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 java.util.concurrent; |
8 |
|
9 |
import java.util.Map; |
10 |
import java.util.Objects; |
11 |
import java.util.function.BiConsumer; |
12 |
import java.util.function.BiFunction; |
13 |
import java.util.function.Function; |
14 |
|
15 |
/** |
16 |
* A {@link java.util.Map} providing thread safety and atomicity |
17 |
* guarantees. |
18 |
* |
19 |
* <p>To maintain the specified guarantees, default implementations of |
20 |
* methods including {@link #putIfAbsent} inherited from {@link Map} |
21 |
* must be overridden by implementations of this interface. Similarly, |
22 |
* implementations of the collections returned by methods {@link |
23 |
* #keySet}, {@link #values}, and {@link #entrySet} must override |
24 |
* methods such as {@code removeIf} when necessary to |
25 |
* preserve atomicity guarantees. |
26 |
* |
27 |
* <p>Memory consistency effects: As with other concurrent |
28 |
* collections, actions in a thread prior to placing an object into a |
29 |
* {@code ConcurrentMap} as a key or value |
30 |
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
31 |
* actions subsequent to the access or removal of that object from |
32 |
* the {@code ConcurrentMap} in another thread. |
33 |
* |
34 |
* <p>This interface is a member of the |
35 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
36 |
* Java Collections Framework</a>. |
37 |
* |
38 |
* @since 1.5 |
39 |
* @author Doug Lea |
40 |
* @param <K> the type of keys maintained by this map |
41 |
* @param <V> the type of mapped values |
42 |
*/ |
43 |
public interface ConcurrentMap<K,V> extends Map<K,V> { |
44 |
|
45 |
/** |
46 |
* {@inheritDoc} |
47 |
* |
48 |
* @implNote This implementation assumes that the ConcurrentMap cannot |
49 |
* contain null values and {@code get()} returning null unambiguously means |
50 |
* the key is absent. Implementations which support null values |
51 |
* <strong>must</strong> override this default implementation. |
52 |
* |
53 |
* @throws ClassCastException {@inheritDoc} |
54 |
* @throws NullPointerException {@inheritDoc} |
55 |
* @since 1.8 |
56 |
*/ |
57 |
@Override |
58 |
default V getOrDefault(Object key, V defaultValue) { |
59 |
V v; |
60 |
return ((v = get(key)) != null) ? v : defaultValue; |
61 |
} |
62 |
|
63 |
/** |
64 |
* {@inheritDoc} |
65 |
* |
66 |
* @implSpec The default implementation is equivalent to, for this |
67 |
* {@code map}: |
68 |
* <pre> {@code |
69 |
* for (Map.Entry<K,V> entry : map.entrySet()) { |
70 |
* action.accept(entry.getKey(), entry.getValue()); |
71 |
* }}</pre> |
72 |
* |
73 |
* @implNote The default implementation assumes that |
74 |
* {@code IllegalStateException} thrown by {@code getKey()} or |
75 |
* {@code getValue()} indicates that the entry has been removed and cannot |
76 |
* be processed. Operation continues for subsequent entries. |
77 |
* |
78 |
* @throws NullPointerException {@inheritDoc} |
79 |
* @since 1.8 |
80 |
*/ |
81 |
@Override |
82 |
default void forEach(BiConsumer<? super K, ? super V> action) { |
83 |
Objects.requireNonNull(action); |
84 |
for (Map.Entry<K,V> entry : entrySet()) { |
85 |
K k; |
86 |
V v; |
87 |
try { |
88 |
k = entry.getKey(); |
89 |
v = entry.getValue(); |
90 |
} catch (IllegalStateException ise) { |
91 |
// this usually means the entry is no longer in the map. |
92 |
continue; |
93 |
} |
94 |
action.accept(k, v); |
95 |
} |
96 |
} |
97 |
|
98 |
/** |
99 |
* If the specified key is not already associated |
100 |
* with a value, associates it with the given value. |
101 |
* This is equivalent to, for this {@code map}: |
102 |
* <pre> {@code |
103 |
* if (!map.containsKey(key)) |
104 |
* return map.put(key, value); |
105 |
* else |
106 |
* return map.get(key);}</pre> |
107 |
* |
108 |
* except that the action is performed atomically. |
