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.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * 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 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 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; int[] hc; Cell a; int n;
        if ((as = cells) != null ||
            (b = base) < x && !casBase(b, x)) {
            boolean uncontended = true;
            if ((hc = threadHashCode.get()) == null ||
                as == null || (n = as.length) < 1 ||
                (a = as[(n - 1) & hc[0]]) == 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(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        s.writeLong(max());
    }

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

}
Revision:	1.11
Committed:	Mon May 5 20:20:15 2014 UTC (9 years, 11 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.10:	+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 long}
16	* maximum with initial value {@code Long.MIN_VALUE}. When updates
17	* (method {@link #update}) are contended across threads, the set of
18	* variables may grow dynamically to reduce contention. Method {@link
19	* #max} (or, equivalently, {@link #longValue}) returns the current
20	* 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 LongMaxUpdater extends Striped64 implements Serializable {
34	private static final long serialVersionUID = 7249069246863182397L;
35
36	/**
37	* Version of max for use in retryUpdate
38	*/
39	final long fn(long v, long x) { return v > x ? v : x; }
40
41	/**
42	* Creates a new instance with initial maximum of {@code
43	* Long.MIN_VALUE}.
44	*/
45	public LongMaxUpdater() {
46	base = Long.MIN_VALUE;
47	}
48
49	/**
50	* Updates the maximum to be at least the given value.
51	*
52	* @param x the value to update
53	*/
54	public void update(long x) {
55	Cell[] as; long b, v; int[] hc; Cell a; int n;
56	if ((as = cells) != null \|\|
57	(b = base) < x && !casBase(b, x)) {
58	boolean uncontended = true;
59	if ((hc = threadHashCode.get()) == null \|\|
60	as == null \|\| (n = as.length) < 1 \|\|
61	(a = as[(n - 1) & hc[0]]) == null \|\|
62	((v = a.value) < x && !(uncontended = a.cas(v, x))))
63	retryUpdate(x, hc, uncontended);
64	}
65	}
66
67	/**
68	* Returns the current maximum. The returned value is
69	* <em>NOT</em> an atomic snapshot; invocation in the absence of
70	* concurrent updates returns an accurate result, but concurrent
71	* updates that occur while the value is being calculated might
72	* not be incorporated.
73	*
74	* @return the maximum
75	*/
76	public long max() {
77	Cell[] as = cells;
78	long max = base;
79	if (as != null) {
80	int n = as.length;
81	long v;
82	for (int i = 0; i < n; ++i) {
83	Cell a = as[i];
84	if (a != null && (v = a.value) > max)
85	max = v;
86	}
87	}
88	return max;
89	}
90
91	/**
92	* Resets variables maintaining updates to {@code Long.MIN_VALUE}.
93	* This method may be a useful alternative to creating a new
94	* updater, but is only effective if there are no concurrent
95	* updates. Because this method is intrinsically racy, it should
96	* only be used when it is known that no threads are concurrently
97	* updating.
98	*/
99	public void reset() {
100	internalReset(Long.MIN_VALUE);
101	}
102
103	/**
104	* Equivalent in effect to {@link #max} followed by {@link
105	* #reset}. This method may apply for example during quiescent
106	* points between multithreaded computations. If there are
107	* updates concurrent with this method, the returned value is
108	* <em>not</em> guaranteed to be the final value occurring before
109	* the reset.
110	*
111	* @return the maximum
112	*/
113	public long maxThenReset() {
114	Cell[] as = cells;
115	long max = base;
116	base = Long.MIN_VALUE;
117	if (as != null) {
118	int n = as.length;
119	for (int i = 0; i < n; ++i) {
120	Cell a = as[i];
121	if (a != null) {
122	long v = a.value;
123	a.value = Long.MIN_VALUE;
124	if (v > max)
125	max = v;
126	}
127	}
128	}
129	return max;
130	}
131
132	/**
133	* Returns the String representation of the {@link #max}.
134	* @return the String representation of the {@link #max}
135	*/
136	public String toString() {
137	return Long.toString(max());
138	}
139
140	/**
141	* Equivalent to {@link #max}.
142	*
143	* @return the maximum
144	*/
145	public long longValue() {
146	return max();
147	}
148
149	/**
150	* Returns the {@link #max} as an {@code int} after a narrowing
151	* primitive conversion.
152	*/
153	public int intValue() {
154	return (int)max();
155	}
156
157	/**
158	* Returns the {@link #max} as a {@code float}
159	* after a widening primitive conversion.
160	*/
161	public float floatValue() {
162	return (float)max();
163	}
164
165	/**
166	* Returns the {@link #max} as a {@code double} after a widening
167	* primitive conversion.
168	*/
169	public double doubleValue() {
170	return (double)max();
171	}
172
173	private void writeObject(ObjectOutputStream s) throws 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	}