src/jsr166e/DoubleAdder.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;
import java.io.Serializable;

/**
 * One or more variables that together maintain an initially zero
 * {@code double} sum.  When updates (method {@link #add}) are
 * contended across threads, the set of variables may grow dynamically
 * to reduce contention.  Method {@link #sum} (or, equivalently {@link
 * #doubleValue}) returns the current total combined across the
 * variables maintaining the sum.
 *
 * <p>This class extends {@link Number}, but does <em>not</em> define
 * methods such as {@code equals}, {@code hashCode} and {@code
 * compareTo} because instances are expected to be mutated, and so are
 * not useful as collection keys.
 *
 * <p><em>jsr166e note: This class is targeted to be placed in
 * java.util.concurrent.atomic.</em>
 *
 * @since 1.8
 * @author Doug Lea
 */
public class DoubleAdder extends Striped64 implements Serializable {
    private static final long serialVersionUID = 7249069246863182397L;

    /**
     * Update function. Note that we must use "long" for underlying
     * representations, because there is no compareAndSet for double,
     * due to the fact that the bitwise equals used in any CAS
     * implementation is not the same as double-precision equals.
     * However, we use CAS only to detect and alleviate contention,
     * for which bitwise equals works best anyway. In principle, the
     * long/double conversions used here should be essentially free on
     * most platforms since they just re-interpret bits.
     *
     * Similar conversions are used in other methods.
     */
    final long fn(long v, long x) {
        return Double.doubleToRawLongBits
            (Double.longBitsToDouble(v) +
             Double.longBitsToDouble(x));
    }

    /**
     * Creates a new adder with initial sum of zero.
     */
    public DoubleAdder() {
    }

    /**
     * Adds the given value.
     *
     * @param x the value to add
     */
    public void add(double x) {
        Cell[] as; long b, v; HashCode hc; Cell a; int n;
        if ((as = cells) != null ||
            !casBase(b = base,
                     Double.doubleToRawLongBits
                     (Double.longBitsToDouble(b) + x))) {
            boolean uncontended = true;
            int h = (hc = threadHashCode.get()).code;
            if (as == null || (n = as.length) < 1 ||
                (a = as[(n - 1) & h]) == null ||
                !(uncontended = a.cas(v = a.value,
                                      Double.doubleToRawLongBits
                                      (Double.longBitsToDouble(v) + x))))
                retryUpdate(Double.doubleToRawLongBits(x), hc, uncontended);
        }
    }

    /**
     * Returns the current sum.  The returned value is <em>NOT</em> an
     * atomic snapshot: invocation in the absence of concurrent
     * updates returns an accurate result, but concurrent updates that
     * occur while the sum is being calculated might not be
     * incorporated.  Also, because double-precision arithmetic is not
     * strictly associative, the returned result need not be identical
     * to the value that would be obtained in a sequential series of
     * updates to a single variable.
     *
     * @return the sum
     */
    public double sum() {
        Cell[] as = cells;
        double sum = Double.longBitsToDouble(base);
        if (as != null) {
            int n = as.length;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null)
                    sum += Double.longBitsToDouble(a.value);
            }
        }
        return sum;
    }

    /**
     * Resets variables maintaining the sum to zero.  This method may
     * be a useful alternative to creating a new adder, but is only
     * effective if there are no concurrent updates.  Because this
     * method is intrinsically racy, it should only be used when it is
     * known that no threads are concurrently updating.
     */
    public void reset() {
        internalReset(0L);
    }

    /**
     * Equivalent in effect to {@link #sum} followed by {@link
     * #reset}. This method may apply for example during quiescent
     * points between multithreaded computations.  If there are
     * updates concurrent with this method, the returned value is
     * <em>not</em> guaranteed to be the final value occurring before
     * the reset.
     *
     * @return the sum
     */
    public double sumThenReset() {
        Cell[] as = cells;
        double sum = Double.longBitsToDouble(base);
        base = 0L;
        if (as != null) {
            int n = as.length;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null) {
                    long v = a.value;
                    a.value = 0L;
                    sum += Double.longBitsToDouble(v);
                }
            }
        }
        return sum;
    }

