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>
 *
 * @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:	1.1
Committed:	Tue Aug 2 18:04:12 2011 UTC (12 years, 9 months ago) by dl
Branch:	MAIN
Log Message:	Refactor and introduce new forms of update
#	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			* java.util.concurrent.atomic<em>
28			*
29			* @author Doug Lea
30			*/
31			public class LongMaxUpdater extends Striped64 implements Serializable {
32			private static final long serialVersionUID = 7249069246863182397L;
33
34			/**
35			* Version of max for use in retryUpdate
36			*/
37			final long fn(long v, long x) { return v > x ? v : x; }
38
39			/**
40			* Creates a new instance with initial maximum of {@code
41			* Long.MIN_VALUE}.
42			*/
43			public LongMaxUpdater() {
44			base = Long.MIN_VALUE;
45			}
46
47			/**
48			* Updates the maximum to be at least the given value.
49			*
50			* @param x the value to update
51			*/
52			public void update(long x) {
53			Cell[] as; long b, v; HashCode hc; Cell a; int n;
54			if ((as = cells) != null \|\|
55			(b = base) < x && !casBase(b, x)) {
56			boolean uncontended = true;
57			int h = (hc = threadHashCode.get()).code;
58			if (as == null \|\| (n = as.length) < 1 \|\|
59			(a = as[(n - 1) & h]) == null \|\|
60			((v = a.value) < x && !(uncontended = a.cas(v, x))))
61			retryUpdate(x, hc, uncontended);
62			}
63			}
64
65			/**
66			* Returns the current maximum. The returned value is
67			* <em>NOT</em> an atomic snapshot: Invocation in the absence of
68			* concurrent updates returns an accurate result, but concurrent
69			* updates that occur while the value is being calculated might
70			* not be incorporated.
71			*
72			* @return the maximum
73			*/
74			public long max() {
75			Cell[] as = cells;
76			long max = base;
77			if (as != null) {
78			int n = as.length;
79			long v;
80			for (int i = 0; i < n; ++i) {
81			Cell a = as[i];
82			if (a != null && (v = a.value) > max)
83			max = v;
84			}
85			}
86			return max;
87			}
88
89			/**
90			* Resets variables maintaining updates to {@code Long.MIN_VALUE}.
91			* This method may be a useful alternative to creating a new
92			* updater, but is only effective if there are no concurrent
93			* updates. Because this method is intrinsically racy, it should
94			* only be used when it is known that no threads are concurrently
95			* updating.
96			*/
97			public void reset() {
98			internalReset(Long.MIN_VALUE);
99			}
100
101			/**
102			* Equivalent in effect to {@link #max} followed by {@link
103			* #reset}. This method may apply for example during quiescent
104			* points between multithreaded computations. If there are
105			* updates concurrent with this method, the returned value is
106			* <em>not</em> guaranteed to be the final value occurring before
107			* the reset.
108			*
109			* @return the maximum
110			*/
111			public long maxThenReset() {
112			Cell[] as = cells;
113			long max = base;
114			base = Long.MIN_VALUE;
115			if (as != null) {
116			int n = as.length;
117			for (int i = 0; i < n; ++i) {
118			Cell a = as[i];
119			if (a != null) {
120			long v = a.value;
121			a.value = Long.MIN_VALUE;
122			if (v > max)
123			max = v;
124			}
125			}
126			}
127			return max;
128			}
129
130			/**
131			* Returns the String representation of the {@link #max}.
132			* @return the String representation of the {@link #max}.
133			*/
134			public String toString() {
135			return Long.toString(max());
136			}
137
138			/**
139			* Equivalent to {@link #max}.
140			*
141			* @return the maximum
142			*/
143			public long longValue() {
144			return max();
145			}
146
147			/**
148			* Returns the {@link #max} as an {@code int} after a narrowing
149			* primitive conversion.
150			*/
151			public int intValue() {
152			return (int)max();
153			}
154
155			/**
156			* Returns the {@link #max} as a {@code float}
157			* after a widening primitive conversion.
158			*/
159			public float floatValue() {
160			return (float)max();
161			}
162
163			/**
164			* Returns the {@link #max} as a {@code double} after a widening
165			* primitive conversion.
166			*/
167			public double doubleValue() {
168			return (double)max();
169			}
170
171			private void writeObject(java.io.ObjectOutputStream s)
172			throws java.io.IOException {
173			s.defaultWriteObject();
174			s.writeLong(max());
175			}
176
177			private void readObject(ObjectInputStream s)
178			throws IOException, ClassNotFoundException {
179			s.defaultReadObject();
180			busy = 0;
181			cells = null;
182			base = s.readLong();
183			}
184
185			}