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.IOException; |
10 |
|
|
import java.io.Serializable; |
11 |
|
|
import java.io.ObjectInputStream; |
12 |
|
|
import java.io.ObjectOutputStream; |
13 |
|
|
|
14 |
|
|
/** |
15 |
dl |
1.5 |
* One or more variables that together maintain an initially zero |
16 |
|
|
* {@code long} sum. When updates (method {@link #add}) are contended |
17 |
|
|
* across threads, the set of variables may grow dynamically to reduce |
18 |
|
|
* contention. Method {@link #sum} (or, equivalently, {@link |
19 |
|
|
* #longValue}) returns the current total combined across the |
20 |
|
|
* variables maintaining the sum. |
21 |
dl |
1.1 |
* |
22 |
|
|
* <p> This class is usually preferable to {@link AtomicLong} when |
23 |
|
|
* multiple threads update a common sum that is used for purposes such |
24 |
|
|
* as collecting statistics, not for fine-grained synchronization |
25 |
|
|
* control. Under low update contention, the two classes have similar |
26 |
|
|
* characteristics. But under high contention, expected throughput of |
27 |
|
|
* this class is significantly higher, at the expense of higher space |
28 |
|
|
* consumption. |
29 |
|
|
* |
30 |
dl |
1.5 |
* <p>This class extends {@link Number}, but does <em>not</em> define |
31 |
|
|
* methods such as {@code hashCode} and {@code compareTo} because |
32 |
|
|
* instances are expected to be mutated, and so are not useful as |
33 |
|
|
* collection keys. |
34 |
dl |
1.1 |
* |
35 |
|
|
* <p><em>jsr166e note: This class is targeted to be placed in |
36 |
jsr166 |
1.9 |
* java.util.concurrent.atomic.</em> |
37 |
dl |
1.1 |
* |
38 |
jsr166 |
1.7 |
* @since 1.8 |
39 |
dl |
1.1 |
* @author Doug Lea |
40 |
|
|
*/ |
41 |
dl |
1.5 |
public class LongAdder extends Striped64 implements Serializable { |
42 |
dl |
1.1 |
private static final long serialVersionUID = 7249069246863182397L; |
43 |
|
|
|
44 |
|
|
/** |
45 |
dl |
1.5 |
* Version of plus for use in retryUpdate |
46 |
dl |
1.1 |
*/ |
47 |
dl |
1.5 |
final long fn(long v, long x) { return v + x; } |
48 |
dl |
1.1 |
|
49 |
|
|
/** |
50 |
|
|
* Creates a new adder with initial sum of zero. |
51 |
|
|
*/ |
52 |
|
|
public LongAdder() { |
53 |
|
|
} |
54 |
|
|
|
55 |
|
|
/** |
56 |
|
|
* Adds the given value. |
57 |
|
|
* |
58 |
|
|
* @param x the value to add |
59 |
|
|
*/ |
60 |
|
|
public void add(long x) { |
61 |
dl |
1.5 |
Cell[] as; long b, v; HashCode hc; Cell a; int n; |
62 |
|
|
if ((as = cells) != null || !casBase(b = base, b + x)) { |
63 |
dl |
1.1 |
boolean uncontended = true; |
64 |
|
|
int h = (hc = threadHashCode.get()).code; |
65 |
|
|
if (as == null || (n = as.length) < 1 || |
66 |
|
|
(a = as[(n - 1) & h]) == null || |
67 |
dl |
1.5 |
!(uncontended = a.cas(v = a.value, v + x))) |
68 |
|
|
retryUpdate(x, hc, uncontended); |
69 |
dl |
1.1 |
} |
70 |
|
|
} |
71 |
|
|
|
72 |
|
|
/** |
73 |
|
|
* Equivalent to {@code add(1)}. |
74 |
|
|
*/ |
75 |
|
|
public void increment() { |
76 |
|
|
add(1L); |
77 |
|
|
} |
78 |
|
|
|
79 |
|
|
/** |
80 |
|
|
* Equivalent to {@code add(-1)}. |
81 |
|
|
*/ |
82 |
|
|
public void decrement() { |
83 |
|
|
add(-1L); |
84 |
|
|
} |
85 |
|
|
|
86 |
|
|
/** |
87 |
dl |
1.5 |
* Returns the current sum. The returned value is <em>NOT</em> an |
88 |
|
|
* atomic snapshot: Invocation in the absence of concurrent |
89 |
|
|
* updates returns an accurate result, but concurrent updates that |
