5 |
|
*/ |
6 |
|
|
7 |
|
package jsr166e; |
8 |
– |
import java.util.Arrays; |
8 |
|
import java.util.Random; |
9 |
|
import java.util.concurrent.atomic.AtomicInteger; |
10 |
|
import java.util.concurrent.atomic.AtomicLong; |
14 |
|
import java.io.ObjectOutputStream; |
15 |
|
|
16 |
|
/** |
17 |
< |
* A set of variables that together maintain a sum. When updates |
18 |
< |
* (method {@link #add}) are contended across threads, this set of |
19 |
< |
* adder variables may grow dynamically to reduce contention. Method |
21 |
< |
* {@link #sum} returns the current combined total across these |
22 |
< |
* adders. This value is <em>NOT</em> an atomic snapshot (concurrent |
23 |
< |
* updates may occur while the sum is being calculated), and so cannot |
24 |
< |
* be used alone for fine-grained synchronization control. |
17 |
> |
* One or more variables that together maintain an initially zero sum. |
18 |
> |
* When updates (method {@link #add}) are contended across threads, |
19 |
> |
* the set of variables may grow dynamically to reduce contention. |
20 |
|
* |
21 |
< |
* <p> This class may be applicable when many threads frequently |
22 |
< |
* update a common sum that is used for purposes such as collecting |
23 |
< |
* statistics. In this case, performance may be significantly faster |
24 |
< |
* than using a shared {@link AtomicLong}, at the expense of using |
25 |
< |
* much more space. On the other hand, if it is known that only one |
26 |
< |
* thread can ever update the sum, performance may be significantly |
27 |
< |
* slower than just updating a local variable. |
21 |
> |
* <p> This class is usually preferable to {@link AtomicLong} when |
22 |
> |
* multiple threads update a common sum that is used for purposes such |
23 |
> |
* as collecting statistics, not for fine-grained synchronization |
24 |
> |
* control. Under high update contention, throughput of this class is |
25 |
> |
* expected to be significantly higher, at the expense of higher space |
26 |
> |
* consumption. Under low contention, this class imposes very little |
27 |
> |
* time and space overhead compared to AtomicLong. On the other hand, |
28 |
> |
* in contexts where it is statically known that only one thread can |
29 |
> |
* ever update a sum, time and space overhead is noticeably greater |
30 |
> |
* than just updating a local variable. |
31 |
|
* |
32 |
< |
* <p>A StripedAdder may optionally be constructed with a given |
33 |
< |
* expected contention level; i.e., the number of threads that are |
34 |
< |
* expected to concurrently update the sum. Supplying an accurate |
35 |
< |
* value may improve performance by reducing the need for dynamic |
36 |
< |
* adjustment. |
32 |
> |
* <p> Method {@link #sum} returns the current combined total across |
33 |
> |
* the variables maintaining the sum. This value is <em>NOT</em> an |
34 |
> |
* atomic snapshot: Concurrent updates may occur while the sum is |
35 |
> |
* being calculated. However, updates cannot be "lost", so invocation |
36 |
> |
* of <code>sum</code> in the absence of concurrent updates always |
37 |
> |
* returns an accurate result. The sum may also be <code>reset</code> |
38 |
> |
* to zero, as an alternative to creating a new adder. However, |
