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 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(ObjectInputStream s)
        throws IOException, ClassNotFoundException {
        s.defaultReadObject();
        busy = 0;
        cells = null;
        base = Double.doubleToRawLongBits(s.readDouble());
    }

}
Revision:	1.7
Committed:	Sun Jan 6 18:50:00 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.6:	+1 -1 lines
Log Message:	javadoc style
#	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.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 equals}, {@code hashCode} and {@code
23	* compareTo} because instances are expected to be mutated, and so are
24	* not useful as collection keys.
25	*
26	* <p><em>jsr166e note: This class is targeted to be placed in
27	* java.util.concurrent.atomic.</em>
28	*
29	* @since 1.8
30	* @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	* narrowing 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	* narrowing 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 narrowing 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	}