90 |
|
|
* occur while the sum is being calculated might not be |
91 |
|
|
* incorporated. |
92 |
dl |
1.1 |
* |
93 |
|
|
* @return the sum |
94 |
|
|
*/ |
95 |
|
|
public long sum() { |
96 |
dl |
1.6 |
long sum = base; |
97 |
dl |
1.1 |
Cell[] as = cells; |
98 |
|
|
if (as != null) { |
99 |
|
|
int n = as.length; |
100 |
|
|
for (int i = 0; i < n; ++i) { |
101 |
|
|
Cell a = as[i]; |
102 |
|
|
if (a != null) |
103 |
|
|
sum += a.value; |
104 |
|
|
} |
105 |
|
|
} |
106 |
|
|
return sum; |
107 |
|
|
} |
108 |
|
|
|
109 |
|
|
/** |
110 |
dl |
1.5 |
* Resets variables maintaining the sum to zero. This method may |
111 |
|
|
* be a useful alternative to creating a new adder, but is only |
112 |
|
|
* effective if there are no concurrent updates. Because this |
113 |
|
|
* method is intrinsically racy, it should only be used when it is |
114 |
|
|
* known that no threads are concurrently updating. |
115 |
dl |
1.1 |
*/ |
116 |
|
|
public void reset() { |
117 |
dl |
1.5 |
internalReset(0L); |
118 |
dl |
1.1 |
} |
119 |
|
|
|
120 |
|
|
/** |
121 |
|
|
* Equivalent in effect to {@link #sum} followed by {@link |
122 |
|
|
* #reset}. This method may apply for example during quiescent |
123 |
|
|
* points between multithreaded computations. If there are |
124 |
|
|
* updates concurrent with this method, the returned value is |
125 |
dl |
1.5 |
* <em>not</em> guaranteed to be the final value occurring before |
126 |
dl |
1.1 |
* the reset. |
127 |
|
|
* |
128 |
|
|
* @return the sum |
129 |
|
|
*/ |
130 |
|
|
public long sumThenReset() { |
131 |
dl |
1.6 |
long sum = base; |
132 |
dl |
1.1 |
Cell[] as = cells; |
133 |
|
|
base = 0L; |
134 |
|
|
if (as != null) { |
135 |
|
|
int n = as.length; |
136 |
|
|
for (int i = 0; i < n; ++i) { |
137 |
|
|
Cell a = as[i]; |
138 |
|
|
if (a != null) { |
139 |
dl |
1.6 |
sum += a.value; |
140 |
dl |
1.1 |
a.value = 0L; |
141 |
|
|
} |
142 |
|
|
} |
143 |
|
|
} |
144 |
|
|
return sum; |
145 |
|
|
} |
146 |
|
|
|
147 |
dl |
1.5 |
/** |
148 |
|
|
* Returns the String representation of the {@link #sum}. |
149 |
jsr166 |
1.8 |
* @return the String representation of the {@link #sum} |
150 |
dl |
1.5 |
*/ |
151 |
|
|
public String toString() { |
152 |
|
|
return Long.toString(sum()); |
153 |
|
|
} |
154 |
|
|
|
155 |
|
|
/** |
156 |
|
|
* Equivalent to {@link #sum}. |
157 |
|
|
* |
158 |
|
|
* @return the sum |
159 |
|
|
*/ |
160 |
|
|
public long longValue() { |
161 |
|
|
return sum(); |
162 |
|
|
} |
163 |
|
|
|
164 |
|
|
/** |
165 |
|
|
* Returns the {@link #sum} as an {@code int} after a narrowing |
166 |
|
|
* primitive conversion. |
167 |
|
|
*/ |
168 |
|
|
public int intValue() { |
169 |
|
|
return (int)sum(); |
170 |
|
|
} |
171 |
|
|
|
172 |
|
|
/** |
173 |
|
|
* Returns the {@link #sum} as a {@code float} |
174 |
|
|
* after a widening primitive conversion. |
175 |
|
|
*/ |
176 |
|
|
public float floatValue() { |
177 |
|
|
return (float)sum(); |
178 |
|
|
} |
179 |
|
|
|
180 |
|
|
/** |
181 |
|
|
* Returns the {@link #sum} as a {@code double} after a widening |
182 |
|
|
* primitive conversion. |
183 |
|
|
*/ |
184 |
|
|
public double doubleValue() { |
185 |
|
|
return (double)sum(); |
186 |
|
|
} |
187 |
|
|
|
188 |
dl |
1.1 |
private void writeObject(java.io.ObjectOutputStream s) |
189 |
|
|
throws java.io.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 |
|
|
} |