39 |
> |
* method {@link #reset} is intrinsically racy, so should only be used |
40 |
> |
* when it is known that no threads are concurrently updating the sum. |
41 |
> |
* |
42 |
> |
* <p><em>jsr166e note: This class is targeted to be placed in |
43 |
> |
* java.util.concurrent.atomic<em> |
44 |
|
* |
45 |
|
* @author Doug Lea |
46 |
|
*/ |
48 |
|
private static final long serialVersionUID = 7249069246863182397L; |
49 |
|
|
50 |
|
/* |
51 |
< |
* A StripedAdder maintains a table of Atomic long variables. The |
52 |
< |
* table is indexed by per-thread hash codes. |
51 |
> |
* A StripedAdder maintains a lazily-initialized table of |
52 |
> |
* atomically updated variables, plus an extra "base" field. The |
53 |
> |
* table size is a power of two. Indexing uses masked per-thread |
54 |
> |
* hash codes |
55 |
|
* |
56 |
< |
* By default, the table is lazily initialized, to minimize |
57 |
< |
* footprint until adders are used. On first use, the table is set |
58 |
< |
* to size DEFAULT_INITIAL_SIZE (currently 8). Table size is |
59 |
< |
* bounded by the number of CPUS (if larger than the default |
60 |
< |
* size). |
56 |
> |
* Table entries are of class Cell; a variant of AtomicLong padded |
57 |
> |
* to reduce cache contention on most processors. Padding is |
58 |
> |
* overkill for most Atomics because they are usually irregularly |
59 |
> |
* scattered in memory and thus don't interfere much with each |
60 |
> |
* other. But Atomic objects residing in arrays will tend to be |
61 |
> |
* placed adjacent to each other, and so will most often share |
62 |
> |
* cache lines (with a huge negative performance impact) without |
63 |
> |
* this precaution. |
64 |
> |
* |
65 |
> |
* In part because Cells are relatively large, we avoid creating |
66 |
> |
* them until they are needed. When there is no contention, all |
67 |
> |
* updates are made to the base field. Upon first contention (a |
68 |
> |
* failed CAS on base update), the table is initialized to size 2. |
69 |
> |
* The table size is doubled upon further contention until |
70 |
> |
* reaching the nearest power of two greater than or equal to the |
71 |
> |
* number of CPUS. |
72 |
|
* |
73 |
|
* Per-thread hash codes are initialized to random values. |
74 |
< |
* Collisions are indicated by failed CASes when performing an add |
75 |
< |
* operation (see method retryAdd). Upon a collision, if the table |
76 |
< |
* size is less than the capacity, it is doubled in size unless |
77 |
< |
* some other thread holds lock. If a hashed slot is empty, and |
78 |
< |
* lock is available, a new Adder is created. Otherwise, if the |
79 |
< |
* slot exists, a CAS is tried. Retries proceed by "double |
80 |
< |
* hashing", using a secondary hash (Marsaglia XorShift) to try to |
81 |
< |
* find a free slot. |
74 |
> |
* Contention and/or table collisions are indicated by failed |
75 |
> |
* CASes when performing an add operation (see method |
76 |
> |
* retryAdd). Upon a collision, if the table size is less than the |
77 |
> |
* capacity, it is doubled in size unless some other thread holds |
78 |
> |
* the lock. If a hashed slot is empty, and lock is available, a |
79 |
> |
