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:	1.4
Committed:	Sun Nov 18 03:07:22 2012 UTC (11 years, 6 months ago) by jsr166
Branch:	MAIN
Changes since 1.3:	+1 -1 lines
Log Message:	properly close <em> javadoc tags
#	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.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	jsr166	1.4	* java.util.concurrent.atomic.</em>
28	dl	1.1	*
29	jsr166	1.2	* @since 1.8
30	dl	1.1	* @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	jsr166	1.3	* @return the String representation of the {@link #max}
134	dl	1.1	*/
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			}