src/jsr166e/DoubleMaxUpdater.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 a running {@code double}
 * maximum with initial value {@code Double.NEGATIVE_INFINITY}.  When
 * updates (method {@link #update}) are contended across threads, the
 * set of variables may grow dynamically to reduce contention.  Method
 * {@link #max} (or, equivalently, {@link #doubleValue}) returns the
 * current maximum across the variables maintaining updates.
 *
 * <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 DoubleMaxUpdater extends Striped64 implements Serializable {
    private static final long serialVersionUID = 7249069246863182397L;
    /**
     * Long representation of negative infinity. See class Double
     * internal documentation for explanation.
     */
    private static final long MIN_AS_LONG = 0xfff0000000000000L;

    /**
     * Update function. See class DoubleAdder for rationale
     * for using conversions from/to long.
     */
    final long fn(long v, long x) {
        return Double.longBitsToDouble(v) > Double.longBitsToDouble(x) ? v : x;
    }

    /**
     * Creates a new instance with initial value of {@code
     * Double.NEGATIVE_INFINITY}.
     */
    public DoubleMaxUpdater() {
        base = MIN_AS_LONG;
    }

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

    /**
     * Returns the current maximum.  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 value is being calculated might
     * not be incorporated.
     *
     * @return the maximum
     */
    public double max() {
        Cell[] as = cells;
        double max = Double.longBitsToDouble(base);
        if (as != null) {
            int n = as.length;
            double v;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null && (v = Double.longBitsToDouble(a.value)) > max)
                    max = v;
            }
        }
        return max;
    }

    /**
     * Resets variables maintaining updates to {@code
     * Double.NEGATIVE_INFINITY}.  This method may be a useful
     * alternative to creating a new updater, 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(MIN_AS_LONG);
    }

    /**
     * Equivalent in effect to {@link #max} 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 maximum
     */
    public double maxThenReset() {
        Cell[] as = cells;
        double max = Double.longBitsToDouble(base);
        base = MIN_AS_LONG;
        if (as != null) {
            int n = as.length;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null) {
                    double v = Double.longBitsToDouble(a.value);
                    a.value = MIN_AS_LONG;
                    if (v > max)
                        max = v;
                }
            }
        }
        return max;
    }

