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>
 *
 * @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:	1.1
Committed:	Tue Aug 2 18:04:12 2011 UTC (12 years, 9 months ago) by dl
Branch:	MAIN
Log Message:	Refactor and introduce new forms of update
#	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			* @author Doug Lea
30			*/
31			public class DoubleMaxUpdater extends Striped64 implements Serializable {
32			private static final long serialVersionUID = 7249069246863182397L;
33			/**
34			* Long representation of negative infinity. See class Double
35			* internal documentation for explanation.
36			*/
37			private static final long MIN_AS_LONG = 0xfff0000000000000L;
38
39			/**
40			* Update function. See class DoubleAdder for rationale
41			* for using conversions from/to long.
42			*/
43			final long fn(long v, long x) {
44			return Double.longBitsToDouble(v) > Double.longBitsToDouble(x) ? v : x;
45			}
46
47			/**
48			* Creates a new instance with initial value of {@code
49			* Double.NEGATIVE_INFINITY}.
50			*/
51			public DoubleMaxUpdater() {
52			base = MIN_AS_LONG;
53			}
54
55			/**
56			* Updates the maximum to be at least the given value.
57			*
58			* @param x the value to update
59			*/
60			public void update(double x) {
61			long lx = Double.doubleToRawLongBits(x);
62			Cell[] as; long b, v; HashCode hc; Cell a; int n;
63			if ((as = cells) != null \|\|
64			(Double.longBitsToDouble(b = base) < x && !casBase(b, lx))) {
65			boolean uncontended = true;
66			int h = (hc = threadHashCode.get()).code;
67			if (as == null \|\| (n = as.length) < 1 \|\|
68			(a = as[(n - 1) & h]) == null \|\|
69			(Double.longBitsToDouble(v = a.value) < x &&
70			!(uncontended = a.cas(v, lx))))
71			retryUpdate(lx, hc, uncontended);
72			}
73			}
74
75			/**
76			* Returns the current maximum. The returned value is
77			* <em>NOT</em> an atomic snapshot: Invocation in the absence of
78			* concurrent updates returns an accurate result, but concurrent
79			* updates that occur while the value is being calculated might
80			* not be incorporated.
81			*
82			* @return the maximum
83			*/
84			public double max() {
85			Cell[] as = cells;
86			double max = Double.longBitsToDouble(base);
87			if (as != null) {
88			int n = as.length;
89			double v;
90			for (int i = 0; i < n; ++i) {
91			Cell a = as[i];
92			if (a != null && (v = Double.longBitsToDouble(a.value)) > max)
93			max = v;
94			}
95			}
96			return max;
97			}
98
99			/**
100			* Resets variables maintaining updates to {@code
101			* Double.NEGATIVE_INFINITY}. This method may be a useful
102			* alternative to creating a new updater, but is only effective if
103			* there are no concurrent updates. Because this method is
104			* intrinsically racy, it should only be used when it is known
105			* that no threads are concurrently updating.
106			*/
107			public void reset() {
108			internalReset(MIN_AS_LONG);
109			}
110
111			/**
112			* Equivalent in effect to {@link #max} followed by {@link
113			* #reset}. This method may apply for example during quiescent
114			* points between multithreaded computations. If there are
115			* updates concurrent with this method, the returned value is
116			* <em>not</em> guaranteed to be the final value occurring before
117			* the reset.
118			*
119			* @return the maximum
120			*/
121			public double maxThenReset() {
122			Cell[] as = cells;
123			double max = Double.longBitsToDouble(base);
124			base = MIN_AS_LONG;
125			if (as != null) {
126			int n = as.length;
127			for (int i = 0; i < n; ++i) {
128			Cell a = as[i];
129			if (a != null) {
130			double v = Double.longBitsToDouble(a.value);
131			a.value = MIN_AS_LONG;
132			if (v > max)
133			max = v;
134			}
135			}
136			}
137			return max;
138			}
139
140			/**
141			* Returns the String representation of the {@link #max}.
142			* @return the String representation of the {@link #max}.
143			*/
144			public String toString() {
145			return Double.toString(max());
146			}
147
148			/**
149			* Equivalent to {@link #max}.
150			*
151			* @return the max
152			*/
153			public double doubleValue() {
154			return max();
155			}
156
157			/**
158			* Returns the {@link #max} as a {@code long} after a
159			* primitive conversion.
160			*/
161			public long longValue() {
162			return (long)max();
163			}
164
165			/**
166			* Returns the {@link #max} as an {@code int} after a
167			* primitive conversion.
168			*/
169			public int intValue() {
170			return (int)max();
171			}
172
173			/**
174			* Returns the {@link #max} as a {@code float}
175			* after a primitive conversion.
176			*/
177			public float floatValue() {
178			return (float)max();
179			}
180
181			private void writeObject(java.io.ObjectOutputStream s)
182			throws java.io.IOException {
183			s.defaultWriteObject();
184			s.writeDouble(max());
185			}
186
187			private void readObject(ObjectInputStream s)
188			throws IOException, ClassNotFoundException {
189			s.defaultReadObject();
190			busy = 0;
191			cells = null;
192			base = Double.doubleToRawLongBits(s.readDouble());
193			}
194
195			}