| 6 |
|
|
| 7 |
|
package java.util.concurrent; |
| 8 |
|
import java.util.Map; |
| 9 |
+ |
import java.util.Objects; |
| 10 |
+ |
import java.util.function.BiConsumer; |
| 11 |
|
import java.util.function.BiFunction; |
| 12 |
+ |
import java.util.function.Function; |
| 13 |
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|
| 14 |
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/** |
| 15 |
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* A {@link java.util.Map} providing thread safety and atomicity |
| 16 |
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* guarantees. |
| 17 |
|
* |
| 18 |
+ |
* <p>To support atomic usages, ConcurrentMaps are expected not to |
| 19 |
+ |
* allow {@code null} as a legal value (and to throw exceptions upon |
| 20 |
+ |
* attempted insertions). This enables a return value of {@code null} |
| 21 |
+ |
* to unambiguously indicate the absence of a mapping. This interface |
| 22 |
+ |
* does not strictly forbid implementations that may hold {@code null} |
| 23 |
+ |
* values. However, in any that do so, a {@code null} value must bear |
| 24 |
+ |
* the same interpretation as the absence of a mapping in order to |
| 25 |
+ |
* conform to method atomicity requirements. Further, any that do so |
| 26 |
+ |
* must override all default method implementations. |
| 27 |
+ |
* |
| 28 |
+ |
* <p>Several methods (for example {@link #putIfAbsent}) inherited |
| 29 |
+ |
* from {@link Map} do not have default implementations, and so must |
| 30 |
+ |
* be provided by implementations of this interface, even though they |
| 31 |
+ |
* have (non-atomic) default implementations in the {@link Map} |
| 32 |
+ |
* interface. |
| 33 |
+ |
* |
| 34 |
|
* <p>Memory consistency effects: As with other concurrent |
| 35 |
|
* collections, actions in a thread prior to placing an object into a |
| 36 |
|
* {@code ConcurrentMap} as a key or value |
| 40 |
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* |
| 41 |
|
* <p>This interface is a member of the |
| 42 |
|
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 43 |
< |
* Java Collections Framework</a>. |
| 43 |
> |
* Java Caollections Framework</a>. |
| 44 |
|
* |
| 45 |
|
* @since 1.5 |
| 46 |
|
* @author Doug Lea |
| 47 |
|
* @param <K> the type of keys maintained by this map |
| 48 |
|
* @param <V> the type of mapped values |
| 49 |
|
*/ |
| 50 |
< |
public interface ConcurrentMap<K,V> extends Map<K,V> { |
| 50 |
> |
public interface ConcurrentMap<K, V> extends Map<K, V> { |
| 51 |
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|
| 52 |
|
/** |
| 53 |
|
* {@inheritDoc} |
| 54 |
|
* |
| 55 |
< |
* @implNote This implementation assumes that the ConcurrentMap cannot |
| 56 |
< |
* contain null values and get() returning null unambiguously means the key |
| 57 |
< |
* is absent. Implementations which support null values must override this |
| 58 |
< |
* default implementation. |
| 55 |
> |
* @implNote The default implementation returns the result of |
| 56 |
> |
* {@code get(key)} unless {@code null}, in which case it returns |
| 57 |
> |
* the given defaultValue. |
| 58 |
> |
* |
| 59 |
> |
* @throws ClassCastException {@inheritDoc} |
| 60 |
> |
* @throws NullPointerException {@inheritDoc} |
| 61 |
> |
* @since 1.8 |
| 62 |
|
*/ |
| 63 |
|
@Override |
| 64 |
|
default V getOrDefault(Object key, V defaultValue) { |
| 66 |
|
return ((v = get(key)) != null) ? v : defaultValue; |
| 67 |
|
} |
| 68 |
|
|
| 69 |
+ |
/** |
| 70 |
+ |
* {@inheritDoc} |
| 71 |
+ |
* |
| 72 |
+ |
* @implSpec The default implementation is equivalent to, for this |
| 73 |
+ |
* {@code map}: |