109 |
* |
110 |
* @implNote This implementation intentionally re-abstracts the |
111 |
* inappropriate default provided in {@code Map}. |
112 |
* |
113 |
* @param key key with which the specified value is to be associated |
114 |
* @param value value to be associated with the specified key |
115 |
* @return the previous value associated with the specified key, or |
116 |
* {@code null} if there was no mapping for the key. |
117 |
* (A {@code null} return can also indicate that the map |
118 |
* previously associated {@code null} with the key, |
119 |
* if the implementation supports null values.) |
120 |
* @throws UnsupportedOperationException if the {@code put} operation |
121 |
* is not supported by this map |
122 |
* @throws ClassCastException if the class of the specified key or value |
123 |
* prevents it from being stored in this map |
124 |
* @throws NullPointerException if the specified key or value is null, |
125 |
* and this map does not permit null keys or values |
126 |
* @throws IllegalArgumentException if some property of the specified key |
127 |
* or value prevents it from being stored in this map |
128 |
*/ |
129 |
V putIfAbsent(K key, V value); |
130 |
|
131 |
/** |
132 |
* Removes the entry for a key only if currently mapped to a given value. |
133 |
* This is equivalent to, for this {@code map}: |
134 |
* <pre> {@code |
135 |
* if (map.containsKey(key) |
136 |
* && Objects.equals(map.get(key), value)) { |
137 |
* map.remove(key); |
138 |
* return true; |
139 |
* } else { |
140 |
* return false; |
141 |
* }}</pre> |
142 |
* |
143 |
* except that the action is performed atomically. |
144 |
* |
145 |
* @implNote This implementation intentionally re-abstracts the |
146 |
* inappropriate default provided in {@code Map}. |
147 |
* |
148 |
* @param key key with which the specified value is associated |
149 |
* @param value value expected to be associated with the specified key |
150 |
* @return {@code true} if the value was removed |
151 |
* @throws UnsupportedOperationException if the {@code remove} operation |
152 |
* is not supported by this map |
153 |
* @throws ClassCastException if the key or value is of an inappropriate |
154 |
* type for this map |
155 |
* (<a href="../Collection.html#optional-restrictions">optional</a>) |
156 |
* @throws NullPointerException if the specified key or value is null, |
157 |
* and this map does not permit null keys or values |
158 |
* (<a href="../Collection.html#optional-restrictions">optional</a>) |
159 |
*/ |
160 |
boolean remove(Object key, Object value); |
161 |
|
162 |
/** |
163 |
* Replaces the entry for a key only if currently mapped to a given value. |
164 |
* This is equivalent to, for this {@code map}: |
165 |
* <pre> {@code |
166 |
* if (map.containsKey(key) |
167 |
* && Objects.equals(map.get(key), oldValue)) { |
168 |
* map.put(key, newValue); |
169 |
* return true; |
170 |
* } else { |
171 |
* return false; |
172 |
* }}</pre> |
173 |
* |
174 |
* except that the action is performed atomically. |
175 |
* |
176 |
* @implNote This implementation intentionally re-abstracts the |
177 |
* inappropriate default provided in {@code Map}. |
178 |
* |
179 |
* @param key key with which the specified value is associated |
180 |
* @param oldValue value expected to be associated with the specified key |
181 |
* @param newValue value to be associated with the specified key |
182 |
* @return {@code true} if the value was replaced |
183 |
* @throws UnsupportedOperationException if the {@code put} operation |
184 |
* is not supported by this map |
185 |
* @throws ClassCastException if the class of a specified key or value |
186 |
* prevents it from being stored in this map |
187 |
* @throws NullPointerException if a specified key or value is null, |
188 |
* and this map does not permit null keys or values |
