src/jsr166e/LongAdder.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;
import java.util.concurrent.atomic.AtomicLong;

/**
 * One or more variables that together maintain an initially zero
 * {@code long} sum.  When updates (method {@link #add}) are contended
 * across threads, the set of variables may grow dynamically to reduce
 * contention. Method {@link #sum} (or, equivalently, {@link
 * #longValue}) returns the current total combined across the
 * variables maintaining the sum.
 *
 * <p>This class is usually preferable to {@link AtomicLong} when
 * multiple threads update a common sum that is used for purposes such
 * as collecting statistics, not for fine-grained synchronization
 * control.  Under low update contention, the two classes have similar
 * characteristics. But under high contention, expected throughput of
 * this class is significantly higher, at the expense of higher space
 * consumption.
 *
 * <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 LongAdder extends Striped64 implements Serializable {
    private static final long serialVersionUID = 7249069246863182397L;

    /**
     * Version of plus for use in retryUpdate
     */
    final long fn(long v, long x) { return v + x; }

    /**
     * Creates a new adder with initial sum of zero.
     */
    public LongAdder() {
    }

    /**
     * Adds the given value.
     *
     * @param x the value to add
     */
    public void add(long x) {
        Cell[] as; long b, v; int[] hc; Cell a; int n;
        if ((as = cells) != null || !casBase(b = base, b + x)) {
            boolean uncontended = true;
            if ((hc = threadHashCode.get()) == null ||
                as == null || (n = as.length) < 1 ||
                (a = as[(n - 1) & hc[0]]) == null ||
                !(uncontended = a.cas(v = a.value, v + x)))
                retryUpdate(x, hc, uncontended);
        }
    }

    /**
     * Equivalent to {@code add(1)}.
     */
    public void increment() {
        add(1L);
    }

    /**
     * Equivalent to {@code add(-1)}.
     */
    public void decrement() {
        add(-1L);
    }

    /**
     * Returns the current sum.  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 sum is being calculated might not be
     * incorporated.
     *
     * @return the sum
     */
    public long sum() {
        long sum = base;
        Cell[] as = cells;
        if (as != null) {
            int n = as.length;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null)
                    sum += a.value;
            }
        }
        return sum;
    }

    /**
     * Resets variables maintaining the sum to zero.  This method may
     * be a useful alternative to creating a new adder, 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(0L);
    }

    /**
     * Equivalent in effect to {@link #sum} 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 sum
     */
    public long sumThenReset() {
        long sum = base;
        Cell[] as = cells;
        base = 0L;
        if (as != null) {
            int n = as.length;
            for (int i = 0; i < n; ++i) {
                Cell a = as[i];
                if (a != null) {
                    sum += a.value;
                    a.value = 0L;
                }
            }
        }
        return sum;
    }

    /**
     * Returns the String representation of the {@link #sum}.
     * @return the String representation of the {@link #sum}
     */
    public String toString() {
        return Long.toString(sum());
    }

    /**
     * Equivalent to {@link #sum}.
     *
     * @return the sum
     */
    public long longValue() {
        return sum();
    }

    /**
     * Returns the {@link #sum} as an {@code int} after a narrowing
     * primitive conversion.
     */
    public int intValue() {
        return (int)sum();
    }

    /**
     * Returns the {@link #sum} as a {@code float}
     * after a widening primitive conversion.
     */
    public float floatValue() {
        return (float)sum();
    }

    /**
     * Returns the {@link #sum} as a {@code double} after a widening
     * primitive conversion.
     */
    public double doubleValue() {
        return (double)sum();
    }

    private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        s.writeLong(sum());
    }