| 74 |
+ |
* <pre> {@code |
| 75 |
+ |
* for ((Map.Entry<K, V> entry : map.entrySet()) |
| 76 |
+ |
* action.accept(entry.getKey(), entry.getValue()); |
| 77 |
+ |
* }</pre> |
| 78 |
+ |
* |
| 79 |
+ |
* @implNote The default implementation assumes that {@code |
| 80 |
+ |
* IllegalStateException} thrown by {@code getKey()} or {@code |
| 81 |
+ |
* getValue()} indicates that the entry no longer exists. |
| 82 |
+ |
* Operation continues for subsequent entries. |
| 83 |
+ |
* |
| 84 |
+ |
* @throws NullPointerException {@inheritDoc} |
| 85 |
+ |
* @since 1.8 |
| 86 |
+ |
*/ |
| 87 |
+ |
@Override |
| 88 |
+ |
default void forEach(BiConsumer<? super K, ? super V> action) { |
| 89 |
+ |
Objects.requireNonNull(action); |
| 90 |
+ |
for (Map.Entry<K, V> entry : entrySet()) { |
| 91 |
+ |
K k; |
| 92 |
+ |
V v; |
| 93 |
+ |
try { |
| 94 |
+ |
k = entry.getKey(); |
| 95 |
+ |
v = entry.getValue(); |
| 96 |
+ |
} catch(IllegalStateException ise) { |
| 97 |
+ |
// this usually means the entry is no longer in the map. |
| 98 |
+ |
continue; |
| 99 |
+ |
} |
| 100 |
+ |
action.accept(k, v); |
| 101 |
+ |
} |
| 102 |
+ |
} |
| 103 |
+ |
|
| 104 |
|
/** |
| 105 |
|
* If the specified key is not already associated |
| 106 |
< |
* with a value, associate it with the given value. |
| 106 |
> |
* with a value, associates it with the given value. |
| 107 |
|
* This is equivalent to |
| 108 |
|
* <pre> {@code |
| 109 |
|
* if (!map.containsKey(key)) |
| 110 |
|
* return map.put(key, value); |
| 111 |
|
* else |
| 112 |
< |
* return map.get(key);}</pre> |
| 112 |
> |
* return map.get(key); |
| 113 |
> |
* }</pre> |
| 114 |
|
* |
| 115 |
|
* except that the action is performed atomically. |
| 116 |
|
* |
| 117 |
+ |
* @implNote There is no default implementation. |
| 118 |
+ |
* |
| 119 |
|
* @param key key with which the specified value is to be associated |
| 120 |
|
* @param value value to be associated with the specified key |
| 121 |
|
* @return the previous value associated with the specified key, or |
| 132 |
|
* @throws IllegalArgumentException if some property of the specified key |
| 133 |
|
* or value prevents it from being stored in this map |
| 134 |
|
*/ |
| 135 |
< |
V putIfAbsent(K key, V value); |
| 135 |
> |
V putIfAbsent(K key, V value); |
| 136 |
|
|
| 137 |
|
/** |
| 138 |
|
* Removes the entry for a key only if currently mapped to a given value. |
| 142 |
|
* map.remove(key); |
| 143 |
|
* return true; |
| 144 |
|
* } else |
| 145 |
< |
* return false;}</pre> |
| 145 |
> |
* return false; |
| 146 |
> |
* }</pre> |
| 147 |
|
* |
| 148 |
|
* except that the action is performed atomically. |
| 149 |
|
* |
| 150 |
+ |
* @implNote There is no default implementation. |
| 151 |
+ |
* |
| 152 |
|
* @param key key with which the specified value is associated |
| 153 |
|
* @param value value expected to be associated with the specified key |
| 154 |
|
* @return {@code true} if the value was removed |
| 171 |
|
* map.put(key, newValue); |
| 172 |
|
* return true; |
| 173 |
|
* } else |
| 174 |
< |
* return false;}</pre> |
| 174 |
> |
* return false; |
| 175 |
> |
* }</pre> |
| 176 |
|
* |
| 177 |
|
* except that the action is performed atomically. |
| 178 |
|
* |
| 179 |
+ |
* @implNote There is no default implementation. |
| 180 |
+ |
* |
| 181 |
|
* @param key key with which the specified value is associated |
| 182 |
|
* @param oldValue value expected to be associated with the specified key |
| 183 |
|
* @param newValue value to be associated with the specified key |
| 200 |
|
* if (map.containsKey(key)) { |
| 201 |
|
* return map.put(key, value); |
| 202 |