189 |
* @throws IllegalArgumentException if some property of a specified key |
190 |
* or value prevents it from being stored in this map |
191 |
*/ |
192 |
boolean replace(K key, V oldValue, V newValue); |
193 |
|
194 |
/** |
195 |
* Replaces the entry for a key only if currently mapped to some value. |
196 |
* This is equivalent to, for this {@code map}: |
197 |
* <pre> {@code |
198 |
* if (map.containsKey(key)) { |
199 |
* return map.put(key, value); |
200 |
* } else { |
201 |
* return null; |
202 |
* }}</pre> |
203 |
* |
204 |
* except that the action is performed atomically. |
205 |
* |
206 |
* @implNote This implementation intentionally re-abstracts the |
207 |
* inappropriate default provided in {@code Map}. |
208 |
* |
209 |
* @param key key with which the specified value is associated |
210 |
* @param value value to be associated with the specified key |
211 |
* @return the previous value associated with the specified key, or |
212 |
* {@code null} if there was no mapping for the key. |
213 |
* (A {@code null} return can also indicate that the map |
214 |
* previously associated {@code null} with the key, |
215 |
* if the implementation supports null values.) |
216 |
* @throws UnsupportedOperationException if the {@code put} operation |
217 |
* is not supported by this map |
218 |
* @throws ClassCastException if the class of the specified key or value |
219 |
* prevents it from being stored in this map |
220 |
* @throws NullPointerException if the specified key or value is null, |
221 |
* and this map does not permit null keys or values |
222 |
* @throws IllegalArgumentException if some property of the specified key |
223 |
* or value prevents it from being stored in this map |
224 |
*/ |
225 |
V replace(K key, V value); |
226 |
|
227 |
/** |
228 |
* {@inheritDoc} |
229 |
* |
230 |
* @implSpec |
231 |
* <p>The default implementation is equivalent to, for this {@code map}: |
232 |
* <pre> {@code |
233 |
* for (Map.Entry<K,V> entry : map.entrySet()) { |
234 |
* do { |
235 |
* K k = entry.getKey(); |
236 |
* V v = entry.getValue(); |
237 |
* } while (!replace(k, v, function.apply(k, v))); |
238 |
* }}</pre> |
239 |
* |
240 |
* The default implementation may retry these steps when multiple |
241 |
* threads attempt updates including potentially calling the function |
242 |
* repeatedly for a given key. |
243 |
* |
244 |
* <p>This implementation assumes that the ConcurrentMap cannot contain null |
245 |
* values and {@code get()} returning null unambiguously means the key is |
246 |
* absent. Implementations which support null values <strong>must</strong> |
247 |
* override this default implementation. |
248 |
* |
249 |
* @throws UnsupportedOperationException {@inheritDoc} |
250 |
* @throws NullPointerException {@inheritDoc} |
251 |
* @throws ClassCastException {@inheritDoc} |
252 |
* @throws IllegalArgumentException {@inheritDoc} |
253 |
* @since 1.8 |
254 |
*/ |
255 |
@Override |
256 |
default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { |
257 |
Objects.requireNonNull(function); |
258 |
forEach((k,v) -> { |
259 |
while (!replace(k, v, function.apply(k, v))) { |
260 |
// v changed or k is gone |
261 |
if ( (v = get(k)) == null) { |
262 |
// k is no longer in the map. |
263 |
break; |
264 |
} |
265 |
} |
266 |
}); |
267 |
} |
268 |
|
269 |
/** |
270 |
* {@inheritDoc} |
271 |
* |
272 |
* @implSpec |
273 |
* The default implementation is equivalent to the following steps for this |
274 |
* {@code map}, then returning the current value or {@code null} if now |
275 |
* absent: |
276 |
* |
277 |
* <pre> {@code |
278 |
* if (map.get(key) == null) { |
279 |
* V newValue = mappingFunction.apply(key); |
280 |
* if (newValue != null) |
281 |
* return map.putIfAbsent(key, newValue); |
282 |
* }}</pre> |
283 |
* |
284 |