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

}
Revision:	1.17
Committed:	Mon May 5 20:20:15 2014 UTC (9 years, 11 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.16:	+8 -5 lines
Log Message:	import everything to reduce diffs with guava fork
#	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
9	import java.io.IOException;
10	import java.io.ObjectInputStream;
11	import java.io.ObjectOutputStream;
12	import java.io.Serializable;
13	import java.util.concurrent.atomic.AtomicLong;
14
15	/**
16	* One or more variables that together maintain an initially zero
17	* {@code long} sum. When updates (method {@link #add}) are contended
18	* across threads, the set of variables may grow dynamically to reduce
19	* contention. Method {@link #sum} (or, equivalently, {@link
20	* #longValue}) returns the current total combined across the
21	* variables maintaining the sum.
22	*
23	* <p>This class is usually preferable to {@link AtomicLong} when
24	* multiple threads update a common sum that is used for purposes such
25	* as collecting statistics, not for fine-grained synchronization
26	* control. Under low update contention, the two classes have similar
27	* characteristics. But under high contention, expected throughput of
28	* this class is significantly higher, at the expense of higher space
29	* consumption.
30	*
31	* <p>This class extends {@link Number}, but does <em>not</em> define
32	* methods such as {@code equals}, {@code hashCode} and {@code
33	* compareTo} because instances are expected to be mutated, and so are
34	* not useful as collection keys.
35	*
36	* <p><em>jsr166e note: This class is targeted to be placed in
37	* java.util.concurrent.atomic.</em>
38	*
39	* @since 1.8
40	* @author Doug Lea
41	*/
42	public class LongAdder extends Striped64 implements Serializable {
43	private static final long serialVersionUID = 7249069246863182397L;
44
45	/**
46	* Version of plus for use in retryUpdate
47	*/
48	final long fn(long v, long x) { return v + x; }
49
50	/**
51	* Creates a new adder with initial sum of zero.
52	*/
53	public LongAdder() {
54	}
55
56	/**
57	* Adds the given value.
58	*
59	* @param x the value to add
60	*/
61	public void add(long x) {
62	Cell[] as; long b, v; int[] hc; Cell a; int n;
63	if ((as = cells) != null \|\| !casBase(b = base, b + x)) {
64	boolean uncontended = true;
65	if ((hc = threadHashCode.get()) == null \|\|
66	as == null \|\| (n = as.length) < 1 \|\|
67	(a = as[(n - 1) & hc[0]]) == null \|\|
68	!(uncontended = a.cas(v = a.value, v + x)))
69	retryUpdate(x, hc, uncontended);
70	}
71	}
72
73	/**
74	* Equivalent to {@code add(1)}.
75	*/
76	public void increment() {
77	add(1L);
78	}
79
80	/**
81	* Equivalent to {@code add(-1)}.
82	*/
83	public void decrement() {
84	add(-1L);
85	}
86
87	/**
88	* Returns the current sum. The returned value is <em>NOT</em> an
89	* atomic snapshot; invocation in the absence of concurrent
90	* updates returns an accurate result, but concurrent updates that
91	* occur while the sum is being calculated might not be
92	* incorporated.
93	*
94	* @return the sum
95	*/
96	public long sum() {
97	long sum = base;
98	Cell[] as = cells;
99	if (as != null) {
100	int n = as.length;
101	for (int i = 0; i < n; ++i) {
102	Cell a = as[i];
103	if (a != null)
104	sum += a.value;
105	}
106	}
107	return sum;
108	}
109
110	/**
111	* Resets variables maintaining the sum to zero. This method may
112	* be a useful alternative to creating a new adder, but is only
113	* effective if there are no concurrent updates. Because this
114	* method is intrinsically racy, it should only be used when it is
115	* known that no threads are concurrently updating.
116	*/
117	public void reset() {
118	internalReset(0L);
119	}
120
121	/**
122	* Equivalent in effect to {@link #sum} followed by {@link
123	* #reset}. This method may apply for example during quiescent
124	* points between multithreaded computations. If there are
125	* updates concurrent with this method, the returned value is
126	* <em>not</em> guaranteed to be the final value occurring before
127	* the reset.
128	*
129	* @return the sum
130	*/
131	public long sumThenReset() {
132	long sum = base;
133	Cell[] as = cells;
134	base = 0L;
135	if (as != null) {
136	int n = as.length;
137	for (int i = 0; i < n; ++i) {
138	Cell a = as[i];
139	if (a != null) {
140	sum += a.value;
141	a.value = 0L;
142	}
143	}
144	}
145	return sum;
146	}
147
148	/**
149	* Returns the String representation of the {@link #sum}.
150	* @return the String representation of the {@link #sum}
151	*/
152	public String toString() {
153	return Long.toString(sum());
154	}
155
156	/**
157	* Equivalent to {@link #sum}.
158	*
159	* @return the sum
160	*/
161	public long longValue() {
162	return sum();
163	}
164
165	/**
166	* Returns the {@link #sum} as an {@code int} after a narrowing
167	* primitive conversion.
168	*/
169	public int intValue() {
170	return (int)sum();
171	}
172
173	/**
174	* Returns the {@link #sum} as a {@code float}
175	* after a widening primitive conversion.
176	*/
177	public float floatValue() {
178	return (float)sum();
179	}
180
181	/**
182	* Returns the {@link #sum} as a {@code double} after a widening
183	* primitive conversion.
184	*/
185	public double doubleValue() {
186	return (double)sum();
187	}
188
189	private void writeObject(ObjectOutputStream s) throws IOException {
190	s.defaultWriteObject();
191	s.writeLong(sum());
192	}
193
194	private void readObject(ObjectInputStream s)
195	throws IOException, ClassNotFoundException {
196	s.defaultReadObject();
197	busy = 0;
198	cells = null;
199	base = s.readLong();
200	}
201
202	}