* new Cell is created. Otherwise, if the slot exists, a CAS is |
80 |
> |
* tried. Retries proceed by "double hashing", using a secondary |
81 |
> |
* hash (Marsaglia XorShift) to try to find a free slot. |
82 |
|
* |
83 |
|
* The table size is capped because, when there are more threads |
84 |
|
* than CPUs, supposing that each thread were bound to a CPU, |
85 |
|
* there would exist a perfect hash function mapping threads to |
86 |
|
* slots that eliminates collisions. When we reach capacity, we |
87 |
|
* search for this mapping by randomly varying the hash codes of |
88 |
< |
* colliding threads. Because search is random, and failures only |
89 |
< |
* become known via CAS failures, convergence will be slow, and |
90 |
< |
* because threads are typically not bound to CPUS forever, may |
91 |
< |
* not occur at all. However, despite these limitations, observed |
92 |
< |
* contention is typically low in these cases. |
88 |
> |
* colliding threads. Because search is random, and collisions |
89 |
> |
* only become known via CAS failures, convergence can be slow, |
90 |
> |
* and because threads are typically not bound to CPUS forever, |
91 |
> |
* may not occur at all. However, despite these limitations, |
92 |
> |
* observed contention rates are typically low in these cases. |
93 |
|
* |
94 |
< |
* Table entries are of class Adder; a form of AtomicLong padded |
95 |
< |
* to reduce cache contention on most processors. Padding is |
96 |
< |
* overkill for most Atomics because they are usually irregularly |
97 |
< |
* scattered in memory and thus don't interfere much with each |
98 |
< |
* other. But Atomic objects residing in arrays will tend to be |
99 |
< |
* placed adjacent to each other, and so will most often share |
100 |
< |
* cache lines without this precaution. Adders are by default |
101 |
< |
* constructed upon first use, which further improves per-thread |
102 |
< |
* locality and helps reduce footprint. |
94 |
> |
* A single spinlock is used for initializing and resizing the |
95 |
> |
* table, as well as populating slots with new Cells. There is no |
96 |
> |
* need for a blocking lock: Upon lock contention, threads try |
97 |
> |
* other slots (or the base) rather than blocking. During these |
98 |
> |
* retries, there is increased contention and reduced locality, |
99 |
> |
* which is still better than alternatives. |
100 |
> |
* |
101 |
> |
* It is possible for a Cell to become unused when threads that |
102 |
> |
* once hashed to it terminate, as well as in the case where |
103 |
> |
* doubling the table causes no thread to hash to it under |
104 |
> |
* expanded mask. We do not try to detect or remove such cells, |
105 |
> |
* under the assumption that for long-running adders, observed |
106 |
> |
* contention levels will recur, so the cells will eventually be |
107 |
> |
* needed again; and for short-lived ones, it does not matter. |
108 |
|
* |
86 |
– |
* A single spinlock is used for resizing the table as well as |
87 |
– |
* populating slots with new Adders. Upon lock contention, threads |
88 |
– |
* try other slots rather than blocking. After initialization, at |
89 |
– |
* least one slot exists, so retries will eventually find a |
90 |
– |
