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:	1.9
Committed:	Mon Jan 14 02:02:41 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.8:	+1 -1 lines
Log Message:	punctuation
#	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	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	* 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	*
23	* <p><em>jsr166e note: This class is targeted to be placed in
24	* java.util.concurrent.atomic.</em>
25	*
26	* @since 1.8
27	* @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	* <em>NOT</em> an atomic snapshot; invocation in the absence of
76	* 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	* @return the String representation of the {@link #max}
141	*/
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	* narrowing primitive conversion.
158	*/
159	public long longValue() {
160	return (long)max();
161	}
162
163	/**
164	* Returns the {@link #max} as an {@code int} after a
165	* narrowing primitive conversion.
166	*/
167	public int intValue() {
168	return (int)max();
169	}
170
171	/**
172	* Returns the {@link #max} as a {@code float}
173	* after a narrowing primitive conversion.
174	*/
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	private void readObject(java.io.ObjectInputStream s)
186	throws java.io.IOException, ClassNotFoundException {
187	s.defaultReadObject();
188	busy = 0;
189	cells = null;
190	base = Double.doubleToRawLongBits(s.readDouble());
191	}
192
193	}