jsr166e/extra/AtomicDouble.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;
import sun.misc.Unsafe;

/**
 * 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 atomically
 * incremented sequence numbers, and cannot be used as a replacement
 * for a {@link java.lang.Double}. However, this class does extend
 * {@code Number} to allow uniform access by tools and utilities that
 * deal with numerically-based classes.
 *
 * @since 1.5
 * @author Doug Lea
 */
public class AtomicDouble extends Number implements java.io.Serializable {
    private static final long serialVersionUID = 1927816293512124184L;

    // setup to use Unsafe.compareAndSwapLong for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;

    /**
     * Records whether the underlying JVM supports lockless
     * compareAndSwap for longs. While the Unsafe.compareAndSwapLong
     * method works in either case, some constructions should be
     * handled at Java level to avoid locking user-visible locks.
     */
    static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();

    /**
     * Returns whether underlying JVM supports lockless CompareAndSet
     * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
     */
    private static native boolean VMSupportsCS8();

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

    private volatile long value;

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

    /**
     * Creates a new 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) {
        value = doubleToRawLongBits(newValue);
    }

    /**
     * Eventually sets to the given value.
     *
     * @param newValue the new value
     * @since 1.6
     */
    public final void lazySet(double newValue) {
        unsafe.putOrderedLong(this, valueOffset, doubleToRawLongBits(newValue));
    }

    /**
     * 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 newBits = doubleToRawLongBits(newValue);
        while (true) {
            long currentBits = value;
            if (compareAndSet(currentBits, newBits))
                return longBitsToDouble(currentBits);
        }
    }

    /**
     * Atomically sets the value to the given updated value
     * if the current value {@code ==} the expected value.
     *
     * @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(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 {@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 expect the expected value
     * @param update the new value
     * @return 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 currentBits = value;
            long nextBits = doubleToRawLongBits(longBitsToDouble(currentBits) + delta);
            if (compareAndSet(currentBits, nextBits))
                return longBitsToDouble(currentBits);
        }
    }

    /**
     * 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) {
        for (;;) {
            double current = get();
            double next = current + delta;
            if (compareAndSet(current, next))
                return next;
        }
    }

    /**
     * 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}.
     */
    public long longValue() {
        return (long)get();
    }

