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
#	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 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	}