|
* } else |
| 203 |
< |
* return null;}</pre> |
| 203 |
> |
* return null; |
| 204 |
> |
* }</pre> |
| 205 |
|
* |
| 206 |
|
* except that the action is performed atomically. |
| 207 |
|
* |
| 208 |
+ |
* @implNote There is no default implementation. |
| 209 |
+ |
* |
| 210 |
|
* @param key key with which the specified value is associated |
| 211 |
|
* @param value value to be associated with the specified key |
| 212 |
|
* @return the previous value associated with the specified key, or |
| 228 |
|
/** |
| 229 |
|
* {@inheritDoc} |
| 230 |
|
* |
| 231 |
< |
* @implNote This implementation assumes that the ConcurrentMap cannot |
| 232 |
< |
* contain null values and get() returning null unambiguously means the key |
| 233 |
< |
* is absent. Implementations which support null values |
| 234 |
< |
* <strong>must</strong> override this default implementation. |
| 231 |
> |
* @implSpec |
| 232 |
> |
* <p>The default implementation is equivalent to, for this {@code map}: |
| 233 |
> |
* <pre> {@code |
| 234 |
> |
* for ((Map.Entry<K, V> entry : map.entrySet()) |
| 235 |
> |
* do { |
| 236 |
> |
* K k = entry.getKey(); |
| 237 |
> |
* V v = entry.getValue(); |
| 238 |
> |
* } while(!replace(k, v, function.apply(k, v))); |
| 239 |
> |
* }</pre> |
| 240 |
> |
* |
| 241 |
> |
* The default implementation may retry these steps when multiple |
| 242 |
> |
* threads attempt updates, and may call the function multiple |
| 243 |
> |
* times. |
| 244 |
> |
* |
| 245 |
> |
* @throws UnsupportedOperationException {@inheritDoc} |
| 246 |
> |
* @throws NullPointerException {@inheritDoc} |
| 247 |
> |
* @throws ClassCastException {@inheritDoc} |
| 248 |
> |
* @throws IllegalArgumentException {@inheritDoc} |
| 249 |
> |
* @since 1.8 |
| 250 |
|
*/ |
| 251 |
|
@Override |
| 252 |
|
default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { |
| 253 |
< |
if (function == null) throw new NullPointerException(); |
| 254 |
< |
for (Map.Entry<K,V> entry : entrySet()) { |
| 255 |
< |
K k; V v; |
| 256 |
< |
try { |
| 257 |
< |
k = entry.getKey(); |
| 258 |
< |
v = entry.getValue(); |
| 259 |
< |
} catch (IllegalStateException ise) { |
| 260 |
< |
continue; // skip if entry was removed |
| 253 |
> |
Objects.requireNonNull(function); |
| 254 |
> |
forEach((k,v) -> { |
| 255 |
> |
while(!replace(k, v, function.apply(k, v))) { |
| 256 |
> |
// v changed or k is gone |
| 257 |
> |
if ( (v = get(k)) == null) { |
| 258 |
> |
// k is no longer in the map. |
| 259 |
> |
break; |
| 260 |
> |
} |
| 261 |
|
} |
| 262 |
+ |
}); |
| 263 |
+ |
} |
| 264 |
|
|
| 265 |
< |
while (!replace(k, v, function.apply(k, v))) { |
| 266 |
< |
if ((v = get(k)) == null) // give up if k now removed |
| 267 |
< |
break; |
| 265 |
> |
/** |
| 266 |
> |
* {@inheritDoc} |
| 267 |
> |
* |
| 268 |
> |
* @implSpec |
| 269 |
> |
* The default implementation is equivalent to the following steps for this |
| 270 |
> |
* {@code map}, then returning the current value or {@code null} if now |
| 271 |
> |
* absent: |
| 272 |
> |
* |
| 273 |
> |
* <pre> {@code |
| 274 |
> |
* if (map.get(key) == null) { |
| 275 |
> |
* V newValue = mappingFunction.apply(key); |
| 276 |
> |
* if (newValue != null) |
| 277 |
> |
* return map.putIfAbsent(key, newValue); |
| 278 |
> |
* } |
| 279 |
> |
* }</pre> |
| 280 |
> |
* |
| 281 |
> |
* The default implementation may retry these steps when multiple |
| 282 |
> |
* threads attempt updates, and may call the mapping function |
| 283 |
> |
* multiple times. |
| 284 |
> |
* |
| 285 |
> |
* @throws UnsupportedOperationException {@inheritDoc} |
| 286 |
> |
* @throws ClassCastException {@inheritDoc} |