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

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

}
Revision:	1.1
Committed:	Tue Aug 9 04:05:25 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			import static java.lang.Double.doubleToRawLongBits;
9			import static java.lang.Double.longBitsToDouble;
10			import sun.misc.Unsafe;
11
12			/**
13			* A {@code double} value that may be updated atomically. See the
14			* {@link java.util.concurrent.atomic} package specification for
15			* description of the properties of atomic variables. An
16			* {@code AtomicDouble} is used in applications such as atomically
17			* incremented sequence numbers, and cannot be used as a replacement
18			* for a {@link java.lang.Double}. However, this class does extend
19			* {@code Number} to allow uniform access by tools and utilities that
20			* deal with numerically-based classes.
21			*
22			* @since 1.5
23			* @author Doug Lea
24			*/
25			public class AtomicDouble extends Number implements java.io.Serializable {
26			private static final long serialVersionUID = 1927816293512124184L;
27
28			// setup to use Unsafe.compareAndSwapLong for updates
29			private static final Unsafe unsafe = Unsafe.getUnsafe();
30			private static final long valueOffset;
31
32			/**
33			* Records whether the underlying JVM supports lockless
34			* compareAndSwap for longs. While the Unsafe.compareAndSwapLong
35			* method works in either case, some constructions should be
36			* handled at Java level to avoid locking user-visible locks.
37			*/
38			static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();
39
40			/**
41			* Returns whether underlying JVM supports lockless CompareAndSet
42			* for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
43			*/
44			private static native boolean VMSupportsCS8();
45
46			static {
47			try {
48			valueOffset = unsafe.objectFieldOffset
49			(AtomicDouble.class.getDeclaredField("value"));
50			} catch (Exception ex) { throw new Error(ex); }
51			}
52
53			private volatile long value;
54
55			/**
56			* Creates a new AtomicDouble with the given initial value.
57			*
58			* @param initialValue the initial value
59			*/
60			public AtomicDouble(double initialValue) {
61			value = doubleToRawLongBits(initialValue);
62			}
63
64			/**
65			* Creates a new AtomicDouble with initial value {@code 0.0}.
66			*/
67			public AtomicDouble() { this(0.0); }
68
69			/**
70			* Gets the current value.
71			*
72			* @return the current value
73			*/
74			public final double get() {
75			return longBitsToDouble(value);
76			}
77
78			/**
79			* Sets to the given value.
80			*
81			* @param newValue the new value
82			*/
83			public final void set(double newValue) {
84			value = doubleToRawLongBits(newValue);
85			}
86
87			/**
88			* Eventually sets to the given value.
89			*
90			* @param newValue the new value
91			* @since 1.6
92			*/
93			public final void lazySet(double newValue) {
94			unsafe.putOrderedLong(this, valueOffset, doubleToRawLongBits(newValue));
95			}
96
97			/**
98			* Atomically sets to the given value and returns the old value.
99			*
100			* @param newValue the new value
101			* @return the previous value
102			*/
103			public final double getAndSet(double newValue) {
104			long newBits = doubleToRawLongBits(newValue);
105			while (true) {
106			long currentBits = value;
107			if (compareAndSet(currentBits, newBits))
108			return longBitsToDouble(currentBits);
109			}
110			}
111
112			/**
113			* Atomically sets the value to the given updated value
114			* if the current value {@code ==} the expected value.
115			*
116			* @param expect the expected value
117			* @param update the new value
118			* @return true if successful. False return indicates that
119			* the actual value was not equal to the expected value.
120			*/
121			public final boolean compareAndSet(double expect, double update) {
122			return unsafe.compareAndSwapLong(this, valueOffset,
123			doubleToRawLongBits(expect),
124			doubleToRawLongBits(update));
125			}
126
127			/**
128			* Atomically sets the value to the given updated value
129			* if the current value {@code ==} the expected value.
130			*
131			* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
132			* and does not provide ordering guarantees, so is only rarely an
133			* appropriate alternative to {@code compareAndSet}.
134			*
135			* @param expect the expected value
136			* @param update the new value
137			* @return true if successful.
138			*/
139			public final boolean weakCompareAndSet(double expect, double update) {
140			return compareAndSet(expect, update);
141			}
142
143			/**
144			* Atomically adds the given value to the current value.
145			*
146			* @param delta the value to add
147			* @return the previous value
148			*/
149			public final double getAndAdd(double delta) {
150			while (true) {
151			long currentBits = value;
152			long nextBits = doubleToRawLongBits(longBitsToDouble(currentBits) + delta);
153			if (compareAndSet(currentBits, nextBits))
154			return longBitsToDouble(currentBits);
155			}
156			}
157
158			/**
159			* Atomically adds the given value to the current value.
160			*
161			* @param delta the value to add
162			* @return the updated value
163			*/
164			public final double addAndGet(double delta) {
165			for (;;) {
166			double current = get();
167			double next = current + delta;
168			if (compareAndSet(current, next))
169			return next;
170			}
171			}
172
173			/**
174			* Returns the String representation of the current value.
175			* @return the String representation of the current value.
176			*/
177			public String toString() {
178			return Double.toString(get());
179			}
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			return (int)get();
188			}
189
190			/**
191			* Returns the value of this {@code AtomicDouble} as a {@code long}.
192			*/
193			public long longValue() {
194			return (long)get();
195			}
196
197			/**
198			* Returns the value of this {@code AtomicDouble} as a {@code float}
199			* after a widening primitive conversion.
200			*/
201			public float floatValue() {
202			return (float)get();
203			}
204
205			/**
206			* Returns the value of this {@code AtomicDouble} as a {@code double}
207			* after a widening primitive conversion.
208			*/
209			public double doubleValue() {
210			return get();
211			}
212
213			}