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

    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 (10 years 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 a running {@code double}
16			* maximum with initial value {@code Double.NEGATIVE_INFINITY}. When
17			* updates (method {@link #update}) are contended across threads, the
18			* set of variables may grow dynamically to reduce contention. Method
19			* {@link #max} (or, equivalently, {@link #doubleValue}) returns the
20			* current maximum across the variables maintaining updates.
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 DoubleMaxUpdater extends Striped64 implements Serializable {
34			private static final long serialVersionUID = 7249069246863182397L;
35			/**
36			* Long representation of negative infinity. See class Double
37			* internal documentation for explanation.
38			*/
39			private static final long MIN_AS_LONG = 0xfff0000000000000L;
40
41			/**
42			* Update function. See class DoubleAdder for rationale
43			* for using conversions from/to long.
44			*/
45			final long fn(long v, long x) {
46			return Double.longBitsToDouble(v) > Double.longBitsToDouble(x) ? v : x;
47			}
48
49			/**
50			* Creates a new instance with initial value of {@code
51			* Double.NEGATIVE_INFINITY}.
52			*/
53			public DoubleMaxUpdater() {
54			base = MIN_AS_LONG;
55			}
56
57			/**
58			* Updates the maximum to be at least the given value.
59			*
60			* @param x the value to update
61			*/
62			public void update(double x) {
63			long lx = Double.doubleToRawLongBits(x);
64	dl	1.10	Cell[] as; long b, v; int[] hc; Cell a; int n;
65	dl	1.1	if ((as = cells) != null \|\|
66			(Double.longBitsToDouble(b = base) < x && !casBase(b, lx))) {
67			boolean uncontended = true;
68	jsr166	1.11	if ((hc = threadHashCode.get()) == null \|\|
69	dl	1.10	as == null \|\| (n = as.length) < 1 \|\|
70			(a = as[(n - 1) & hc[0]]) == null \|\|
71	dl	1.1	(Double.longBitsToDouble(v = a.value) < x &&
72			!(uncontended = a.cas(v, lx))))
73			retryUpdate(lx, hc, uncontended);
74			}
75			}
76
77			/**
78			* Returns the current maximum. The returned value is
79	jsr166	1.9	* <em>NOT</em> an atomic snapshot; invocation in the absence of
80	dl	1.1	* concurrent updates returns an accurate result, but concurrent
81			* updates that occur while the value is being calculated might
82			* not be incorporated.
83			*
84			* @return the maximum
85			*/
86			public double max() {
87			Cell[] as = cells;
88			double max = Double.longBitsToDouble(base);
89			if (as != null) {
90			int n = as.length;
91			double v;
92			for (int i = 0; i < n; ++i) {
93			Cell a = as[i];
94			if (a != null && (v = Double.longBitsToDouble(a.value)) > max)
95			max = v;
96			}
97			}
98			return max;
99			}
100
101			/**
102			* Resets variables maintaining updates to {@code
103			* Double.NEGATIVE_INFINITY}. This method may be a useful
104			* alternative to creating a new updater, but is only effective if
105			* there are no concurrent updates. Because this method is
106			* intrinsically racy, it should only be used when it is known
107			* that no threads are concurrently updating.
108			*/
109			public void reset() {
110			internalReset(MIN_AS_LONG);
111			}
112
113			/**
114			* Equivalent in effect to {@link #max} followed by {@link
115			* #reset}. This method may apply for example during quiescent
116			* points between multithreaded computations. If there are
117			* updates concurrent with this method, the returned value is
118			* <em>not</em> guaranteed to be the final value occurring before
119			* the reset.
120			*
121			* @return the maximum
122			*/
123			public double maxThenReset() {
124			Cell[] as = cells;
125			double max = Double.longBitsToDouble(base);
126			base = MIN_AS_LONG;
127			if (as != null) {
128			int n = as.length;
129			for (int i = 0; i < n; ++i) {
130			Cell a = as[i];
131			if (a != null) {
132			double v = Double.longBitsToDouble(a.value);
133			a.value = MIN_AS_LONG;
134			if (v > max)
135			max = v;
136			}
137			}
138			}
139			return max;
140			}
141
142			/**
143			* Returns the String representation of the {@link #max}.
144	jsr166	1.3	* @return the String representation of the {@link #max}
145	dl	1.1	*/
146			public String toString() {
147			return Double.toString(max());
148			}
149
150			/**
151			* Equivalent to {@link #max}.
152			*
153			* @return the max
154			*/
155			public double doubleValue() {
156			return max();
157			}
158
159			/**
160			* Returns the {@link #max} as a {@code long} after a
161	jsr166	1.4	* narrowing primitive conversion.
162	dl	1.1	*/
163			public long longValue() {
164			return (long)max();
165			}
166
167			/**
168			* Returns the {@link #max} as an {@code int} after a
169	jsr166	1.4	* narrowing primitive conversion.
170	dl	1.1	*/
171			public int intValue() {
172			return (int)max();
173			}
174
175			/**
176			* Returns the {@link #max} as a {@code float}
177	jsr166	1.4	* after a narrowing primitive conversion.
178	dl	1.1	*/
179			public float floatValue() {
180			return (float)max();
181			}
182
183	jsr166	1.12	private void writeObject(ObjectOutputStream s) throws IOException {
184	dl	1.1	s.defaultWriteObject();
185			s.writeDouble(max());
186			}
187
188	jsr166	1.12	private void readObject(ObjectInputStream s)
189			throws IOException, ClassNotFoundException {
190	dl	1.1	s.defaultReadObject();
191			busy = 0;
192			cells = null;
193			base = Double.doubleToRawLongBits(s.readDouble());
194			}
195
196			}