* candidate Adder. During these retries, there is increased |
91 |
– |
* contention and reduced locality, which is still better than |
92 |
– |
* alternatives. |
93 |
– |
*/ |
94 |
– |
|
95 |
– |
/** |
96 |
– |
* Padded version of AtomicLong |
109 |
|
*/ |
98 |
– |
static final class Adder extends AtomicLong { |
99 |
– |
long p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe; |
100 |
– |
Adder(long x) { super(x); } |
101 |
– |
} |
110 |
|
|
111 |
|
private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
112 |
|
|
113 |
|
/** |
114 |
< |
* Table bounds. DEFAULT_INITIAL_SIZE is the table size set upon |
115 |
< |
* first use under default constructor, and must be a power of |
116 |
< |
* two. There is not much point in making size a lot smaller than |
117 |
< |
* that of Adders though. CAP is the maximum allowed table size. |
118 |
< |
*/ |
119 |
< |
private static final int DEFAULT_INITIAL_SIZE = 8; |
120 |
< |
private static final int CAP = Math.max(NCPU, DEFAULT_INITIAL_SIZE); |
114 |
> |
* Padded variant of AtomicLong. The value field is placed |
115 |
> |
* between pads, hoping that the JVM doesn't reorder them. |
116 |
> |
* Updates are via inlined CAS in methods add and retryAdd. |
117 |
> |
*/ |
118 |
> |
static final class Cell { |
119 |
> |
volatile long p0, p1, p2, p3, p4, p5, p6; |
120 |
> |
volatile long value; |
121 |
> |
volatile long q0, q1, q2, q3, q4, q5, q6; |
122 |
> |
Cell(long x) { value = x; } |
123 |
> |
} |
124 |
|
|
125 |
|
/** |
126 |
|
* Holder for the thread-local hash code. The code is initially |
130 |
|
static final Random rng = new Random(); |
131 |
|
int code; |
132 |
|
HashCode() { |
133 |
< |
int h = rng.nextInt(); |
134 |
< |
code = (h == 0) ? 1 : h; // ensure nonzero |
133 |
> |
int h = rng.nextInt(); // Avoid zero to allow xorShift rehash |
134 |
> |
code = (h == 0) ? 1 : h; |
135 |
|
} |
136 |
|
} |
137 |
|
|
151 |
|
static final ThreadHashCode threadHashCode = new ThreadHashCode(); |
152 |
|
|
153 |
|
/** |
154 |
< |
* Common placeholder for empty arrays. |
154 |
> |
* Table of cells. When non-null, size is a power of 2. |
155 |
|
*/ |
156 |
< |
static final Adder[] EMPTY_ARRAY = new Adder[0]; |
156 |
> |
private transient volatile Cell[] cells; |
157 |
|
|
158 |
|
/** |
159 |
< |
* Table of adders. Size is either zero or a power of two, grows |
160 |
< |
* to be at most CAP. |
159 |
> |
* Base sum, used mainly when there is no contention, but also as |
160 |
> |
* a fallback during table initializion races. Updated via CAS. |
161 |
|
*/ |
162 |
< |
private transient volatile Adder[] adders; |
162 |
> |
private transient volatile long base; |
163 |
|
|
164 |
|
/** |
165 |
< |
* Serves as a lock when resizing and/or creating Adders. There |
155 |
< |
* is no need for a blocking lock: Except during initialization |
156 |
< |
* races, when busy, other threads try other slots. However, |
157 |
< |
* during (double-checked) initializations, we use the |
158 |
< |
* "synchronized" lock on this object. |
165 |
> |
* Spinlock (locked via CAS) used when resizing and/or creating Cells. |
166 |
|
*/ |
167 |
< |
private final AtomicInteger mutex; |
167 |
> |
private transient volatile int busy; |
168 |
|
|
169 |
|
/** |
170 |
< |
