	Wed Oct 19 23:01:30 2011 UTC (12 years, 7 months ago) by jsr166
Branch:	MAIN
Changes since 1.6:	+3 -0 lines
Log Message:	add @see to scalable updaters
#	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			* boolean bitEquals(double x, double y) {
29			* 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	1.3	static final long serialVersionUID = -8405198993435143622L;
42	jsr166	1.1
43			private volatile long value;
44
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			public AtomicDouble() { this(0.0); }
58
59			/**
60			* Gets the current value.
61			*
62			* @return the current value
63			*/
64			public final double get() {
65			return longBitsToDouble(value);
66			}
67
68			/**
69			* Sets to the given value.
70			*
71			* @param newValue the new value
72			*/
73			public final void set(double newValue) {
74	jsr166	1.5	long next = doubleToRawLongBits(newValue);
75			value = next;
76	jsr166	1.1	}
77
78			/**
79			* Eventually sets to the given value.
80			*
81			* @param newValue the new value
82			*/
83			public final void lazySet(double newValue) {
84	jsr166	1.5	long next = doubleToRawLongBits(newValue);
85			unsafe.putOrderedLong(this, valueOffset, next);
86	jsr166	1.1	}
87
88			/**
89			* Atomically sets to the given value and returns the old value.
90			*
91			* @param newValue the new value
92			* @return the previous value
93			*/
94			public final double getAndSet(double newValue) {
95	jsr166	1.5	long next = doubleToRawLongBits(newValue);
96	jsr166	1.1	while (true) {
97	jsr166	1.5	long current = value;
98			if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
99			return longBitsToDouble(current);
100	jsr166	1.1	}
101			}
102
103			/**
104			* Atomically sets the value to the given updated value
105	jsr166	1.5	* if the current value is <a href="#bitEquals">bitwise equal</a>
106			* to the expected value.
107	jsr166	1.1	*
108			* @param expect the expected value
109			* @param update the new value
110	jsr166	1.5	* @return {@code true} if successful. False return indicates that
111			* the actual value was not bitwise equal to the expected value.
112	jsr166	1.1	*/
113			public final boolean compareAndSet(double expect, double update) {
114			return unsafe.compareAndSwapLong(this, valueOffset,
115			doubleToRawLongBits(expect),
116			doubleToRawLongBits(update));
117			}
118
119			/**
120			* Atomically sets the value to the given updated value
121	jsr166	1.5	* if the current value is <a href="#bitEquals">bitwise equal</a>
122			* to the expected value.
123	jsr166	1.1	*
124			* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
125			* and does not provide ordering guarantees, so is only rarely an
126			* appropriate alternative to {@code compareAndSet}.
127			*
128			* @param expect the expected value
129			* @param update the new value
130	jsr166	1.5	* @return {@code true} if successful
131	jsr166	1.1	*/
132			public final boolean weakCompareAndSet(double expect, double update) {
133			return compareAndSet(expect, update);
134			}
135
136			/**
137			* Atomically adds the given value to the current value.
138			*
139			* @param delta the value to add
140			* @return the previous value
141			*/
142			public final double getAndAdd(double delta) {
143			while (true) {
144	jsr166	1.5	long current = value;
145			double currentVal = longBitsToDouble(current);
146			double nextVal = currentVal + delta;
147			long next = doubleToRawLongBits(nextVal);
148			if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
149			return currentVal;
150	jsr166	1.1	}
151			}
152
153			/**
154			* Atomically adds the given value to the current value.
155			*
156			* @param delta the value to add
157			* @return the updated value
158			*/
159			public final double addAndGet(double delta) {
160	jsr166	1.5	while (true) {
161			long current = value;
162			double currentVal = longBitsToDouble(current);
163			double nextVal = currentVal + delta;
164			long next = doubleToRawLongBits(nextVal);
165			if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
166			return nextVal;
167	jsr166	1.1	}
168			}
169
170			/**
171			* Returns the String representation of the current value.
172	jsr166	1.5	* @return the String representation of the current value
173	jsr166	1.1	*/
174			public String toString() {
175			return Double.toString(get());
176			}
177
178			/**
179			* Returns the value of this {@code AtomicDouble} as an {@code int}
180			* after a narrowing primitive conversion.
181			*/
182			public int intValue() {
183			return (int)get();
184			}
185
186			/**
187	jsr166	1.5	* Returns the value of this {@code AtomicDouble} as a {@code long}
188			* after a narrowing primitive conversion.
189	jsr166	1.1	*/
190			public long longValue() {
191			return (long)get();
192			}
193
194			/**
195			* Returns the value of this {@code AtomicDouble} as a {@code float}
196	jsr166	1.5	* after a narrowing primitive conversion.
197	jsr166	1.1	*/
198			public float floatValue() {
199			return (float)get();
200			}
201
202			/**
203	jsr166	1.5	* Returns the value of this {@code AtomicDouble} as a {@code double}.
204	jsr166	1.1	*/
205			public double doubleValue() {
206			return get();
207			}
208
209	jsr166	1.5	// Unsafe mechanics
210			private static final sun.misc.Unsafe unsafe = getUnsafe();
211			private static final long valueOffset;
212
213			static {
214			try {
215			valueOffset = unsafe.objectFieldOffset
216			(AtomicDouble.class.getDeclaredField("value"));
217			} catch (Exception ex) { throw new Error(ex); }
218			}
219
220	jsr166	1.3	/**
221			* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
222			* Replace with a simple call to Unsafe.getUnsafe when integrating
223			* into a jdk.
224			*
225			* @return a sun.misc.Unsafe
226			*/
227			private static sun.misc.Unsafe getUnsafe() {
228			try {
229			return sun.misc.Unsafe.getUnsafe();
230			} catch (SecurityException se) {
231			try {
232			return java.security.AccessController.doPrivileged
233			(new java.security
234			.PrivilegedExceptionAction<sun.misc.Unsafe>() {
235			public sun.misc.Unsafe run() throws Exception {
236			java.lang.reflect.Field f = sun.misc
237			.Unsafe.class.getDeclaredField("theUnsafe");
238			f.setAccessible(true);
239			return (sun.misc.Unsafe) f.get(null);
240			}});
241			} catch (java.security.PrivilegedActionException e) {
242			throw new RuntimeException("Could not initialize intrinsics",
243			e.getCause());
244			}
245			}
246			}
247	jsr166	1.1	}