* The default implementation may retry these steps when multiple |
285 |
* threads attempt updates including potentially calling the mapping |
286 |
* function multiple times. |
287 |
* |
288 |
* <p>This implementation assumes that the ConcurrentMap cannot contain null |
289 |
* values and {@code get()} returning null unambiguously means the key is |
290 |
* absent. Implementations which support null values <strong>must</strong> |
291 |
* override this default implementation. |
292 |
* |
293 |
* @throws UnsupportedOperationException {@inheritDoc} |
294 |
* @throws ClassCastException {@inheritDoc} |
295 |
* @throws NullPointerException {@inheritDoc} |
296 |
* @since 1.8 |
297 |
*/ |
298 |
@Override |
299 |
default V computeIfAbsent(K key, |
300 |
Function<? super K, ? extends V> mappingFunction) { |
301 |
Objects.requireNonNull(mappingFunction); |
302 |
V v, newValue; |
303 |
return ((v = get(key)) == null && |
304 |
(newValue = mappingFunction.apply(key)) != null && |
305 |
(v = putIfAbsent(key, newValue)) == null) ? newValue : v; |
306 |
} |
307 |
|
308 |
/** |
309 |
* {@inheritDoc} |
310 |
* |
311 |
* @implSpec |
312 |
* The default implementation is equivalent to performing the following |
313 |
* steps for this {@code map}, then returning the current value or |
314 |
* {@code null} if now absent: |
315 |
* |
316 |
* <pre> {@code |
317 |
* if (map.get(key) != null) { |
318 |
* V oldValue = map.get(key); |
319 |
* V newValue = remappingFunction.apply(key, oldValue); |
320 |
* if (newValue != null) |
321 |
* map.replace(key, oldValue, newValue); |
322 |
* else |
323 |
* map.remove(key, oldValue); |
324 |
* }}</pre> |
325 |
* |
326 |
* The default implementation may retry these steps when multiple threads |
327 |
* attempt updates including potentially calling the remapping function |
328 |
* multiple times. |
329 |
* |
330 |
* <p>This implementation assumes that the ConcurrentMap cannot contain null |
331 |
* values and {@code get()} returning null unambiguously means the key is |
332 |
* absent. Implementations which support null values <strong>must</strong> |
333 |
* override this default implementation. |
334 |
* |
335 |
* @throws UnsupportedOperationException {@inheritDoc} |
336 |
* @throws ClassCastException {@inheritDoc} |
337 |
* @throws NullPointerException {@inheritDoc} |
338 |
* @since 1.8 |
339 |
*/ |
340 |
@Override |
341 |
default V computeIfPresent(K key, |
342 |
BiFunction<? super K, ? super V, ? extends V> remappingFunction) { |
343 |
Objects.requireNonNull(remappingFunction); |
344 |
V oldValue; |
345 |
while ((oldValue = get(key)) != null) { |
346 |
V newValue = remappingFunction.apply(key, oldValue); |
347 |
if (newValue != null) { |
348 |
if (replace(key, oldValue, newValue)) |
349 |
return newValue; |
350 |
} else if (remove(key, oldValue)) |
351 |
return null; |
352 |
} |
353 |
return oldValue; |
354 |
} |
355 |
|
356 |
/** |
357 |
* {@inheritDoc} |
358 |
* |
359 |
* @implSpec |
360 |
* The default implementation is equivalent to performing the following |
361 |
* steps for this {@code map}, then returning the current value or |
362 |
* {@code null} if absent: |
363 |
* |
364 |
* <pre> {@code |
365 |
* V oldValue = map.get(key); |
366 |
* V newValue = remappingFunction.apply(key, oldValue); |
367 |
* if (oldValue != null ) { |
368 |
* if (newValue != null) |
369 |
* map.replace(key, oldValue, newValue); |
370 |
* else |
371 |
* map.remove(key, oldValue); |
372 |
* } else { |
373 |
* if (newValue != null) |
374 |
* map.putIfAbsent(key, newValue); |
375 |
* else |
376 |
* return null; |
377 |
* }}</pre> |
378 |
* |
379 |
* The default implementation may retry these steps when multiple |
380 |
* threads attempt updates including potentially calling the remapping |
381 |
* function multiple times. |
382 |
* |
383 |
