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 (10 years 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
#	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	jsr166	1.17
9			import java.io.IOException;
10			import java.io.ObjectInputStream;
11			import java.io.ObjectOutputStream;
12			import java.io.Serializable;
13	dl	1.1	import java.util.concurrent.atomic.AtomicLong;
14
15			/**
16	dl	1.5	* 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	dl	1.1	*
23	jsr166	1.10	* <p>This class is usually preferable to {@link AtomicLong} when
24	dl	1.1	* 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	dl	1.5	* <p>This class extends {@link Number}, but does <em>not</em> define
32	jsr166	1.11	* 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	dl	1.1	*
36			* <p><em>jsr166e note: This class is targeted to be placed in
37	jsr166	1.9	* java.util.concurrent.atomic.</em>
38	dl	1.1	*
39	jsr166	1.7	* @since 1.8
40	dl	1.1	* @author Doug Lea
41			*/
42	dl	1.5	public class LongAdder extends Striped64 implements Serializable {
43	dl	1.1	private static final long serialVersionUID = 7249069246863182397L;
44
45			/**
46	dl	1.5	* Version of plus for use in retryUpdate
47	dl	1.1	*/
48	dl	1.5	final long fn(long v, long x) { return v + x; }
49	dl	1.1
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	dl	1.15	Cell[] as; long b, v; int[] hc; Cell a; int n;
63	dl	1.5	if ((as = cells) != null \|\| !casBase(b = base, b + x)) {
64	dl	1.1	boolean uncontended = true;
65	jsr166	1.16	if ((hc = threadHashCode.get()) == null \|\|
66	dl	1.15	as == null \|\| (n = as.length) < 1 \|\|
67			(a = as[(n - 1) & hc[0]]) == null \|\|
68	dl	1.5	!(uncontended = a.cas(v = a.value, v + x)))
69			retryUpdate(x, hc, uncontended);
70	dl	1.1	}
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	dl	1.5	* Returns the current sum. The returned value is <em>NOT</em> an
89	jsr166	1.14	* atomic snapshot; invocation in the absence of concurrent
90	dl	1.5	* updates returns an accurate result, but concurrent updates that
91			* occur while the sum is being calculated might not be
92			* incorporated.
93	dl	1.1	*
94			* @return the sum
95			*/
96			public long sum() {
97	dl	1.6	long sum = base;
98	dl	1.1	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	dl	1.5	* 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	dl	1.1	*/
117			public void reset() {
118	dl	1.5	internalReset(0L);
119	dl	1.1	}
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	dl	1.5	* <em>not</em> guaranteed to be the final value occurring before
127	dl	1.1	* the reset.
128			*
129			* @return the sum
130			*/
131			public long sumThenReset() {
132	dl	1.6	long sum = base;
133	dl	1.1	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	dl	1.6	sum += a.value;
141	dl	1.1	a.value = 0L;
142			}
143			}
144			}
145			return sum;
146			}
147
148	dl	1.5	/**
149			* Returns the String representation of the {@link #sum}.
150	jsr166	1.8	* @return the String representation of the {@link #sum}
151	dl	1.5	*/
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	jsr166	1.17	private void writeObject(ObjectOutputStream s) throws IOException {
190	dl	1.1	s.defaultWriteObject();
191			s.writeLong(sum());
192			}
193
194	jsr166	1.17	private void readObject(ObjectInputStream s)
195			throws IOException, ClassNotFoundException {
196	dl	1.1	s.defaultReadObject();
197			busy = 0;
198			cells = null;
199			base = s.readLong();
200			}
201
202			}