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.Serializable;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

/**
 * 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 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
     * primitive conversion.
     */
    public long longValue() {
        return (long)max();
    }

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

    /**
     * Returns the {@link #max} as a {@code float}
     * after a 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(ObjectInputStream s)
        throws IOException, ClassNotFoundException {
        s.defaultReadObject();
        busy = 0;
        cells = null;
        base = Double.doubleToRawLongBits(s.readDouble());
    }

}
Revision:	1.2
Committed:	Sat Sep 10 01:38:28 2011 UTC (12 years, 8 months ago) by jsr166
Branch:	MAIN
Changes since 1.1:	+1 -0 lines
Log Message:	fix up @since
#	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.IOException;
9			import java.io.Serializable;
10			import java.io.ObjectInputStream;
11			import java.io.ObjectOutputStream;
12
13			/**
14			* One or more variables that together maintain a running {@code double}
15			* maximum with initial value {@code Double.NEGATIVE_INFINITY}. When
16			* updates (method {@link #update}) are contended across threads, the
17			* set of variables may grow dynamically to reduce contention. Method
18			* {@link #max} (or, equivalently, {@link #doubleValue}) returns the
19			* current maximum across the variables maintaining updates.
20			*
21			* <p>This class extends {@link Number}, but does <em>not</em> define
22			* methods such as {@code hashCode} and {@code compareTo} because
23			* instances are expected to be mutated, and so are not useful as
24			* collection keys.
25			*
26			* <p><em>jsr166e note: This class is targeted to be placed in
27			* java.util.concurrent.atomic<em>
28			*
29	jsr166	1.2	* @since 1.8
30	dl	1.1	* @author Doug Lea
31			*/
32			public class DoubleMaxUpdater extends Striped64 implements Serializable {
33			private static final long serialVersionUID = 7249069246863182397L;
34			/**
35			* Long representation of negative infinity. See class Double
36			* internal documentation for explanation.
37			*/
38			private static final long MIN_AS_LONG = 0xfff0000000000000L;
39
40			/**
41			* Update function. See class DoubleAdder for rationale
42			* for using conversions from/to long.
43			*/
44			final long fn(long v, long x) {
45			return Double.longBitsToDouble(v) > Double.longBitsToDouble(x) ? v : x;
46			}
47
48			/**
49			* Creates a new instance with initial value of {@code
50			* Double.NEGATIVE_INFINITY}.
51			*/
52			public DoubleMaxUpdater() {
53			base = MIN_AS_LONG;
54			}
55
56			/**
57			* Updates the maximum to be at least the given value.
58			*
59			* @param x the value to update
60			*/
61			public void update(double x) {
62			long lx = Double.doubleToRawLongBits(x);
63			Cell[] as; long b, v; HashCode hc; Cell a; int n;
64			if ((as = cells) != null \|\|
65			(Double.longBitsToDouble(b = base) < x && !casBase(b, lx))) {
66			boolean uncontended = true;
67			int h = (hc = threadHashCode.get()).code;
68			if (as == null \|\| (n = as.length) < 1 \|\|
69			(a = as[(n - 1) & h]) == null \|\|
70			(Double.longBitsToDouble(v = a.value) < x &&
71			!(uncontended = a.cas(v, lx))))
72			retryUpdate(lx, hc, uncontended);
73			}
74			}
75
76			/**
77			* Returns the current maximum. The returned value is
78			* <em>NOT</em> an atomic snapshot: Invocation in the absence of
79			* concurrent updates returns an accurate result, but concurrent
80			* updates that occur while the value is being calculated might
81			* not be incorporated.
82			*
83			* @return the maximum
84			*/
85			public double max() {
86			Cell[] as = cells;
87			double max = Double.longBitsToDouble(base);
88			if (as != null) {
89			int n = as.length;
90			double v;
91			for (int i = 0; i < n; ++i) {
92			Cell a = as[i];
93			if (a != null && (v = Double.longBitsToDouble(a.value)) > max)
94			max = v;
95			}
96			}
97			return max;
98			}
99
100			/**
101			* Resets variables maintaining updates to {@code
102			* Double.NEGATIVE_INFINITY}. This method may be a useful
103			* alternative to creating a new updater, but is only effective if
104			* there are no concurrent updates. Because this method is
105			* intrinsically racy, it should only be used when it is known
106			* that no threads are concurrently updating.
107			*/
108			public void reset() {
109			internalReset(MIN_AS_LONG);
110			}
111
112			/**
113			* Equivalent in effect to {@link #max} followed by {@link
114			* #reset}. This method may apply for example during quiescent
115			* points between multithreaded computations. If there are
116			* updates concurrent with this method, the returned value is
117			* <em>not</em> guaranteed to be the final value occurring before
118			* the reset.
119			*
120			* @return the maximum
121			*/
122			public double maxThenReset() {
123			Cell[] as = cells;
124			double max = Double.longBitsToDouble(base);
125			base = MIN_AS_LONG;
126			if (as != null) {
127			int n = as.length;
128			for (int i = 0; i < n; ++i) {
129			Cell a = as[i];
130			if (a != null) {
131			double v = Double.longBitsToDouble(a.value);
132			a.value = MIN_AS_LONG;
133			if (v > max)
134			max = v;
135			}
136			}
137			}
138			return max;
139			}
140
141			/**
142			* Returns the String representation of the {@link #max}.
143			* @return the String representation of the {@link #max}.
144			*/
145			public String toString() {
146			return Double.toString(max());
147			}
148
149			/**
150			* Equivalent to {@link #max}.
151			*
152			* @return the max
153			*/
154			public double doubleValue() {
155			return max();
156			}
157
158			/**
159			* Returns the {@link #max} as a {@code long} after a
160			* primitive conversion.
161			*/
162			public long longValue() {
163			return (long)max();
164			}
165
166			/**
167			* Returns the {@link #max} as an {@code int} after a
168			* primitive conversion.
169			*/
170			public int intValue() {
171			return (int)max();
172			}
173
174			/**
175			* Returns the {@link #max} as a {@code float}
176			* after a primitive conversion.
177			*/
178			public float floatValue() {
179			return (float)max();
180			}
181
182			private void writeObject(java.io.ObjectOutputStream s)
183			throws java.io.IOException {
184			s.defaultWriteObject();
185			s.writeDouble(max());
186			}
187
188			private void readObject(ObjectInputStream s)
189			throws IOException, ClassNotFoundException {
190			s.defaultReadObject();
191			busy = 0;
192			cells = null;
193			base = Double.doubleToRawLongBits(s.readDouble());
194			}
195
196			}