    /**
     * Returns the String representation of the {@link #sum}.
     * @return the String representation of the {@link #sum}
     */
    public String toString() {
        return Double.toString(sum());
    }

    /**
     * Equivalent to {@link #sum}.
     *
     * @return the sum
     */
    public double doubleValue() {
        return sum();
    }

    /**
     * Returns the {@link #sum} as a {@code long} after a
     * narrowing primitive conversion.
     */
    public long longValue() {
        return (long)sum();
    }

    /**
     * Returns the {@link #sum} as an {@code int} after a
     * narrowing primitive conversion.
     */
    public int intValue() {
        return (int)sum();
    }

    /**
     * Returns the {@link #sum} as a {@code float}
     * after a narrowing primitive conversion.
     */
    public float floatValue() {
        return (float)sum();
    }

    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
        s.writeDouble(sum());
    }

    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();
        busy = 0;
        cells = null;
        base = Double.doubleToRawLongBits(s.readDouble());
    }

}
Revision:	1.8
Committed:	Mon Jan 7 07:14:01 2013 UTC (11 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.7:	+2 -5 lines
Log Message:	consistent style for readObject
#	User	Rev	Content
1	dl	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;
8			import java.io.Serializable;
9
10			/**
11			* One or more variables that together maintain an initially zero
12			* {@code double} sum. When updates (method {@link #add}) are
13			* contended across threads, the set of variables may grow dynamically
14			* to reduce contention. Method {@link #sum} (or, equivalently {@link
15			* #doubleValue}) returns the current total combined across the
16			* variables maintaining the sum.
17			*
18			* <p>This class extends {@link Number}, but does <em>not</em> define
19	jsr166	1.6	* methods such as {@code equals}, {@code hashCode} and {@code
20			* compareTo} because instances are expected to be mutated, and so are
21			* not useful as collection keys.
22	dl	1.1	*
23			* <p><em>jsr166e note: This class is targeted to be placed in
24	jsr166	1.5	* java.util.concurrent.atomic.</em>
25	dl	1.1	*
26	jsr166	1.2	* @since 1.8
27	dl	1.1	* @author Doug Lea
28			*/
29			public class DoubleAdder extends Striped64 implements Serializable {
30			private static final long serialVersionUID = 7249069246863182397L;
31
32			/**
33			* Update function. Note that we must use "long" for underlying
34			* representations, because there is no compareAndSet for double,
35			* due to the fact that the bitwise equals used in any CAS
36			* implementation is not the same as double-precision equals.
37			* However, we use CAS only to detect and alleviate contention,
38			* for which bitwise equals works best anyway. In principle, the
39			* long/double conversions used here should be essentially free on
40			* most platforms since they just re-interpret bits.
41			*
42			* Similar conversions are used in other methods.
43			*/
44			final long fn(long v, long x) {
45			return Double.doubleToRawLongBits
46			(Double.longBitsToDouble(v) +
47			Double.longBitsToDouble(x));
48			}
49
50			/**
51			* Creates a new adder with initial sum of zero.
52			*/
53			public DoubleAdder() {
54			}
55
56			/**
57			* Adds the given value.
58			*
59			* @param x the value to add
60			*/
61			public void add(double x) {
62			Cell[] as; long b, v; HashCode hc; Cell a; int n;
63			if ((as = cells) != null \|\|
64			!casBase(b = base,
65			Double.doubleToRawLongBits
66			(Double.longBitsToDouble(b) + x))) {
67			boolean uncontended = true;
68			int h = (hc = threadHashCode.get()).code;
69			if (as == null \|\| (n = as.length) < 1 \|\|