* <p>This implementation assumes that the ConcurrentMap cannot contain null |
384 |
* values and {@code get()} returning null unambiguously means the key is |
385 |
* absent. Implementations which support null values <strong>must</strong> |
386 |
* override this default implementation. |
387 |
* |
388 |
* @throws UnsupportedOperationException {@inheritDoc} |
389 |
* @throws ClassCastException {@inheritDoc} |
390 |
* @throws NullPointerException {@inheritDoc} |
391 |
* @since 1.8 |
392 |
*/ |
393 |
@Override |
394 |
default V compute(K key, |
395 |
BiFunction<? super K, ? super V, ? extends V> remappingFunction) { |
396 |
Objects.requireNonNull(remappingFunction); |
397 |
V oldValue = get(key); |
398 |
for (;;) { |
399 |
V newValue = remappingFunction.apply(key, oldValue); |
400 |
if (newValue == null) { |
401 |
// delete mapping |
402 |
if (oldValue != null || containsKey(key)) { |
403 |
// something to remove |
404 |
if (remove(key, oldValue)) { |
405 |
// removed the old value as expected |
406 |
return null; |
407 |
} |
408 |
|
409 |
// some other value replaced old value. try again. |
410 |
oldValue = get(key); |
411 |
} else { |
412 |
// nothing to do. Leave things as they were. |
413 |
return null; |
414 |
} |
415 |
} else { |
416 |
// add or replace old mapping |
417 |
if (oldValue != null) { |
418 |
// replace |
419 |
if (replace(key, oldValue, newValue)) { |
420 |
// replaced as expected. |
421 |
return newValue; |
422 |
} |
423 |
|
424 |
// some other value replaced old value. try again. |
425 |
oldValue = get(key); |
426 |
} else { |
427 |
// add (replace if oldValue was null) |
428 |
if ((oldValue = putIfAbsent(key, newValue)) == null) { |
429 |
// replaced |
430 |
return newValue; |
431 |
} |
432 |
|
433 |
// some other value replaced old value. try again. |
434 |
} |
435 |
} |
436 |
} |
437 |
} |
438 |
|
439 |
/** |
440 |
* {@inheritDoc} |
441 |
* |
442 |
* @implSpec |
443 |
* The default implementation is equivalent to performing the following |
444 |
* steps for this {@code map}, then returning the current value or |
445 |
* {@code null} if absent: |
446 |
* |
447 |
* <pre> {@code |
448 |
* V oldValue = map.get(key); |
449 |
* V newValue = (oldValue == null) ? value : |
450 |
* remappingFunction.apply(oldValue, value); |
451 |
* if (newValue == null) |
452 |
* map.remove(key); |
453 |
* else |
454 |
* map.put(key, newValue);}</pre> |
455 |
* |
456 |
* <p>The default implementation may retry these steps when multiple |
457 |
* threads attempt updates including potentially calling the remapping |
458 |
* function multiple times. |
459 |
* |
460 |
* <p>This implementation assumes that the ConcurrentMap cannot contain null |
461 |
* values and {@code get()} returning null unambiguously means the key is |
462 |
* absent. Implementations which support null values <strong>must</strong> |
463 |
* override this default implementation. |
464 |
* |
465 |
* @throws UnsupportedOperationException {@inheritDoc} |
466 |
* @throws ClassCastException {@inheritDoc} |
467 |
* @throws NullPointerException {@inheritDoc} |
468 |
* @since 1.8 |
469 |
*/ |
470 |
@Override |
471 |
default V merge(K key, V value, |
472 |
BiFunction<? super V, ? super V, ? extends V> remappingFunction) { |
473 |
Objects.requireNonNull(remappingFunction); |
474 |
Objects.requireNonNull(value); |
475 |
V oldValue = get(key); |
476 |
for (;;) { |
477 |
if (oldValue != null) { |
478 |
V newValue = remappingFunction.apply(oldValue, value); |
479 |
if (newValue != null) { |
480 |
if (replace(key, oldValue, newValue)) |
481 |
return newValue; |
482 |
} else if (remove(key, oldValue)) { |
483 |
return null; |
484 |
} |
485 |
oldValue = get(key); |
486 |
} else { |
487 |
if ((oldValue = putIfAbsent(key, value)) == null) { |
488 |
return value; |
489 |
} |
490 |
} |
491 |
} |
492 |
} |
493 |
} |