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.util.concurrent.atomic.AtomicLong;
import java.io.Serializable;

/**
 * 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; HashCode hc; Cell a; int n;
        if ((as = cells) != null || !casBase(b = base, b + x)) {
            boolean uncontended = true;
            int h = (hc = threadHashCode.get()).code;
            if (as == null || (n = as.length) < 1 ||
                (a = as[(n - 1) & h]) == 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(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
        s.writeLong(sum());
    }

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

}
Revision:	1.14
Committed:	Mon Jan 14 02:02:41 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.13:	+1 -1 lines
Log Message:	punctuation
#	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.util.concurrent.atomic.AtomicLong;
9	import java.io.Serializable;
10
11	/**
12	* One or more variables that together maintain an initially zero
13	* {@code long} sum. When updates (method {@link #add}) are contended
14	* across threads, the set of variables may grow dynamically to reduce
15	* contention. Method {@link #sum} (or, equivalently, {@link
16	* #longValue}) returns the current total combined across the
17	* variables maintaining the sum.
18	*
19	* <p>This class is usually preferable to {@link AtomicLong} when
20	* multiple threads update a common sum that is used for purposes such
21	* as collecting statistics, not for fine-grained synchronization
22	* control. Under low update contention, the two classes have similar
23	* characteristics. But under high contention, expected throughput of
24	* this class is significantly higher, at the expense of higher space
25	* consumption.
26	*
27	* <p>This class extends {@link Number}, but does <em>not</em> define
28	* methods such as {@code equals}, {@code hashCode} and {@code
29	* compareTo} because instances are expected to be mutated, and so are
30	* not useful as collection keys.
31	*
32	* <p><em>jsr166e note: This class is targeted to be placed in
33	* java.util.concurrent.atomic.</em>
34	*
35	* @since 1.8
36	* @author Doug Lea
37	*/
38	public class LongAdder extends Striped64 implements Serializable {
39	private static final long serialVersionUID = 7249069246863182397L;
40
41	/**
42	* Version of plus for use in retryUpdate
43	*/
44	final long fn(long v, long x) { return v + x; }
45
46	/**
47	* Creates a new adder with initial sum of zero.
48	*/
49	public LongAdder() {
50	}
51
52	/**
53	* Adds the given value.
54	*
55	* @param x the value to add
56	*/
57	public void add(long x) {
58	Cell[] as; long b, v; HashCode hc; Cell a; int n;
59	if ((as = cells) != null \|\| !casBase(b = base, b + x)) {
60	boolean uncontended = true;
61	int h = (hc = threadHashCode.get()).code;
62	if (as == null \|\| (n = as.length) < 1 \|\|
63	(a = as[(n - 1) & h]) == null \|\|
64	!(uncontended = a.cas(v = a.value, v + x)))
65	retryUpdate(x, hc, uncontended);
66	}
67	}
68
69	/**
70	* Equivalent to {@code add(1)}.
71	*/
72	public void increment() {
73	add(1L);
74	}
75
76	/**
77	* Equivalent to {@code add(-1)}.
78	*/
79	public void decrement() {
80	add(-1L);
81	}
82
83	/**
84	* Returns the current sum. The returned value is <em>NOT</em> an
85	* atomic snapshot; invocation in the absence of concurrent
86	* updates returns an accurate result, but concurrent updates that
87	* occur while the sum is being calculated might not be
88	* incorporated.
89	*
90	* @return the sum
91	*/
92	public long sum() {
93	long sum = base;
94	Cell[] as = cells;
95	if (as != null) {
96	int n = as.length;
97	for (int i = 0; i < n; ++i) {
98	Cell a = as[i];
99	if (a != null)
100	sum += a.value;
101	}
102	}
103	return sum;
104	}
105
106	/**
107	* Resets variables maintaining the sum to zero. This method may
108	* be a useful alternative to creating a new adder, but is only
109	* effective if there are no concurrent updates. Because this
110	* method is intrinsically racy, it should only be used when it is
111	* known that no threads are concurrently updating.
112	*/
113	public void reset() {
114	internalReset(0L);
115	}
116
117	/**
118	* Equivalent in effect to {@link #sum} followed by {@link
119	* #reset}. This method may apply for example during quiescent
120	* points between multithreaded computations. If there are
121	* updates concurrent with this method, the returned value is
122	* <em>not</em> guaranteed to be the final value occurring before
123	* the reset.
124	*
125	* @return the sum
126	*/
127	public long sumThenReset() {
128	long sum = base;
129	Cell[] as = cells;
130	base = 0L;
131	if (as != null) {
132	int n = as.length;
133	for (int i = 0; i < n; ++i) {
134	Cell a = as[i];
135	if (a != null) {
136	sum += a.value;
137	a.value = 0L;
138	}
139	}
140	}
141	return sum;
142	}
143
144	/**
145	* Returns the String representation of the {@link #sum}.
146	* @return the String representation of the {@link #sum}
147	*/
148	public String toString() {
149	return Long.toString(sum());
150	}
151
152	/**
153	* Equivalent to {@link #sum}.
154	*
155	* @return the sum
156	*/
157	public long longValue() {
158	return sum();
159	}
160
161	/**
162	* Returns the {@link #sum} as an {@code int} after a narrowing
163	* primitive conversion.
164	*/
165	public int intValue() {
166	return (int)sum();
167	}
168
169	/**
170	* Returns the {@link #sum} as a {@code float}
171	* after a widening primitive conversion.
172	*/
173	public float floatValue() {
174	return (float)sum();
175	}
176
177	/**
178	* Returns the {@link #sum} as a {@code double} after a widening
179	* primitive conversion.
180	*/
181	public double doubleValue() {
182	return (double)sum();
183	}
184
185	private void writeObject(java.io.ObjectOutputStream s)
186	throws java.io.IOException {
187	s.defaultWriteObject();
188	s.writeLong(sum());
189	}
190
191	private void readObject(java.io.ObjectInputStream s)
192	throws java.io.IOException, ClassNotFoundException {
193	s.defaultReadObject();
194	busy = 0;
195	cells = null;
196	base = s.readLong();
197	}
198
199	}