* Creates a new adder with zero sum. |
170 |
> |
* Creates a new adder with initial sum of zero. |
171 |
|
*/ |
172 |
|
public StripedAdder() { |
166 |
– |
this.adders = EMPTY_ARRAY; |
167 |
– |
this.mutex = new AtomicInteger(); |
168 |
– |
// remaining initialization on first call to add. |
169 |
– |
} |
170 |
– |
|
171 |
– |
/** |
172 |
– |
* Creates a new adder with zero sum, and with stripes presized |
173 |
– |
* for the given expected contention level. |
174 |
– |
* |
175 |
– |
* @param expectedContention the expected number of threads that |
176 |
– |
* will concurrently update the sum. |
177 |
– |
*/ |
178 |
– |
public StripedAdder(int expectedContention) { |
179 |
– |
if (expectedContention > 0) { |
180 |
– |
int cap = (expectedContention < CAP) ? expectedContention : CAP; |
181 |
– |
int size = 1; |
182 |
– |
while (size < cap) |
183 |
– |
size <<= 1; |
184 |
– |
Adder[] as = new Adder[size]; |
185 |
– |
for (int i = 0; i < size; ++i) |
186 |
– |
as[i] = new Adder(0); |
187 |
– |
this.adders = as; |
188 |
– |
} |
189 |
– |
else |
190 |
– |
this.adders = EMPTY_ARRAY; |
191 |
– |
this.mutex = new AtomicInteger(); |
173 |
|
} |
174 |
|
|
175 |
|
/** |
178 |
|
* @param x the value to add |
179 |
|
*/ |
180 |
|
public void add(long x) { |
181 |
< |
Adder[] as; Adder a; int n; long v; // locals to hold volatile reads |
182 |
< |
HashCode hc = threadHashCode.get(); |
183 |
< |
int h = hc.code; |
184 |
< |
if ((as = adders) == null || (n = as.length) < 1 || |
185 |
< |
(a = as[(n - 1) & h]) == null || |
186 |
< |
!a.compareAndSet(v = a.get(), v + x)) |
187 |
< |
retryAdd(x, hc); |
181 |
> |
Cell[] as; long v; HashCode hc; Cell a; int n; boolean contended; |
182 |
> |
if ((as = cells) != null || |
183 |
> |
!UNSAFE.compareAndSwapLong(this, baseOffset, v = base, v + x)) { |
184 |
> |
int h = (hc = threadHashCode.get()).code; |
185 |
> |
if (as != null && (n = as.length) > 0 && |
186 |
> |
(a = as[(n - 1) & h]) != null) { |
187 |
> |
if (UNSAFE.compareAndSwapLong(a, valueOffset, |
188 |
> |
v = a.value, v + x)) |
189 |
> |
return; |
190 |
> |
contended = true; |
191 |
> |
} |
192 |
> |
else |
193 |
> |
contended = false; |
194 |
> |
retryAdd(x, hc, contended); |
195 |
> |
} |
196 |
|
} |
197 |
|
|
198 |
|
/** |
199 |
|
* Handle cases of add involving initialization, resizing, |
200 |
< |
* creating new Adders, and/or contention. See above for |
201 |
< |
* explanation. |
200 |
> |
* creating new Cells, and/or contention. See above for |
201 |
> |
* explanation. This method suffers the usual non-modularity |
202 |
> |
* problems of optimistic retry code, relying on rechecked sets of |
203 |
> |
* reads. |
204 |
> |
* |
205 |
> |
* @param x the value to add |
206 |
> |
* @param hc the hash code holder |
207 |
> |
* @param precontended true if CAS failed before call |
208 |
|
*/ |
209 |
< |
private void retryAdd(long x, HashCode hc) { |
209 |
> |
private void retryAdd(long x, HashCode hc, boolean precontended) { |
210 |
|
int h = hc.code; |
211 |
< |
final AtomicInteger mutex = this.mutex; |
217 |
< |
int collisions = 1 - mutex.get(); // first guess: collides if not locked |
211 |
> |
boolean collide = false; // true if last slot nonempty |
212 |
|
for (;;) { |
213 |
< |
