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.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
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; int[] hc; Cell a; int n;
        if ((as = cells) != null ||
            !casBase(b = base,
                     Double.doubleToRawLongBits
                     (Double.longBitsToDouble(b) + x))) {
            boolean uncontended = true;
            if ((hc = threadHashCode.get()) == null ||
                as == null || (n = as.length) < 1 ||
                (a = as[(n - 1) & hc[0]]) == 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 floating-point 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(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        s.writeDouble(sum());
    }

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

}
Revision:	1.12
Committed:	Mon May 5 20:20:15 2014 UTC (9 years, 11 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.11:	+7 -4 lines
Log Message:	import everything to reduce diffs with guava fork
#	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	jsr166	1.12
9			import java.io.IOException;
10			import java.io.ObjectInputStream;
11			import java.io.ObjectOutputStream;
12	dl	1.1	import java.io.Serializable;
13
14			/**
15			* One or more variables that together maintain an initially zero
16			* {@code double} sum. When updates (method {@link #add}) are
17			* contended across threads, the set of variables may grow dynamically
18			* to reduce contention. Method {@link #sum} (or, equivalently {@link
19			* #doubleValue}) returns the current total combined across the
20			* variables maintaining the sum.
21			*
22			* <p>This class extends {@link Number}, but does <em>not</em> define
23	jsr166	1.6	* methods such as {@code equals}, {@code hashCode} and {@code
24			* compareTo} because instances are expected to be mutated, and so are
25			* not useful as collection keys.
26	dl	1.1	*
27			* <p><em>jsr166e note: This class is targeted to be placed in
28	jsr166	1.5	* java.util.concurrent.atomic.</em>
29	dl	1.1	*
30	jsr166	1.2	* @since 1.8
31	dl	1.1	* @author Doug Lea
32			*/
33			public class DoubleAdder extends Striped64 implements Serializable {
34			private static final long serialVersionUID = 7249069246863182397L;
35
36			/**
37			* Update function. Note that we must use "long" for underlying
38			* representations, because there is no compareAndSet for double,
39			* due to the fact that the bitwise equals used in any CAS
40			* implementation is not the same as double-precision equals.
41			* However, we use CAS only to detect and alleviate contention,
42			* for which bitwise equals works best anyway. In principle, the
43			* long/double conversions used here should be essentially free on
44			* most platforms since they just re-interpret bits.
45			*
46			* Similar conversions are used in other methods.
47			*/
48			final long fn(long v, long x) {
49			return Double.doubleToRawLongBits
50			(Double.longBitsToDouble(v) +
51			Double.longBitsToDouble(x));
52			}
53
54			/**
55			* Creates a new adder with initial sum of zero.
56			*/
57			public DoubleAdder() {
58			}
59
60			/**
61			* Adds the given value.
62			*
63			* @param x the value to add
64			*/
65			public void add(double x) {
66	dl	1.11	Cell[] as; long b, v; int[] hc; Cell a; int n;
67	dl	1.1	if ((as = cells) != null \|\|
68			!casBase(b = base,
69			Double.doubleToRawLongBits
70			(Double.longBitsToDouble(b) + x))) {
71			boolean uncontended = true;
72	dl	1.11	if ((hc = threadHashCode.get()) == null \|\|
73			as == null \|\| (n = as.length) < 1 \|\|
74			(a = as[(n - 1) & hc[0]]) == null \|\|
75	dl	1.1	!(uncontended = a.cas(v = a.value,
76			Double.doubleToRawLongBits
77			(Double.longBitsToDouble(v) + x))))
78			retryUpdate(Double.doubleToRawLongBits(x), hc, uncontended);
79			}
80			}
81
82			/**
83			* Returns the current sum. The returned value is <em>NOT</em> an
84	jsr166	1.9	* atomic snapshot; invocation in the absence of concurrent
85	dl	1.1	* updates returns an accurate result, but concurrent updates that
86			* occur while the sum is being calculated might not be
87	jsr166	1.10	* incorporated. Also, because floating-point arithmetic is not
88	dl	1.1	* strictly associative, the returned result need not be identical
89			* to the value that would be obtained in a sequential series of
90			* updates to a single variable.
91			*
92			* @return the sum
93			*/
94			public double sum() {
95			Cell[] as = cells;
96			double sum = Double.longBitsToDouble(base);
97			if (as != null) {
98			int n = as.length;
99			for (int i = 0; i < n; ++i) {
100			Cell a = as[i];
101			if (a != null)
102			sum += Double.longBitsToDouble(a.value);
103			}
104			}
105			return sum;
106			}
107
108			/**
109			* Resets variables maintaining the sum to zero. This method may
110			* be a useful alternative to creating a new adder, but is only
111			* effective if there are no concurrent updates. Because this
112			* method is intrinsically racy, it should only be used when it is
113			* known that no threads are concurrently updating.
114			*/
115			public void reset() {
116			internalReset(0L);
117			}
118
119			/**
120			* Equivalent in effect to {@link #sum} followed by {@link
121			* #reset}. This method may apply for example during quiescent
122			* points between multithreaded computations. If there are
123			* updates concurrent with this method, the returned value is
124			* <em>not</em> guaranteed to be the final value occurring before
125			* the reset.
126			*
127			* @return the sum
128			*/
129			public double sumThenReset() {
130			Cell[] as = cells;
131			double sum = Double.longBitsToDouble(base);
132			base = 0L;
133			if (as != null) {
134			int n = as.length;
135			for (int i = 0; i < n; ++i) {
136			Cell a = as[i];
137			if (a != null) {
138			long v = a.value;
139			a.value = 0L;
140			sum += Double.longBitsToDouble(v);
141			}
142			}
143			}
144			return sum;
145			}
146
147			/**
148			* Returns the String representation of the {@link #sum}.
149	jsr166	1.3	* @return the String representation of the {@link #sum}
150	dl	1.1	*/
151			public String toString() {
152			return Double.toString(sum());
153			}
154
155			/**
156			* Equivalent to {@link #sum}.
157			*
158			* @return the sum
159			*/
160			public double doubleValue() {
161			return sum();
162			}
163
164			/**
165			* Returns the {@link #sum} as a {@code long} after a
166	jsr166	1.4	* narrowing primitive conversion.
167	dl	1.1	*/
168			public long longValue() {
169			return (long)sum();
170			}
171
172			/**
173			* Returns the {@link #sum} as an {@code int} after a
174	jsr166	1.4	* narrowing primitive conversion.
175	dl	1.1	*/
176			public int intValue() {
177			return (int)sum();
178			}
179
180			/**
181			* Returns the {@link #sum} as a {@code float}
182	jsr166	1.4	* after a narrowing primitive conversion.
183	dl	1.1	*/
184			public float floatValue() {
185			return (float)sum();
186			}
187
188	jsr166	1.12	private void writeObject(ObjectOutputStream s) throws IOException {
189	dl	1.1	s.defaultWriteObject();
190			s.writeDouble(sum());
191			}
192
193	jsr166	1.12	private void readObject(ObjectInputStream s)
194			throws IOException, ClassNotFoundException {
195	dl	1.1	s.defaultReadObject();
196			busy = 0;
197			cells = null;
198			base = Double.doubleToRawLongBits(s.readDouble());
199			}
200
201			}