| 287 |
> |
* @throws NullPointerException {@inheritDoc} |
| 288 |
> |
* @since 1.8 |
| 289 |
> |
*/ |
| 290 |
> |
@Override |
| 291 |
> |
default V computeIfAbsent(K key, |
| 292 |
> |
Function<? super K, ? extends V> mappingFunction) { |
| 293 |
> |
Objects.requireNonNull(mappingFunction); |
| 294 |
> |
V v, newValue; |
| 295 |
> |
return ((v = get(key)) == null && |
| 296 |
> |
(newValue = mappingFunction.apply(key)) != null && |
| 297 |
> |
(v = putIfAbsent(key, newValue)) == null) ? newValue : v; |
| 298 |
> |
} |
| 299 |
> |
|
| 300 |
> |
/** |
| 301 |
> |
* {@inheritDoc} |
| 302 |
> |
* |
| 303 |
> |
* @implSpec |
| 304 |
> |
* The default implementation is equivalent to performing the following |
| 305 |
> |
* steps for this {@code map}, then returning the current value or |
| 306 |
> |
* {@code null} if now absent. : |
| 307 |
> |
* |
| 308 |
> |
* <pre> {@code |
| 309 |
> |
* if (map.get(key) != null) { |
| 310 |
> |
* V oldValue = map.get(key); |
| 311 |
> |
* V newValue = remappingFunction.apply(key, oldValue); |
| 312 |
> |
* if (newValue != null) |
| 313 |
> |
* map.replace(key, oldValue, newValue); |
| 314 |
> |
* else |
| 315 |
> |
* map.remove(key, oldValue); |
| 316 |
> |
* } |
| 317 |
> |
* }</pre> |
| 318 |
> |
* |
| 319 |
> |
* The default implementation may retry these steps when multiple |
| 320 |
> |
* threads attempt updates, and may call the remapping function |
| 321 |
> |
* multiple times. |
| 322 |
> |
* |
| 323 |
> |
* @throws UnsupportedOperationException {@inheritDoc} |
| 324 |
> |
* @throws ClassCastException {@inheritDoc} |
| 325 |
> |
* @throws NullPointerException {@inheritDoc} |
| 326 |
> |
* @since 1.8 |
| 327 |
> |
*/ |
| 328 |
> |
@Override |
| 329 |
> |
default V computeIfPresent(K key, |
| 330 |
> |
BiFunction<? super K, ? super V, ? extends V> remappingFunction) { |
| 331 |
> |
Objects.requireNonNull(remappingFunction); |
| 332 |
> |
V oldValue; |
| 333 |
> |
while((oldValue = get(key)) != null) { |
| 334 |
> |
V newValue = remappingFunction.apply(key, oldValue); |
| 335 |
> |
if (newValue != null) { |
| 336 |
> |
if (replace(key, oldValue, newValue)) |
| 337 |
> |
return newValue; |
| 338 |
> |
} else if (remove(key, oldValue)) |
| 339 |
> |
return null; |
| 340 |
> |
} |
| 341 |
> |
return oldValue; |
| 342 |
> |
} |
| 343 |
> |
|
| 344 |
> |
/** |
| 345 |
> |
* {@inheritDoc} |
| 346 |
> |
* |
| 347 |
> |
* @implSpec |
| 348 |
> |
* The default implementation is equivalent to performing the following |
| 349 |
> |
* steps for this {@code map}, then returning the current value or |
| 350 |
> |
* {@code null} if absent: |
| 351 |
> |
* |
| 352 |
> |
* <pre> {@code |
| 353 |
> |
* V oldValue = map.get(key); |
| 354 |
> |
* V newValue = remappingFunction.apply(key, oldValue); |
| 355 |
> |
* if (oldValue != null ) { |
| 356 |
> |
* if (newValue != null) |
| 357 |
> |
* map.replace(key, oldValue, newValue); |
| 358 |
> |
* else |
| 359 |
> |
* map.remove(key, oldValue); |
| 360 |
> |
* } else { |
| 361 |
> |
* if (newValue != null) |
| 362 |
> |
* map.putIfAbsent(key, newValue); |
| 363 |
> |
* else |
| 364 |
> |
* return null; |
| 365 |
> |
* } |
| 366 |
> |
* }</pre> |
| 367 |
> |
* |
| 368 |
> |
* The default implementation may retry these steps when multiple |
| 369 |
> |
* threads attempt updates, and may call the remapping function |
| 370 |
> |
* multiple times. |
| 371 |
> |
* |
| 372 |
> |
* @throws UnsupportedOperationException {@inheritDoc} |
| 373 |
> |
* @throws ClassCastException {@inheritDoc} |
| 374 |
> |
* @throws NullPointerException {@inheritDoc} |
| 375 |
> |
* @since 1.8 |
