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
#	Content
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	}