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>
 *
 * @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 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) {
        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:	1.5
Committed:	Wed Aug 10 01:29:45 2011 UTC (12 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.4:	+50 -43 lines
Log Message:	seems production ready
#	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	* @author Doug Lea
35	* @author Martin Buchholz
36	*/
37	public class AtomicDouble extends Number implements java.io.Serializable {
38	static final long serialVersionUID = -8405198993435143622L;
39
40	private volatile long value;
41
42	/**
43	* Creates a new AtomicDouble with the given initial value.
44	*
45	* @param initialValue the initial value
46	*/
47	public AtomicDouble(double initialValue) {
48	value = doubleToRawLongBits(initialValue);
49	}
50
51	/**
52	* Creates a new AtomicDouble with initial value {@code 0.0}.
53	*/
54	public AtomicDouble() { this(0.0); }
55
56	/**
57	* Gets the current value.
58	*
59	* @return the current value
60	*/
61	public final double get() {
62	return longBitsToDouble(value);
63	}
64
65	/**
66	* Sets to the given value.
67	*
68	* @param newValue the new value
69	*/
70	public final void set(double newValue) {
71	long next = doubleToRawLongBits(newValue);
72	value = next;
73	}
74
75	/**
76	* Eventually sets to the given value.
77	*
78	* @param newValue the new value
79	*/
80	public final void lazySet(double newValue) {
81	long next = doubleToRawLongBits(newValue);
82	unsafe.putOrderedLong(this, valueOffset, next);
83	}
84
85	/**
86	* Atomically sets to the given value and returns the old value.
87	*
88	* @param newValue the new value
89	* @return the previous value
90	*/
91	public final double getAndSet(double newValue) {
92	long next = doubleToRawLongBits(newValue);
93	while (true) {
94	long current = value;
95	if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
96	return longBitsToDouble(current);
97	}
98	}
99
100	/**
101	* Atomically sets the value to the given updated value
102	* if the current value is <a href="#bitEquals">bitwise equal</a>
103	* to the expected value.
104	*
105	* @param expect the expected value
106	* @param update the new value
107	* @return {@code true} if successful. False return indicates that
108	* the actual value was not bitwise equal to the expected value.
109	*/
110	public final boolean compareAndSet(double expect, double update) {
111	return unsafe.compareAndSwapLong(this, valueOffset,
112	doubleToRawLongBits(expect),
113	doubleToRawLongBits(update));
114	}
115
116	/**
117	* Atomically sets the value to the given updated value
118	* if the current value is <a href="#bitEquals">bitwise equal</a>
119	* to the expected value.
120	*
121	* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
122	* and does not provide ordering guarantees, so is only rarely an
123	* appropriate alternative to {@code compareAndSet}.
124	*
125	* @param expect the expected value
126	* @param update the new value
127	* @return {@code true} if successful
128	*/
129	public final boolean weakCompareAndSet(double expect, double update) {
130	return compareAndSet(expect, update);
131	}
132
133	/**
134	* Atomically adds the given value to the current value.
135	*
136	* @param delta the value to add
137	* @return the previous value
138	*/
139	public final double getAndAdd(double delta) {
140	while (true) {
141	long current = value;
142	double currentVal = longBitsToDouble(current);
143	double nextVal = currentVal + delta;
144	long next = doubleToRawLongBits(nextVal);
145	if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
146	return currentVal;
147	}
148	}
149
150	/**
151	* Atomically adds the given value to the current value.
152	*
153	* @param delta the value to add
154	* @return the updated value
155	*/
156	public final double addAndGet(double delta) {
157	while (true) {
158	long current = value;
159	double currentVal = longBitsToDouble(current);
160	double nextVal = currentVal + delta;
161	long next = doubleToRawLongBits(nextVal);
162	if (unsafe.compareAndSwapLong(this, valueOffset, current, next))
163	return nextVal;
164	}
165	}
166
167	/**
168	* Returns the String representation of the current value.
169	* @return the String representation of the current value
170	*/
171	public String toString() {
172	return Double.toString(get());
173	}
174
175	/**
176	* Returns the value of this {@code AtomicDouble} as an {@code int}
177	* after a narrowing primitive conversion.
178	*/
179	public int intValue() {
180	return (int)get();
181	}
182
183	/**
184	* Returns the value of this {@code AtomicDouble} as a {@code long}
185	* after a narrowing primitive conversion.
186	*/
187	public long longValue() {
188	return (long)get();
189	}
190
191	/**
192	* Returns the value of this {@code AtomicDouble} as a {@code float}
193	* after a narrowing primitive conversion.
194	*/
195	public float floatValue() {
196	return (float)get();
197	}
198
199	/**
200	* Returns the value of this {@code AtomicDouble} as a {@code double}.
201	*/
202	public double doubleValue() {
203	return get();
204	}
205
206	// Unsafe mechanics
207	private static final sun.misc.Unsafe unsafe = getUnsafe();
208	private static final long valueOffset;
209
210	static {
211	try {
212	valueOffset = unsafe.objectFieldOffset
213	(AtomicDouble.class.getDeclaredField("value"));
214	} catch (Exception ex) { throw new Error(ex); }
215	}
216
217	/**
218	* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
219	* Replace with a simple call to Unsafe.getUnsafe when integrating
220	* into a jdk.
221	*
222	* @return a sun.misc.Unsafe
223	*/
224	private static sun.misc.Unsafe getUnsafe() {
225	try {
226	return sun.misc.Unsafe.getUnsafe();
227	} catch (SecurityException se) {
228	try {
229	return java.security.AccessController.doPrivileged
230	(new java.security
231	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
232	public sun.misc.Unsafe run() throws Exception {
233	java.lang.reflect.Field f = sun.misc
234	.Unsafe.class.getDeclaredField("theUnsafe");
235	f.setAccessible(true);
236	return (sun.misc.Unsafe) f.get(null);
237	}});
238	} catch (java.security.PrivilegedActionException e) {
239	throw new RuntimeException("Could not initialize intrinsics",
240	e.getCause());
241	}
242	}
243	}
244
245	}