001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.lang3.concurrent;
018
019 import java.util.concurrent.ConcurrentMap;
020 import java.util.concurrent.ExecutionException;
021 import java.util.concurrent.Future;
022 import java.util.concurrent.TimeUnit;
023
024 /**
025 * <p>
026 * An utility class providing functionality related to the {@code
027 * java.util.concurrent} package.
028 * </p>
029 *
030 * @since 3.0
031 * @version $Id: ConcurrentUtils.java 1088899 2011-04-05 05:31:27Z bayard $
032 */
033 public class ConcurrentUtils {
034
035 /**
036 * Private constructor so that no instances can be created. This class
037 * contains only static utility methods.
038 */
039 private ConcurrentUtils() {
040 }
041
042 /**
043 * Inspects the cause of the specified {@code ExecutionException} and
044 * creates a {@code ConcurrentException} with the checked cause if
045 * necessary. This method performs the following checks on the cause of the
046 * passed in exception:
047 * <ul>
048 * <li>If the passed in exception is <b>null</b> or the cause is
049 * <b>null</b>, this method returns <b>null</b>.</li>
050 * <li>If the cause is a runtime exception, it is directly thrown.</li>
051 * <li>If the cause is an error, it is directly thrown, too.</li>
052 * <li>In any other case the cause is a checked exception. The method then
053 * creates a {@link ConcurrentException}, initializes it with the cause, and
054 * returns it.</li>
055 * </ul>
056 *
057 * @param ex the exception to be processed
058 * @return a {@code ConcurrentException} with the checked cause
059 */
060 public static ConcurrentException extractCause(ExecutionException ex) {
061 if (ex == null || ex.getCause() == null) {
062 return null;
063 }
064
065 throwCause(ex);
066 return new ConcurrentException(ex.getMessage(), ex.getCause());
067 }
068
069 /**
070 * Inspects the cause of the specified {@code ExecutionException} and
071 * creates a {@code ConcurrentRuntimeException} with the checked cause if
072 * necessary. This method works exactly like
073 * {@link #extractCause(ExecutionException)}. The only difference is that
074 * the cause of the specified {@code ExecutionException} is extracted as a
075 * runtime exception. This is an alternative for client code that does not
076 * want to deal with checked exceptions.
077 *
078 * @param ex the exception to be processed
079 * @return a {@code ConcurrentRuntimeException} with the checked cause
080 */
081 public static ConcurrentRuntimeException extractCauseUnchecked(
082 ExecutionException ex) {
083 if (ex == null || ex.getCause() == null) {
084 return null;
085 }
086
087 throwCause(ex);
088 return new ConcurrentRuntimeException(ex.getMessage(), ex.getCause());
089 }
090
091 /**
092 * Handles the specified {@code ExecutionException}. This method calls
093 * {@link #extractCause(ExecutionException)} for obtaining the cause of the
094 * exception - which might already cause an unchecked exception or an error
095 * being thrown. If the cause is a checked exception however, it is wrapped
096 * in a {@code ConcurrentException}, which is thrown. If the passed in
097 * exception is <b>null</b> or has no cause, the method simply returns
098 * without throwing an exception.
099 *
100 * @param ex the exception to be handled
101 * @throws ConcurrentException if the cause of the {@code
102 * ExecutionException} is a checked exception
103 */
104 public static void handleCause(ExecutionException ex)
105 throws ConcurrentException {
106 ConcurrentException cex = extractCause(ex);
107
108 if (cex != null) {
109 throw cex;
110 }
111 }
112
113 /**
114 * Handles the specified {@code ExecutionException} and transforms it into a
115 * runtime exception. This method works exactly like
116 * {@link #handleCause(ExecutionException)}, but instead of a
117 * {@link ConcurrentException} it throws a
118 * {@link ConcurrentRuntimeException}. This is an alternative for client
119 * code that does not want to deal with checked exceptions.
120 *
121 * @param ex the exception to be handled
122 * @throws ConcurrentRuntimeException if the cause of the {@code
123 * ExecutionException} is a checked exception; this exception is then
124 * wrapped in the thrown runtime exception
125 */
126 public static void handleCauseUnchecked(ExecutionException ex) {
127 ConcurrentRuntimeException crex = extractCauseUnchecked(ex);
128
129 if (crex != null) {
130 throw crex;
131 }
132 }
133
134 /**
135 * Tests whether the specified {@code Throwable} is a checked exception. If
136 * not, an exception is thrown.