Adder[] as; Adder a; long v; int k, n; |
214 |
< |
while ((as = adders) == null || (n = as.length) < 1) { |
215 |
< |
synchronized(mutex) { // Try to initialize |
216 |
< |
if (adders == as) { |
217 |
< |
Adder[] rs = new Adder[DEFAULT_INITIAL_SIZE]; |
218 |
< |
rs[h & (DEFAULT_INITIAL_SIZE - 1)] = new Adder(0); |
219 |
< |
adders = rs; |
213 |
> |
Cell[] as; Cell a; int n; |
214 |
> |
if ((as = cells) != null && (n = as.length) > 0) { |
215 |
> |
if ((a = as[(n - 1) & h]) == null) { |
216 |
> |
if (busy == 0) { // Try to attach new Cell |
217 |
> |
Cell r = new Cell(x); // Optimistically create |
218 |
> |
if (busy == 0 && |
219 |
> |
UNSAFE.compareAndSwapInt(this, busyOffset, 0, 1)) { |
220 |
> |
boolean created = false; |
221 |
> |
try { // Recheck under lock |
222 |
> |
Cell[] rs; int m, j; |
223 |
> |
if ((rs = cells) != null && |
224 |
> |
(m = rs.length) > 0 && |
225 |
> |
rs[j = (m - 1) & h] == null) { |
226 |
> |
rs[j] = r; |
227 |
> |
created = true; |
228 |
> |
} |
229 |
> |
} finally { |
230 |
> |
busy = 0; |
231 |
> |
} |
232 |
> |
if (created) |
233 |
> |
break; |
234 |
> |
continue; // Slot is now non-empty |
235 |
> |
} |
236 |
|
} |
237 |
+ |
collide = false; |
238 |
|
} |
239 |
< |
collisions = 0; |
240 |
< |
} |
241 |
< |
|
242 |
< |
if ((a = as[k = (n - 1) & h]) == null) { // Try to add slot |
243 |
< |
if (mutex.get() == 0 && mutex.compareAndSet(0, 1)) { |
233 |
< |
try { |
234 |
< |
if (adders == as && as[k] == null) |
235 |
< |
a = as[k] = new Adder(x); |
236 |
< |
} finally { |
237 |
< |
mutex.set(0); |
238 |
< |
} |
239 |
< |
if (a != null) |
239 |
> |
else if (precontended) // CAS already known to fail |
240 |
> |
precontended = false; // Continue after rehash |
241 |
> |
else { |
242 |
> |
long v = a.value; |
243 |
> |
if (UNSAFE.compareAndSwapLong(a, valueOffset, v, v + x)) |
244 |
|
break; |
245 |
+ |
if (!collide) |
246 |
+ |
collide = true; |
247 |
+ |
else if (n >= NCPU || cells != as) |
248 |
+ |
collide = false; // Can't expand |
249 |
+ |
else if (busy == 0 && |
250 |
+ |
UNSAFE.compareAndSwapInt(this, busyOffset, 0, 1)) { |
251 |
+ |
collide = false; |
252 |
+ |
try { |
253 |
+ |
if (cells == as) { // Expand table |
254 |
+ |
Cell[] rs = new Cell[n << 1]; |
255 |
+ |
for (int i = 0; i < n; ++i) |
256 |
+ |
rs[i] = as[i]; |
257 |
+ |
cells = rs; |
258 |
+ |
} |
259 |
+ |
} finally { |
260 |
+ |
busy = 0; |
261 |
+ |
} |
262 |
+ |
continue; |
263 |
+ |
} |
264 |
|
} |
265 |
< |
collisions = 0; |
265 |
> |
h ^= h << 13; // Rehash |
266 |
> |
h ^= h >>> 17; |
267 |
> |
h ^= h << 5; |
268 |
|
} |
269 |
< |
else if (collisions != 0 && n < CAP && // Try to expand table |
270 |
< |
mutex.get() == 0 && mutex.compareAndSet(0, 1)) { |
271 |
< |
try { |
272 |
< |
if (adders == as) { |
273 |
< |
Adder[] rs = new Adder[n << 1]; |
274 |
< |
for (int i = 0; i < n; ++i) |
275 |
< |
rs[i] = as[i]; |
276 |
< |
adders = rs; |
269 |
> |
else if (busy == 0 && cells == as && |
270 |
> |
UNSAFE.compareAndSwapInt(this, busyOffset, 0, 1)) { |
271 |
> |
boolean init = false; |
272 |
> |
try { // Initialize |
273 |
> |
if (cells == as) { |
274 |
> |
Cell r = new Cell(x); |
275 |
> |
Cell[] rs = new Cell[2]; |
276 |
> |
rs[h & 1] = r; |
277 |
> |
