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 (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
#	Content
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
9	import java.io.IOException;
10	import java.io.ObjectInputStream;
11	import java.io.ObjectOutputStream;
12	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	* 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	*
27	* <p><em>jsr166e note: This class is targeted to be placed in
28	* java.util.concurrent.atomic.</em>
29	*
30	* @since 1.8
31	* @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	Cell[] as; long b, v; int[] hc; Cell a; int n;
65	if ((as = cells) != null \|\|
66	(Double.longBitsToDouble(b = base) < x && !casBase(b, lx))) {
67	boolean uncontended = true;
68	if ((hc = threadHashCode.get()) == null \|\|
69	as == null \|\| (n = as.length) < 1 \|\|
70	(a = as[(n - 1) & hc[0]]) == null \|\|
71	(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	* <em>NOT</em> an atomic snapshot; invocation in the absence of
80	* 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	* @return the String representation of the {@link #max}
145	*/
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	* narrowing primitive conversion.
162	*/
163	public long longValue() {
164	return (long)max();
165	}
166
167	/**
168	* Returns the {@link #max} as an {@code int} after a
169	* narrowing primitive conversion.
170	*/
171	public int intValue() {
172	return (int)max();
173	}
174
175	/**
176	* Returns the {@link #max} as a {@code float}
177	* after a narrowing primitive conversion.
178	*/
179	public float floatValue() {
180	return (float)max();
181	}
182
183	private void writeObject(ObjectOutputStream s) throws 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	}