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 (10 years 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
#	User	Rev	Content
1	dl	1.1	/*
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	jsr166	1.11
9			import java.io.IOException;
10			import java.io.ObjectInputStream;
11			import java.io.ObjectOutputStream;
12	dl	1.1	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	jsr166	1.5	* 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	dl	1.1	*
27			* <p><em>jsr166e note: This class is targeted to be placed in
28	jsr166	1.4	* java.util.concurrent.atomic.</em>
29	dl	1.1	*
30	jsr166	1.2	* @since 1.8
31	dl	1.1	* @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	dl	1.9	Cell[] as; long b, v; int[] hc; Cell a; int n;
56	dl	1.1	if ((as = cells) != null \|\|
57			(b = base) < x && !casBase(b, x)) {
58			boolean uncontended = true;
59	jsr166	1.10	if ((hc = threadHashCode.get()) == null \|\|
60	dl	1.9	as == null \|\| (n = as.length) < 1 \|\|
61			(a = as[(n - 1) & hc[0]]) == null \|\|
62	dl	1.1	((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	jsr166	1.8	* <em>NOT</em> an atomic snapshot; invocation in the absence of
70	dl	1.1	* 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	jsr166	1.3	* @return the String representation of the {@link #max}
135	dl	1.1	*/
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	jsr166	1.11	private void writeObject(ObjectOutputStream s) throws IOException {
174	dl	1.1	s.defaultWriteObject();
175			s.writeLong(max());
176			}
177
178	jsr166	1.11	private void readObject(ObjectInputStream s)
179			throws IOException, ClassNotFoundException {
180	dl	1.1	s.defaultReadObject();
181			busy = 0;
182			cells = null;
183			base = s.readLong();
184			}
185
186			}