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
#	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	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	}