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;
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 atomic summation, 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>This class differs from the primitive double {@code ==} operator
 * and from {@link Double#equals} in that it uses purely bitwise
 * equality in methods such as {@link #compareAndSet}, 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>
 * 
 * @since 1.5
 * @author Doug Lea
 * @author Martin Buchholz
 */
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 boolean VMSupportsCS8() {
        try {
            Class<?> klazz = java.util.concurrent.atomic.AtomicLong.class;
            java.lang.reflect.Method m =
                klazz.getDeclaredMethod("VMSupportsCS8", new Class<?>[0]);
            m.setAccessible(true);
            return (Boolean) m.invoke(new Class<?>[0]);
        } catch (Throwable t) { throw new Error(t); }
    }

    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 (unsafe.compareAndSwapLong(this, valueOffset,
                                          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 (unsafe.compareAndSwapLong(this, valueOffset,
                                          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:	1.2
Committed:	Tue Aug 9 07:44:08 2011 UTC (12 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.1:	+33 -11 lines
Log Message:	mostly works
#	Content
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	* http://creativecommons.org/publicdomain/zero/1.0/
6	*/
7
8	package jsr166e.extra;
9	import static java.lang.Double.doubleToRawLongBits;
10	import static java.lang.Double.longBitsToDouble;
11	import sun.misc.Unsafe;
12
13	/**
14	* A {@code double} value that may be updated atomically. See the
15	* {@link java.util.concurrent.atomic} package specification for
16	* description of the properties of atomic variables. An {@code
17	* AtomicDouble} is used in applications such as atomic summation, and
18	* cannot be used as a replacement for a {@link Double}. However,
19	* this class does extend {@code Number} to allow uniform access by
20	* tools and utilities that deal with numerically-based classes.
21	*
22	* <p>This class differs from the primitive double {@code ==} operator
23	* and from {@link Double#equals} in that it uses purely bitwise
24	* equality in methods such as {@link #compareAndSet}, as if
25	* implemented by:
26	* <pre> {@code
27	* boolean bitEquals(double x, double y) {
28	* long xBits = Double.doubleToRawLongBits(x);
29	* long yBits = Double.doubleToRawLongBits(y);
30	* return xBits == yBits;
31	* }}</pre>
32	*
33	* @since 1.5
34	* @author Doug Lea
35	* @author Martin Buchholz
36	*/
37	public class AtomicDouble extends Number implements java.io.Serializable {
38	private static final long serialVersionUID = 1927816293512124184L;
39
40	// setup to use Unsafe.compareAndSwapLong for updates
41	private static final Unsafe unsafe = Unsafe.getUnsafe();
42	private static final long valueOffset;
43
44	/**
45	* Records whether the underlying JVM supports lockless
46	* compareAndSwap for longs. While the Unsafe.compareAndSwapLong
47	* method works in either case, some constructions should be
48	* handled at Java level to avoid locking user-visible locks.
49	*/
50	static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();
51
52	/**
53	* Returns whether underlying JVM supports lockless CompareAndSet
54	* for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
55	*/
56	private static boolean VMSupportsCS8() {
57	try {
58	Class<?> klazz = java.util.concurrent.atomic.AtomicLong.class;
59	java.lang.reflect.Method m =
60	klazz.getDeclaredMethod("VMSupportsCS8", new Class<?>[0]);
61	m.setAccessible(true);
62	return (Boolean) m.invoke(new Class<?>[0]);
63	} catch (Throwable t) { throw new Error(t); }
64	}
65
66	static {
67	try {
68	valueOffset = unsafe.objectFieldOffset
69	(AtomicDouble.class.getDeclaredField("value"));
70	} catch (Exception ex) { throw new Error(ex); }
71	}
72
73	private volatile long value;
74
75	/**
76	* Creates a new AtomicDouble with the given initial value.
77	*
78	* @param initialValue the initial value
79	*/
80	public AtomicDouble(double initialValue) {
81	value = doubleToRawLongBits(initialValue);
82	}
83
84	/**
85	* Creates a new AtomicDouble with initial value {@code 0.0}.