70			(a = as[(n - 1) & h]) == null \|\|
71			!(uncontended = a.cas(v = a.value,
72			Double.doubleToRawLongBits
73			(Double.longBitsToDouble(v) + x))))
74			retryUpdate(Double.doubleToRawLongBits(x), hc, uncontended);
75			}
76			}
77
78			/**
79			* Returns the current sum. The returned value is <em>NOT</em> an
80	jsr166	1.7	* atomic snapshot: invocation in the absence of concurrent
81	dl	1.1	* updates returns an accurate result, but concurrent updates that
82			* occur while the sum is being calculated might not be
83			* incorporated. Also, because double-precision arithmetic is not
84			* strictly associative, the returned result need not be identical
85			* to the value that would be obtained in a sequential series of
86			* updates to a single variable.
87			*
88			* @return the sum
89			*/
90			public double sum() {
91			Cell[] as = cells;
92			double sum = Double.longBitsToDouble(base);
93			if (as != null) {
94			int n = as.length;
95			for (int i = 0; i < n; ++i) {
96			Cell a = as[i];
97			if (a != null)
98			sum += Double.longBitsToDouble(a.value);
99			}
100			}
101			return sum;
102			}
103
104			/**
105			* Resets variables maintaining the sum to zero. This method may
106			* be a useful alternative to creating a new adder, but is only
107			* effective if there are no concurrent updates. Because this
108			* method is intrinsically racy, it should only be used when it is
109			* known that no threads are concurrently updating.
110			*/
111			public void reset() {
112			internalReset(0L);
113			}
114
115			/**
116			* Equivalent in effect to {@link #sum} followed by {@link
117			* #reset}. This method may apply for example during quiescent
118			* points between multithreaded computations. If there are
119			* updates concurrent with this method, the returned value is
120			* <em>not</em> guaranteed to be the final value occurring before
121			* the reset.
122			*
123			* @return the sum
124			*/
125			public double sumThenReset() {
126			Cell[] as = cells;
127			double sum = Double.longBitsToDouble(base);
128			base = 0L;
129			if (as != null) {
130			int n = as.length;
131			for (int i = 0; i < n; ++i) {
132			Cell a = as[i];
133			if (a != null) {
134			long v = a.value;
135			a.value = 0L;
136			sum += Double.longBitsToDouble(v);
137			}
138			}
139			}
140			return sum;
141			}
142
143			/**
144			* Returns the String representation of the {@link #sum}.
145	jsr166	1.3	* @return the String representation of the {@link #sum}
146	dl	1.1	*/
147			public String toString() {
148			return Double.toString(sum());
149			}
150
151			/**
152			* Equivalent to {@link #sum}.
153			*
154			* @return the sum
155			*/
156			public double doubleValue() {
157			return sum();
158			}
159
160			/**
161			* Returns the {@link #sum} as a {@code long} after a
162	jsr166	1.4	* narrowing primitive conversion.
163	dl	1.1	*/
164			public long longValue() {
165			return (long)sum();
166			}
167
168			/**
169			* Returns the {@link #sum} as an {@code int} after a
170	jsr166	1.4	* narrowing primitive conversion.
171	dl	1.1	*/
172			public int intValue() {
173			return (int)sum();
174			}
175
176			/**
177			* Returns the {@link #sum} as a {@code float}
178	jsr166	1.4	* after a narrowing primitive conversion.
179	dl	1.1	*/
180			public float floatValue() {
181			return (float)sum();
182			}
183
184			private void writeObject(java.io.ObjectOutputStream s)
185			throws java.io.IOException {
186			s.defaultWriteObject();
187			s.writeDouble(sum());
188			}
189
190	jsr166	1.8	private void readObject(java.io.ObjectInputStream s)
191			throws java.io.IOException, ClassNotFoundException {
192	dl	1.1	s.defaultReadObject();
193			busy = 0;
194			cells = null;
195			base = Double.doubleToRawLongBits(s.readDouble());
196			}
197
198			}