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

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

}
Revision:	1.10
Committed:	Mon May 5 01:57:35 2014 UTC (10 years ago) by jsr166
Branch:	MAIN
Changes since 1.9:	+1 -1 lines
Log Message:	whitespace
#	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			import java.io.Serializable;
9
10			/**
11			* One or more variables that together maintain a running {@code long}
12			* maximum with initial value {@code Long.MIN_VALUE}. When updates
13			* (method {@link #update}) are contended across threads, the set of
14			* variables may grow dynamically to reduce contention. Method {@link
15			* #max} (or, equivalently, {@link #longValue}) returns the current
16			* maximum across the variables maintaining updates.
17			*
18			* <p>This class extends {@link Number}, but does <em>not</em> define
19	jsr166	1.5	* methods such as {@code equals}, {@code hashCode} and {@code
20			* compareTo} because instances are expected to be mutated, and so are
21			* not useful as collection keys.
22	dl	1.1	*
23			* <p><em>jsr166e note: This class is targeted to be placed in
24	jsr166	1.4	* java.util.concurrent.atomic.</em>
25	dl	1.1	*
26	jsr166	1.2	* @since 1.8
27	dl	1.1	* @author Doug Lea
28			*/
29			public class LongMaxUpdater extends Striped64 implements Serializable {
30			private static final long serialVersionUID = 7249069246863182397L;
31
32			/**
33			* Version of max for use in retryUpdate
34			*/
35			final long fn(long v, long x) { return v > x ? v : x; }
36
37			/**
38			* Creates a new instance with initial maximum of {@code
39			* Long.MIN_VALUE}.
40			*/
41			public LongMaxUpdater() {
42			base = Long.MIN_VALUE;
43			}
44
45			/**
46			* Updates the maximum to be at least the given value.
47			*
48			* @param x the value to update
49			*/
50			public void update(long x) {
51	dl	1.9	Cell[] as; long b, v; int[] hc; Cell a; int n;
52	dl	1.1	if ((as = cells) != null \|\|
53			(b = base) < x && !casBase(b, x)) {
54			boolean uncontended = true;
55	jsr166	1.10	if ((hc = threadHashCode.get()) == null \|\|
56	dl	1.9	as == null \|\| (n = as.length) < 1 \|\|
57			(a = as[(n - 1) & hc[0]]) == null \|\|
58	dl	1.1	((v = a.value) < x && !(uncontended = a.cas(v, x))))
59			retryUpdate(x, hc, uncontended);
60			}
61			}
62
63			/**
64			* Returns the current maximum. The returned value is
65	jsr166	1.8	* <em>NOT</em> an atomic snapshot; invocation in the absence of
66	dl	1.1	* concurrent updates returns an accurate result, but concurrent
67			* updates that occur while the value is being calculated might
68			* not be incorporated.
69			*
70			* @return the maximum
71			*/
72			public long max() {
73			Cell[] as = cells;
74			long max = base;
75			if (as != null) {
76			int n = as.length;
77			long v;
78			for (int i = 0; i < n; ++i) {
79			Cell a = as[i];
80			if (a != null && (v = a.value) > max)
81			max = v;
82			}
83			}
84			return max;
85			}
86
87			/**
88			* Resets variables maintaining updates to {@code Long.MIN_VALUE}.
89			* This method may be a useful alternative to creating a new
90			* updater, but is only effective if there are no concurrent
91			* updates. Because this method is intrinsically racy, it should
92			* only be used when it is known that no threads are concurrently
93			* updating.
94			*/
95			public void reset() {
96			internalReset(Long.MIN_VALUE);
97			}
98
99			/**
100			* Equivalent in effect to {@link #max} followed by {@link
101			* #reset}. This method may apply for example during quiescent
102			* points between multithreaded computations. If there are
103			* updates concurrent with this method, the returned value is
104			* <em>not</em> guaranteed to be the final value occurring before
105			* the reset.
106			*
107			* @return the maximum
108			*/
109			public long maxThenReset() {
110			Cell[] as = cells;
111			long max = base;
112			base = Long.MIN_VALUE;
113			if (as != null) {
114			int n = as.length;
115			for (int i = 0; i < n; ++i) {
116			Cell a = as[i];
117			if (a != null) {
118			long v = a.value;
119			a.value = Long.MIN_VALUE;
120			if (v > max)
121			max = v;
122			}
123			}
124			}
125			return max;
126			}
127
128			/**
129			* Returns the String representation of the {@link #max}.
130	jsr166	1.3	* @return the String representation of the {@link #max}
131	dl	1.1	*/
132			public String toString() {
133			return Long.toString(max());
134			}
135
136			/**
137			* Equivalent to {@link #max}.
138			*
139			* @return the maximum
140			*/
141			public long longValue() {
142			return max();
143			}
144
145			/**
146			* Returns the {@link #max} as an {@code int} after a narrowing
147			* primitive conversion.
148			*/
149			public int intValue() {
150			return (int)max();
151			}
152
153			/**
154			* Returns the {@link #max} as a {@code float}
155			* after a widening primitive conversion.
156			*/
157			public float floatValue() {
158			return (float)max();
159			}
160
161			/**
162			* Returns the {@link #max} as a {@code double} after a widening
163			* primitive conversion.
164			*/
165			public double doubleValue() {
166			return (double)max();
167			}
168
169			private void writeObject(java.io.ObjectOutputStream s)
170			throws java.io.IOException {
171			s.defaultWriteObject();
172			s.writeLong(max());
173			}
174
175	jsr166	1.7	private void readObject(java.io.ObjectInputStream s)
176			throws java.io.IOException, ClassNotFoundException {
177	dl	1.1	s.defaultReadObject();
178			busy = 0;
179			cells = null;
180			base = s.readLong();
181			}
182
183			}