cells = rs; |
278 |
> |
init = true; |
279 |
|
} |
280 |
|
} finally { |
281 |
< |
mutex.set(0); |
281 |
> |
busy = 0; |
282 |
|
} |
283 |
< |
collisions = 0; |
283 |
> |
if (init) |
284 |
> |
break; |
285 |
> |
} |
286 |
> |
else { // Lost initialization race |
287 |
> |
long b = base; // Fall back on using base |
288 |
> |
if (UNSAFE.compareAndSwapLong(this, baseOffset, b, b + x)) |
289 |
> |
break; |
290 |
|
} |
258 |
– |
else if (a.compareAndSet(v = a.get(), v + x)) |
259 |
– |
break; |
260 |
– |
else |
261 |
– |
collisions = 1; |
262 |
– |
h ^= h << 13; // Rehash |
263 |
– |
h ^= h >>> 17; |
264 |
– |
h ^= h << 5; |
291 |
|
} |
292 |
< |
hc.code = h; |
292 |
> |
hc.code = h; // Record index for next time |
293 |
|
} |
294 |
|
|
295 |
|
/** |
296 |
< |
* Returns an estimate of the current sum. The result is |
297 |
< |
* calculated by summing multiple variables, so may not be |
298 |
< |
* accurate if updates occur concurrently with this method. |
296 |
> |
* Equivalent to {@code add(1)}. |
297 |
> |
*/ |
298 |
> |
public void increment() { |
299 |
> |
add(1L); |
300 |
> |
} |
301 |
> |
|
302 |
> |
/** |
303 |
> |
* Equivalent to {@code add(-1)}. |
304 |
> |
*/ |
305 |
> |
public void decrement() { |
306 |
> |
add(-1L); |
307 |
> |
} |
308 |
> |
|
309 |
> |
/** |
310 |
> |
* Returns the current sum. The result is only guaranteed to be |
311 |
> |
* accurate in the absence of concurrent updates. Otherwise, it |
312 |
> |
* may fail to reflect one or more updates occuring while |
313 |
> |
* calculating the result. |
314 |
|
* |
315 |
< |
* @return the estimated sum |
315 |
> |
* @return the sum |
316 |
|
*/ |
317 |
|
public long sum() { |
318 |
< |
long sum = 0L; |
319 |
< |
Adder[] as = adders; |
318 |
> |
Cell[] as = cells; |
319 |
> |
long sum = base; |
320 |
|
if (as != null) { |
321 |
|
int n = as.length; |
322 |
|
for (int i = 0; i < n; ++i) { |
323 |
< |
Adder a = as[i]; |
323 |
> |
Cell a = as[i]; |
324 |
|
if (a != null) |
325 |
< |
sum += a.get(); |
325 |
> |
sum += a.value; |
326 |
|
} |
327 |
|
} |
328 |
|
return sum; |
329 |
|
} |
330 |
|
|
331 |
|
/** |
332 |
< |
* Resets each of the variables to zero. This is effective in |
333 |
< |
* fully resetting the sum only if there are no concurrent |
334 |
< |
* updates. |
332 |
> |
* Resets variables maintaining the sum to zero. This is |
333 |
> |
* effective in setting the sum to zero only if there are no |
334 |
> |
* concurrent updates. |
335 |
|
*/ |
336 |
|
public void reset() { |
337 |
< |
Adder[] as = adders; |
337 |
> |
Cell[] as = cells; |
338 |
> |
base = 0L; |
339 |
|
if (as != null) { |
340 |
|
int n = as.length; |
341 |
|
for (int i = 0; i < n; ++i) { |
342 |
< |
Adder a = as[i]; |
342 |
> |
Cell a = as[i]; |
343 |
|
if (a != null) |
344 |
< |
a.set(0L); |
344 |
> |
a.value = 0L; |
345 |
|
} |
346 |
|
} |
347 |
|
} |
348 |
|
|
349 |
|
/** |
350 |
< |
* Equivalent to {@code add(1)}. |
351 |
< |
*/ |
352 |
< |
public void increment() { |
353 |
< |
add(1L); |
354 |
< |
} |
355 |
< |
|
314 |
< |
/** |
315 |
< |
* Equivalent to {@code add(-1)}. |
316 |
< |
*/ |
317 |
< |
public void decrement() { |
318 |
< |
add(-1L); |
319 |
< |
} |
320 |
< |
|
321 |
< |
/** |
322 |
< |
