src/jsr166e/LongMaxUpdater.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 long}
 * maximum with initial value {@code Long.MIN_VALUE}.  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 #longValue}) 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>
 *
 * @since 1.8
 * @author Doug Lea
 */
public class LongMaxUpdater extends Striped64 implements Serializable {
    private static final long serialVersionUID = 7249069246863182397L;

    /**
     * Version of max for use in retryUpdate
     */
    final long fn(long v, long x) { return v > x ? v : x; }

    /**
     * Creates a new instance with initial maximum of {@code
     * Long.MIN_VALUE}.
     */
    public LongMaxUpdater() {
        base = Long.MIN_VALUE;
    }

    /**
     * Updates the maximum to be at least the given value.
     *
     * @param x the value to update
     */
    public void update(long x) {
        Cell[] as; long b, v; HashCode hc; Cell a; int n;
        if ((as = cells) != null ||
            (b = base) < x && !casBase(b, x)) {
            boolean uncontended = true;
            int h = (hc = threadHashCode.get()).code;
            if (as == null || (n = as.length) < 1 ||
                (a = as[(n - 1) & h]) == null ||
                ((v = a.value) < x && !(uncontended = a.cas(v, x))))
                retryUpdate(x, 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 long max() {
        Cell[] as = cells;
        long max = base;
        if (as != null) {
            int n = as.length;
            long v;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null && (v = a.value) > max)
                    max = v;
            }
        }
        return max;
    }

    /**
     * Resets variables maintaining updates to {@code Long.MIN_VALUE}.
     * 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(Long.MIN_VALUE);
    }

    /**
     * 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 long maxThenReset() {
        Cell[] as = cells;
        long max = base;
        base = Long.MIN_VALUE;
        if (as != null) {
            int n = as.length;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null) {
                    long v = a.value;
                    a.value = Long.MIN_VALUE;
                    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 Long.toString(max());
    }

    /**
     * Equivalent to {@link #max}.
     *
     * @return the maximum
     */
    public long longValue() {
        return 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 widening primitive conversion.
     */
    public float floatValue() {
        return (float)max();
    }

    /**
     * Returns the {@link #max} as a {@code double} after a widening
     * primitive conversion.
     */
    public double doubleValue() {
        return (double)max();
    }

    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
        s.writeLong(max());
    }

    private void readObject(ObjectInputStream s)
        throws IOException, ClassNotFoundException {
        s.defaultReadObject();
        busy = 0;
        cells = null;
        base = s.readLong();
    }

}
Revision:	1.3
Committed:	Sat Sep 10 01:44:53 2011 UTC (12 years, 8 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+1 -1 lines
Log Message:	standardized javadoc 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.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 long}
15	* maximum with initial value {@code Long.MIN_VALUE}. When updates
16	* (method {@link #update}) are contended across threads, the set of
17	* variables may grow dynamically to reduce contention. Method {@link
18	* #max} (or, equivalently, {@link #longValue}) returns the current
19	* 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	* @since 1.8
30	* @author Doug Lea
31	*/
32	public class LongMaxUpdater extends Striped64 implements Serializable {
33	private static final long serialVersionUID = 7249069246863182397L;
34
35	/**
36	* Version of max for use in retryUpdate
37	*/
38	final long fn(long v, long x) { return v > x ? v : x; }
39
40	/**
41	* Creates a new instance with initial maximum of {@code
42	* Long.MIN_VALUE}.
43	*/
44	public LongMaxUpdater() {
45	base = Long.MIN_VALUE;
46	}
47
48	/**
49	* Updates the maximum to be at least the given value.
50	*
51	* @param x the value to update
52	*/
53	public void update(long x) {
54	Cell[] as; long b, v; HashCode hc; Cell a; int n;
55	if ((as = cells) != null \|\|
56	(b = base) < x && !casBase(b, x)) {
57	boolean uncontended = true;
58	int h = (hc = threadHashCode.get()).code;
59	if (as == null \|\| (n = as.length) < 1 \|\|
60	(a = as[(n - 1) & h]) == null \|\|
61	((v = a.value) < x && !(uncontended = a.cas(v, x))))
62	retryUpdate(x, hc, uncontended);
63	}
64	}
65
66	/**
67	* Returns the current maximum. The returned value is
68	* <em>NOT</em> an atomic snapshot: Invocation in the absence of
69	* concurrent updates returns an accurate result, but concurrent
70	* updates that occur while the value is being calculated might
71	* not be incorporated.
72	*
73	* @return the maximum
74	*/
75	public long max() {
76	Cell[] as = cells;
77	long max = base;
78	if (as != null) {
79	int n = as.length;
80	long v;
81	for (int i = 0; i < n; ++i) {
82	Cell a = as[i];
83	if (a != null && (v = a.value) > max)
84	max = v;
85	}
86	}
87	return max;
88	}
89
90	/**
91	* Resets variables maintaining updates to {@code Long.MIN_VALUE}.
92	* This method may be a useful alternative to creating a new
93	* updater, but is only effective if there are no concurrent
94	* updates. Because this method is intrinsically racy, it should
95	* only be used when it is known that no threads are concurrently
96	* updating.
97	*/
98	public void reset() {
99	internalReset(Long.MIN_VALUE);
100	}
101
102	/**
103	* Equivalent in effect to {@link #max} followed by {@link
104	* #reset}. This method may apply for example during quiescent
105	* points between multithreaded computations. If there are
106	* updates concurrent with this method, the returned value is
107	* <em>not</em> guaranteed to be the final value occurring before
108	* the reset.
109	*
110	* @return the maximum
111	*/
112	public long maxThenReset() {
113	Cell[] as = cells;
114	long max = base;
115	base = Long.MIN_VALUE;
116	if (as != null) {
117	int n = as.length;
118	for (int i = 0; i < n; ++i) {
119	Cell a = as[i];
120	if (a != null) {
121	long v = a.value;
122	a.value = Long.MIN_VALUE;
123	if (v > max)
124	max = v;
125	}
126	}
127	}
128	return max;
129	}
130
131	/**
132	* Returns the String representation of the {@link #max}.
133	* @return the String representation of the {@link #max}
134	*/
135	public String toString() {
136	return Long.toString(max());
137	}
138
139	/**
140	* Equivalent to {@link #max}.
141	*
142	* @return the maximum
143	*/
144	public long longValue() {
145	return max();
146	}
147
148	/**
149	* Returns the {@link #max} as an {@code int} after a narrowing
150	* primitive conversion.
151	*/
152	public int intValue() {
153	return (int)max();
154	}
155
156	/**
157	* Returns the {@link #max} as a {@code float}
158	* after a widening primitive conversion.
159	*/
160	public float floatValue() {
161	return (float)max();
162	}
163
164	/**
165	* Returns the {@link #max} as a {@code double} after a widening
166	* primitive conversion.
167	*/
168	public double doubleValue() {
169	return (double)max();
170	}
171
172	private void writeObject(java.io.ObjectOutputStream s)
173	throws java.io.IOException {
174	s.defaultWriteObject();
175	s.writeLong(max());
176	}
177
178	private void readObject(ObjectInputStream s)
179	throws IOException, ClassNotFoundException {
180	s.defaultReadObject();
181	busy = 0;
182	cells = null;
183	base = s.readLong();
184	}
185
186	}