| 376 |
> |
*/ |
| 377 |
> |
@Override |
| 378 |
> |
default V compute(K key, |
| 379 |
> |
BiFunction<? super K, ? super V, ? extends V> remappingFunction) { |
| 380 |
> |
Objects.requireNonNull(remappingFunction); |
| 381 |
> |
V oldValue = get(key); |
| 382 |
> |
for(;;) { |
| 383 |
> |
V newValue = remappingFunction.apply(key, oldValue); |
| 384 |
> |
if (newValue == null) { |
| 385 |
> |
// delete mapping |
| 386 |
> |
if (oldValue != null || containsKey(key)) { |
| 387 |
> |
// something to remove |
| 388 |
> |
if (remove(key, oldValue)) { |
| 389 |
> |
// removed the old value as expected |
| 390 |
> |
return null; |
| 391 |
> |
} |
| 392 |
> |
|
| 393 |
> |
// some other value replaced old value. try again. |
| 394 |
> |
oldValue = get(key); |
| 395 |
> |
} else { |
| 396 |
> |
// nothing to do. Leave things as they were. |
| 397 |
> |
return null; |
| 398 |
> |
} |
| 399 |
> |
} else { |
| 400 |
> |
// add or replace old mapping |
| 401 |
> |
if (oldValue != null) { |
| 402 |
> |
// replace |
| 403 |
> |
if (replace(key, oldValue, newValue)) { |
| 404 |
> |
// replaced as expected. |
| 405 |
> |
return newValue; |
| 406 |
> |
} |
| 407 |
> |
|
| 408 |
> |
// some other value replaced old value. try again. |
| 409 |
> |
oldValue = get(key); |
| 410 |
> |
} else { |
| 411 |
> |
// add (replace if oldValue was null) |
| 412 |
> |
if ((oldValue = putIfAbsent(key, newValue)) == null) { |
| 413 |
> |
// replaced |
| 414 |
> |
return newValue; |
| 415 |
> |
} |
| 416 |
> |
|
| 417 |
> |
// some other value replaced old value. try again. |
| 418 |
> |
} |
| 419 |
|
} |
| 420 |
|
} |
| 421 |
|
} |
| 422 |
|
|
| 423 |
+ |
|
| 424 |
+ |
/** |
| 425 |
+ |
* {@inheritDoc} |
| 426 |
+ |
* |
| 427 |
+ |
* @implSpec |
| 428 |
+ |
* The default implementation is equivalent to performing the following |
| 429 |
+ |
* steps for this {@code map}, then returning the current value or |
| 430 |
+ |
* {@code null} if absent: |
| 431 |
+ |
* |
| 432 |
+ |
* <pre> {@code |
| 433 |
+ |
* V oldValue = map.get(key); |
| 434 |
+ |
* V newValue = (oldValue == null) ? value : |
| 435 |
+ |
* remappingFunction.apply(oldValue, value); |
| 436 |
+ |
* if (newValue == null) |
| 437 |
+ |
* map.remove(key); |
| 438 |
+ |
* else |
| 439 |
+ |
* map.put(key, newValue); |
| 440 |
+ |
* }</pre> |
| 441 |
+ |
* |
| 442 |
+ |
* The default implementation may retry these steps when multiple |
| 443 |
+ |
* threads attempt updates, and may call the remapping function |
| 444 |
+ |
* multiple times. |
| 445 |
+ |
* |
| 446 |
+ |
* @throws UnsupportedOperationException {@inheritDoc} |
| 447 |
+ |
* @throws ClassCastException {@inheritDoc} |
| 448 |
+ |
* @throws NullPointerException {@inheritDoc} |
| 449 |
+ |
* @since 1.8 |
| 450 |
+ |
*/ |
| 451 |
+ |
@Override |
| 452 |
+ |
default V merge(K key, V value, |
| 453 |
+ |
BiFunction<? super V, ? super V, ? extends V> remappingFunction) { |
| 454 |
+ |
Objects.requireNonNull(remappingFunction); |
| 455 |
+ |
Objects.requireNonNull(value); |
| 456 |
+ |
V oldValue = get(key); |
| 457 |
+ |
for (;;) { |
| 458 |
+ |
if (oldValue != null) { |
| 459 |
+ |
V newValue = remappingFunction.apply(oldValue, value); |
| 460 |
+ |
if (newValue != null) { |
| 461 |
+ |
if (replace(key, oldValue, newValue)) |
| 462 |
+ |
return newValue; |
| 463 |
+ |
} else if (remove(key, oldValue)) { |
| 464 |
+ |
return null; |
| 465 |
+ |
} |
| 466 |
+ |
oldValue = get(key); |
| 467 |
+ |
} else { |
| 468 |
+ |
if ((oldValue = putIfAbsent(key, value)) == null) { |
| 469 |
+ |
return value; |
| 470 |
+ |
} |
| 471 |
+ |
} |
| 472 |
+ |
} |
| 473 |
+ |
} |
| 474 |
|
} |