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

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

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

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

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

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

    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, 4 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 a running {@code double}
12			* maximum with initial value {@code Double.NEGATIVE_INFINITY}. When
13			* updates (method {@link #update}) are contended across threads, the
14			* set of variables may grow dynamically to reduce contention. Method
15			* {@link #max} (or, equivalently, {@link #doubleValue}) returns the
16			* current maximum across the variables maintaining updates.
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 DoubleMaxUpdater extends Striped64 implements Serializable {
30			private static final long serialVersionUID = 7249069246863182397L;
31			/**
32			* Long representation of negative infinity. See class Double
33			* internal documentation for explanation.
34			*/
35			private static final long MIN_AS_LONG = 0xfff0000000000000L;
36
37			/**
38			* Update function. See class DoubleAdder for rationale
39			* for using conversions from/to long.
40			*/
41			final long fn(long v, long x) {
42			return Double.longBitsToDouble(v) > Double.longBitsToDouble(x) ? v : x;
43			}
44
45			/**
46			* Creates a new instance with initial value of {@code
47			* Double.NEGATIVE_INFINITY}.
48			*/
49			public DoubleMaxUpdater() {
50			base = MIN_AS_LONG;
51			}
52
53			/**
54			* Updates the maximum to be at least the given value.
55			*
56			* @param x the value to update
57			*/
58			public void update(double x) {
59			long lx = Double.doubleToRawLongBits(x);
60			Cell[] as; long b, v; HashCode hc; Cell a; int n;
61			if ((as = cells) != null \|\|
62			(Double.longBitsToDouble(b = base) < x && !casBase(b, lx))) {
63			boolean uncontended = true;
64			int h = (hc = threadHashCode.get()).code;
65			if (as == null \|\| (n = as.length) < 1 \|\|
66			(a = as[(n - 1) & h]) == null \|\|
67			(Double.longBitsToDouble(v = a.value) < x &&
68			!(uncontended = a.cas(v, lx))))
69			retryUpdate(lx, hc, uncontended);
70			}
71			}
72
73			/**
74			* Returns the current maximum. The returned value is
75	jsr166	1.7	* <em>NOT</em> an atomic snapshot: invocation in the absence of
76	dl	1.1	* concurrent updates returns an accurate result, but concurrent
77			* updates that occur while the value is being calculated might
78			* not be incorporated.
79			*
80			* @return the maximum
81			*/
82			public double max() {
83			Cell[] as = cells;
84			double max = Double.longBitsToDouble(base);
85			if (as != null) {
86			int n = as.length;
87			double v;
88			for (int i = 0; i < n; ++i) {
89			Cell a = as[i];
90			if (a != null && (v = Double.longBitsToDouble(a.value)) > max)
91			max = v;
92			}
93			}
94			return max;
95			}
96
97			/**
98			* Resets variables maintaining updates to {@code
99			* Double.NEGATIVE_INFINITY}. This method may be a useful
100			* alternative to creating a new updater, but is only effective if
101			* there are no concurrent updates. Because this method is
102			* intrinsically racy, it should only be used when it is known
103			* that no threads are concurrently updating.
104			*/
105			public void reset() {
106			internalReset(MIN_AS_LONG);
107			}
108
109			/**
110			* Equivalent in effect to {@link #max} followed by {@link
111			* #reset}. This method may apply for example during quiescent
112			* points between multithreaded computations. If there are
113			* updates concurrent with this method, the returned value is
114			* <em>not</em> guaranteed to be the final value occurring before
115			* the reset.
116			*
117			* @return the maximum
118			*/
119			public double maxThenReset() {
120			Cell[] as = cells;
121			double max = Double.longBitsToDouble(base);
122			base = MIN_AS_LONG;
123			if (as != null) {
124			int n = as.length;
125			for (int i = 0; i < n; ++i) {
126			Cell a = as[i];
127			if (a != null) {
128			double v = Double.longBitsToDouble(a.value);
129			a.value = MIN_AS_LONG;
130			if (v > max)
131			max = v;
132			}
133			}
134			}
135			return max;
136			}
137
138			/**
139			* Returns the String representation of the {@link #max}.
140	jsr166	1.3	* @return the String representation of the {@link #max}
141	dl	1.1	*/
142			public String toString() {
143			return Double.toString(max());
144			}
145
146			/**
147			* Equivalent to {@link #max}.
148			*
149			* @return the max
150			*/
151			public double doubleValue() {
152			return max();
153			}
154
155			/**
156			* Returns the {@link #max} as a {@code long} after a
157	jsr166	1.4	* narrowing primitive conversion.
158	dl	1.1	*/
159			public long longValue() {
160			return (long)max();
161			}
162
163			/**
164			* Returns the {@link #max} as an {@code int} after a
165	jsr166	1.4	* narrowing primitive conversion.
166	dl	1.1	*/
167			public int intValue() {
168			return (int)max();
169			}
170
171			/**
172			* Returns the {@link #max} as a {@code float}
173	jsr166	1.4	* after a narrowing primitive conversion.
174	dl	1.1	*/
175			public float floatValue() {
176			return (float)max();
177			}
178
179			private void writeObject(java.io.ObjectOutputStream s)
180			throws java.io.IOException {
181			s.defaultWriteObject();
182			s.writeDouble(max());
183			}
184
185	jsr166	1.8	private void readObject(java.io.ObjectInputStream s)
186			throws java.io.IOException, ClassNotFoundException {
187	dl	1.1	s.defaultReadObject();
188			busy = 0;
189			cells = null;
190			base = Double.doubleToRawLongBits(s.readDouble());
191			}
192
193			}