86	*/
87	public AtomicDouble() { this(0.0); }
88
89	/**
90	* Gets the current value.
91	*
92	* @return the current value
93	*/
94	public final double get() {
95	return longBitsToDouble(value);
96	}
97
98	/**
99	* Sets to the given value.
100	*
101	* @param newValue the new value
102	*/
103	public final void set(double newValue) {
104	value = doubleToRawLongBits(newValue);
105	}
106
107	/**
108	* Eventually sets to the given value.
109	*
110	* @param newValue the new value
111	* @since 1.6
112	*/
113	public final void lazySet(double newValue) {
114	unsafe.putOrderedLong(this, valueOffset, doubleToRawLongBits(newValue));
115	}
116
117	/**
118	* Atomically sets to the given value and returns the old value.
119	*
120	* @param newValue the new value
121	* @return the previous value
122	*/
123	public final double getAndSet(double newValue) {
124	long newBits = doubleToRawLongBits(newValue);
125	while (true) {
126	long currentBits = value;
127	if (unsafe.compareAndSwapLong(this, valueOffset,
128	currentBits, newBits))
129	return longBitsToDouble(currentBits);
130	}
131	}
132
133	/**
134	* Atomically sets the value to the given updated value
135	* if the current value {@code ==} the expected value.
136	*
137	* @param expect the expected value
138	* @param update the new value
139	* @return true if successful. False return indicates that
140	* the actual value was not equal to the expected value.
141	*/
142	public final boolean compareAndSet(double expect, double update) {
143	return unsafe.compareAndSwapLong(this, valueOffset,
144	doubleToRawLongBits(expect),
145	doubleToRawLongBits(update));
146	}
147
148	/**
149	* Atomically sets the value to the given updated value
150	* if the current value {@code ==} the expected value.
151	*
152	* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
153	* and does not provide ordering guarantees, so is only rarely an
154	* appropriate alternative to {@code compareAndSet}.
155	*
156	* @param expect the expected value
157	* @param update the new value
158	* @return true if successful.
159	*/
160	public final boolean weakCompareAndSet(double expect, double update) {
161	return compareAndSet(expect, update);
162	}
163
164	/**
165	* Atomically adds the given value to the current value.
166	*
167	* @param delta the value to add
168	* @return the previous value
169	*/
170	public final double getAndAdd(double delta) {
171	while (true) {
172	long currentBits = value;
173	long nextBits = doubleToRawLongBits(longBitsToDouble(currentBits) + delta);
174	if (unsafe.compareAndSwapLong(this, valueOffset,
175	currentBits, nextBits))
176	return longBitsToDouble(currentBits);
177	}
178	}
179
180	/**
181	* Atomically adds the given value to the current value.
182	*
183	* @param delta the value to add
184	* @return the updated value
185	*/
186	public final double addAndGet(double delta) {
187	for (;;) {
188	double current = get();
189	double next = current + delta;
190	if (compareAndSet(current, next))
191	return next;
192	}
193	}
194
195	/**
196	* Returns the String representation of the current value.
197	* @return the String representation of the current value.
198	*/
199	public String toString() {
200	return Double.toString(get());
201	}
202
203
204	/**
205	* Returns the value of this {@code AtomicDouble} as an {@code int}
206	* after a narrowing primitive conversion.
207	*/
208	public int intValue() {
209	return (int)get();
210	}
211
212	/**
213	* Returns the value of this {@code AtomicDouble} as a {@code long}.
214	*/
215	public long longValue() {
216	return (long)get();
217	}
218
219	/**
220	* Returns the value of this {@code AtomicDouble} as a {@code float}
221	* after a widening primitive conversion.
222	*/
223	public float floatValue() {
224	return (float)get();
225	}
226
227	/**
228	* Returns the value of this {@code AtomicDouble} as a {@code double}
229	* after a widening primitive conversion.
230	*/
231	public double doubleValue() {
232	return get();
233	}
234
235	}