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
#	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
10	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	* description of the properties of atomic variables. An {@code
17	* AtomicDouble} is used in applications such as atomic accumulation,
18	* and 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><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	* <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	*
34	* @see jsr166e.DoubleAdder
35	* @see jsr166e.DoubleMaxUpdater
36	*
37	* @author Doug Lea
38	* @author Martin Buchholz
39	*/
40	public class AtomicDouble extends Number implements java.io.Serializable {
41	static final long serialVersionUID = -8405198993435143622L;
42
43	private volatile long value;
44
45	/**
46	* Creates a new {@code AtomicDouble} with the given initial value.
47	*
48	* @param initialValue the initial value
49	*/
50	public AtomicDouble(double initialValue) {
51	value = doubleToRawLongBits(initialValue);
52	}
53
54	/**
55	* Creates a new {@code AtomicDouble} with initial value {@code 0.0}.
56	*/
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	long next = doubleToRawLongBits(newValue);
75	value = next;
76	}
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	long next = doubleToRawLongBits(newValue);
85	unsafe.putOrderedLong(this, valueOffset, next);
86	}
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	long next = doubleToRawLongBits(newValue);
96	while (true) {
97	long current = value;
98	if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
99	return longBitsToDouble(current);
100	}
101	}
102
103	/**
104	* Atomically sets the value to the given updated value
105	* if the current value is <a href="#bitEquals">bitwise equal</a>
106	* to the expected value.
107	*
108	* @param expect the expected value
109	* @param update the new value
110	* @return {@code true} if successful. False return indicates that
111	* the actual value was not bitwise equal to the expected value.
112	*/
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	* if the current value is <a href="#bitEquals">bitwise equal</a>
122	* to the expected value.
123	*
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	* @return {@code true} if successful
131	*/
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	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	}
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	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	}
168	}
169
170	/**
171	* Returns the String representation of the current value.
172	* @return the String representation of the current value
173	*/
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	* Returns the value of this {@code AtomicDouble} as a {@code long}
188	* after a narrowing primitive conversion.
189	*/
190	public long longValue() {
191	return (long)get();
192	}
193
194	/**
195	* Returns the value of this {@code AtomicDouble} as a {@code float}
196	* after a narrowing primitive conversion.
197	*/
198	public float floatValue() {
199	return (float)get();
200	}
201
202	/**
203	* Returns the value of this {@code AtomicDouble} as a {@code double}.
204	*/
205	public double doubleValue() {
206	return get();
207	}
208
209	// 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	/**
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	}