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:	1.13
Committed:	Mon Jan 7 07:14:01 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.12:	+2 -5 lines
Log Message:	consistent style for readObject
#	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.util.concurrent.atomic.AtomicLong;
9			import java.io.Serializable;
10
11			/**
12	dl	1.5	* 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	dl	1.1	*
19	jsr166	1.10	* <p>This class is usually preferable to {@link AtomicLong} when
20	dl	1.1	* 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	dl	1.5	* <p>This class extends {@link Number}, but does <em>not</em> define
28	jsr166	1.11	* 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	dl	1.1	*
32			* <p><em>jsr166e note: This class is targeted to be placed in
33	jsr166	1.9	* java.util.concurrent.atomic.</em>
34	dl	1.1	*
35	jsr166	1.7	* @since 1.8
36	dl	1.1	* @author Doug Lea
37			*/
38	dl	1.5	public class LongAdder extends Striped64 implements Serializable {
39	dl	1.1	private static final long serialVersionUID = 7249069246863182397L;
40
41			/**
42	dl	1.5	* Version of plus for use in retryUpdate
43	dl	1.1	*/
44	dl	1.5	final long fn(long v, long x) { return v + x; }
45	dl	1.1
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	dl	1.5	Cell[] as; long b, v; HashCode hc; Cell a; int n;
59			if ((as = cells) != null \|\| !casBase(b = base, b + x)) {
60	dl	1.1	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	dl	1.5	!(uncontended = a.cas(v = a.value, v + x)))
65			retryUpdate(x, hc, uncontended);
66	dl	1.1	}
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	dl	1.5	* Returns the current sum. The returned value is <em>NOT</em> an
85	jsr166	1.12	* atomic snapshot: invocation in the absence of concurrent
86	dl	1.5	* updates returns an accurate result, but concurrent updates that
87			* occur while the sum is being calculated might not be
88			* incorporated.
89	dl	1.1	*
90			* @return the sum
91			*/
92			public long sum() {
93	dl	1.6	long sum = base;
94	dl	1.1	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	dl	1.5	* 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	dl	1.1	*/
113			public void reset() {
114	dl	1.5	internalReset(0L);
115	dl	1.1	}
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	dl	1.5	* <em>not</em> guaranteed to be the final value occurring before
123	dl	1.1	* the reset.
124			*
125			* @return the sum
126			*/
127			public long sumThenReset() {
128	dl	1.6	long sum = base;
129	dl	1.1	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	dl	1.6	sum += a.value;
137	dl	1.1	a.value = 0L;
138			}
139			}
140			}
141			return sum;
142			}
143
144	dl	1.5	/**
145			* Returns the String representation of the {@link #sum}.
146	jsr166	1.8	* @return the String representation of the {@link #sum}
147	dl	1.5	*/
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	dl	1.1	private void writeObject(java.io.ObjectOutputStream s)
186			throws java.io.IOException {
187			s.defaultWriteObject();
188			s.writeLong(sum());
189			}
190
191	jsr166	1.13	private void readObject(java.io.ObjectInputStream s)
192			throws java.io.IOException, ClassNotFoundException {
193	dl	1.1	s.defaultReadObject();
194			busy = 0;
195			cells = null;
196			base = s.readLong();
197			}
198
199			}