* Equivalent to {@link #sum} followed by {@link #reset}. |
350 |
> |
* Equivalent in effect to {@link #sum} followed by {@link |
351 |
> |
* #reset}. This method may apply for example during quiescent |
352 |
> |
* points between multithreaded computations. If there are |
353 |
> |
* updates concurrent with this method, the returned value is |
354 |
> |
* <em>not</em> guaranteed to be the final sum occurring before |
355 |
> |
* the reset. |
356 |
|
* |
357 |
< |
* @return the estimated sum |
357 |
> |
* @return the sum |
358 |
|
*/ |
359 |
< |
public long sumAndReset() { |
360 |
< |
long sum = 0L; |
361 |
< |
Adder[] as = adders; |
359 |
> |
public long sumThenReset() { |
360 |
> |
Cell[] as = cells; |
361 |
> |
long sum = base; |
362 |
> |
base = 0L; |
363 |
|
if (as != null) { |
364 |
|
int n = as.length; |
365 |
|
for (int i = 0; i < n; ++i) { |
366 |
< |
Adder a = as[i]; |
366 |
> |
Cell a = as[i]; |
367 |
|
if (a != null) { |
368 |
< |
sum += a.get(); |
369 |
< |
a.set(0L); |
368 |
> |
sum += a.value; |
369 |
> |
a.value = 0L; |
370 |
|
} |
371 |
|
} |
372 |
|
} |
382 |
|
private void readObject(ObjectInputStream s) |
383 |
|
throws IOException, ClassNotFoundException { |
384 |
|
s.defaultReadObject(); |
385 |
< |
mutex.set(0); |
386 |
< |
add(s.readLong()); |
385 |
> |
busy = 0; |
386 |
> |
cells = null; |
387 |
> |
base = s.readLong(); |
388 |
> |
} |
389 |
> |
|
390 |
> |
// Unsafe mechanics |
391 |
> |
private static final sun.misc.Unsafe UNSAFE; |
392 |
> |
private static final long baseOffset; |
393 |
> |
private static final long busyOffset; |
394 |
> |
private static final long valueOffset; |
395 |
> |
static { |
396 |
> |
try { |
397 |
> |
UNSAFE = getUnsafe(); |
398 |
> |
Class<?> sk = StripedAdder.class; |
399 |
> |
baseOffset = UNSAFE.objectFieldOffset |
400 |
> |
(sk.getDeclaredField("base")); |
401 |
> |
busyOffset = UNSAFE.objectFieldOffset |
402 |
> |
(sk.getDeclaredField("busy")); |
403 |
> |
Class<?> ak = Cell.class; |
404 |
> |
valueOffset = UNSAFE.objectFieldOffset |
405 |
> |
(ak.getDeclaredField("value")); |
406 |
> |
} catch (Exception e) { |
407 |
> |
throw new Error(e); |
408 |
> |
} |
409 |
> |
} |
410 |
> |
|
411 |
> |
/** |
412 |
> |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
413 |
> |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
414 |
> |
* into a jdk. |
415 |
> |
* |
416 |
> |
* @return a sun.misc.Unsafe |
417 |
> |
*/ |
418 |
> |
private static sun.misc.Unsafe getUnsafe() { |
419 |
> |
try { |
420 |
> |
return sun.misc.Unsafe.getUnsafe(); |
421 |
> |
} catch (SecurityException se) { |
422 |
> |
try { |
423 |
> |
return java.security.AccessController.doPrivileged |
424 |
> |
(new java.security |
425 |
> |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
426 |
> |
public sun.misc.Unsafe run() throws Exception { |
427 |
> |
java.lang.reflect.Field f = sun.misc |
428 |
> |
.Unsafe.class.getDeclaredField("theUnsafe"); |
429 |
> |
f.setAccessible(true); |
430 |
> |
return (sun.misc.Unsafe) f.get(null); |
431 |
> |
}}); |
432 |
> |
} catch (java.security.PrivilegedActionException e) { |
433 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
434 |
> |
e.getCause()); |
435 |
> |
} |
436 |
> |
} |
437 |
|
} |
438 |
|
|
439 |
|
} |