137 *
138 * @param ex the {@code Throwable} to check
139 * @return a flag whether the passed in exception is a checked exception
140 * @throws IllegalArgumentException if the {@code Throwable} is not a
141 * checked exception
142 */
143 static Throwable checkedException(Throwable ex) {
144 if (ex != null && !(ex instanceof RuntimeException)
145 && !(ex instanceof Error)) {
146 return ex;
147 } else {
148 throw new IllegalArgumentException("Not a checked exception: " + ex);
149 }
150 }
151
152 /**
153 * Tests whether the cause of the specified {@code ExecutionException}
154 * should be thrown and does it if necessary.
155 *
156 * @param ex the exception in question
157 */
158 private static void throwCause(ExecutionException ex) {
159 if (ex.getCause() instanceof RuntimeException) {
160 throw (RuntimeException) ex.getCause();
161 }
162
163 if (ex.getCause() instanceof Error) {
164 throw (Error) ex.getCause();
165 }
166 }
167
168 //-----------------------------------------------------------------------
169 /**
170 * Invokes the specified {@code ConcurrentInitializer} and returns the
171 * object produced by the initializer. This method just invokes the {@code
172 * get()} method of the given {@code ConcurrentInitializer}. It is
173 * <b>null</b>-safe: if the argument is <b>null</b>, result is also
174 * <b>null</b>.
175 *
176 * @param <T> the type of the object produced by the initializer
177 * @param initializer the {@code ConcurrentInitializer} to be invoked
178 * @return the object managed by the {@code ConcurrentInitializer}
179 * @throws ConcurrentException if the {@code ConcurrentInitializer} throws
180 * an exception
181 */
182 public static <T> T initialize(ConcurrentInitializer<T> initializer)
183 throws ConcurrentException {
184 return (initializer != null) ? initializer.get() : null;
185 }
186
187 /**
188 * Invokes the specified {@code ConcurrentInitializer} and transforms
189 * occurring exceptions to runtime exceptions. This method works like
190 * {@link #initialize(ConcurrentInitializer)}, but if the {@code
191 * ConcurrentInitializer} throws a {@link ConcurrentException}, it is
192 * caught, and the cause is wrapped in a {@link ConcurrentRuntimeException}.
193 * So client code does not have to deal with checked exceptions.
194 *
195 * @param <T> the type of the object produced by the initializer
196 * @param initializer the {@code ConcurrentInitializer} to be invoked
197 * @return the object managed by the {@code ConcurrentInitializer}
198 * @throws ConcurrentRuntimeException if the initializer throws an exception
199 */
200 public static <T> T initializeUnchecked(ConcurrentInitializer<T> initializer) {
201 try {
202 return initialize(initializer);
203 } catch (ConcurrentException cex) {
204 throw new ConcurrentRuntimeException(cex.getCause());
205 }
206 }
207
208 //-----------------------------------------------------------------------
209 /**
210 * <p>
211 * Puts a value in the specified {@code ConcurrentMap} if the key is not yet
212 * present. This method works similar to the {@code putIfAbsent()} method of
213 * the {@code ConcurrentMap} interface, but the value returned is different.
214 * Basically, this method is equivalent to the following code fragment:
215 *
216 * <pre>
217 * if (!map.containsKey(key)) {
218 * map.put(key, value);
219 * return value;
220 * } else {
221 * return map.get(key);
222 * }
223 * </pre>
224 *
225 * except that the action is performed atomically. So this method always
226 * returns the value which is stored in the map.
227 * </p>
228 * <p>
229 * This method is <b>null</b>-safe: It accepts a <b>null</b> map as input
230 * without throwing an exception. In this case the return value is
231 * <b>null</b>, too.
232 * </p>
233 *
234 * @param <K> the type of the keys of the map
235 * @param <V> the type of the values of the map
236 * @param map the map to be modified
237 * @param key the key of the value to be added
238 * @param value the value to be added
239 * @return the value stored in the map after this operation
240 */
241 public static <K, V> V putIfAbsent(ConcurrentMap<K, V> map, K key, V value) {
242 if (map == null) {
243 return null;
244 }
245
246 V result = map.putIfAbsent(key, value);
247 return (result != null) ? result : value;
248 }
249
250 /**
251 * Checks if a concurrent map contains a key and creates a corresponding
252 * value if not. This method first checks the presence of the key in the
253 * given map. If it is already contained, its value is returned. Otherwise
254 * the {@code get()} method of the passed in {@link ConcurrentInitializer}
255 * is called. With the resulting object
256 * {@link #putIfAbsent(ConcurrentMap, Object, Object)} is called. This
257 * handles the case that in the meantime another thread has added the key to
258 * the map. Both the map and the initializer can be <b>null</b>; in this
259 * case this method simply returns <b>null</b>.
260 *
261 * @param <K> the type of the keys of the map
262 * @param <V> the type of the values of the map
263 * @param map the map to be modified
264 * @param key the key of the value to be added
265 * @param init the {@link ConcurrentInitializer} for creating the value
266 * @return the value stored in the map after this operation; this may or may
267 * not be the object created by the {@link ConcurrentInitializer}
268 * @throws ConcurrentException if the initializer throws an exception
269 */
270 public static <K, V> V createIfAbsent(ConcurrentMap<K, V> map, K key,
271 ConcurrentInitializer<V> init) throws ConcurrentException {
272 if (map == null || init == null) {
273 return null;
274 }
275
276 V value = map.get(key);
277 if (value == null) {
278 return putIfAbsent(map, key, init.get());
279 }
280 return value;
281 }
282
283 /**
284 * Checks if a concurrent map contains a key and creates a corresponding
285 * value if not, suppressing checked exceptions. This method calls
286 * {@code createIfAbsent()}. If a {@link ConcurrentException} is thrown, it
287 * is caught and re-thrown as a {@link ConcurrentRuntimeException}.
288 *
289 * @param <K> the type of the keys of the map
290 * @param <V> the type of the values of the map
291 * @param map the map to be modified
292 * @param key the key of the value to be added
293 * @param init the {@link ConcurrentInitializer} for creating the value
294 * @return the value stored in the map after this operation; this may or may
295 * not be the object created by the {@link ConcurrentInitializer}
296 * @throws ConcurrentRuntimeException if the initializer throws an exception
297 */
298 public static <K, V> V createIfAbsentUnchecked(ConcurrentMap<K, V> map,
299 K key, ConcurrentInitializer<V> init) {
300 try {
301 return createIfAbsent(map, key, init);
302 } catch (ConcurrentException cex) {
303 throw new ConcurrentRuntimeException(cex.getCause());
304 }
305 }
306
307 //-----------------------------------------------------------------------
308 /**
309 * <p>
310 * Gets an implementation of <code>Future</code> that is immediately done
311 * and returns the specified constant value.
312 * </p>
313 * <p>
314 * This can be useful to return a simple constant immediately from the
315 * concurrent processing, perhaps as part of avoiding nulls.
316 * A constant future can also be useful in testing.
317 * </p>
318 *
319 * @param <T> the type of the value used by this {@code Future} object
320 * @param value the constant value to return, may be null
321 * @return an instance of Future that will return the value, never null
322 */
323 public static <T> Future<T> constantFuture(T value) {
324 return new ConstantFuture<T>(value);
325 }
326
327 /**
328 * A specialized {@code Future} implementation which wraps a constant value.
329 * @param <T> the type of the value wrapped by this class
330 */
331 static final class ConstantFuture<T> implements Future<T> {
332 /** The constant value. */
333 private final T value;
334
335 /**
336 * Creates a new instance of {@code ConstantFuture} and initializes it
337 * with the constant value.
338 *
339 * @param value the value (may be <b>null</b>)
340 */
341 ConstantFuture(T value) {
342 this.value = value;
343 }
344
345 /**
346 * {@inheritDoc} This implementation always returns <b>true</b> because
347 * the constant object managed by this {@code Future} implementation is
348 * always available.
349 */
350 public boolean isDone() {
351 return true;
352 }
353
354 /**
355 * {@inheritDoc} This implementation just returns the constant value.
356 */
357 public T get() {
358 return value;
359 }
360
361 /**
362 * {@inheritDoc} This implementation just returns the constant value; it
363 * does not block, therefore the timeout has no meaning.
364 */
365 public T get(long timeout, TimeUnit unit) {
366 return value;
367 }
368
369 /**
370 * {@inheritDoc} This implementation always returns <b>false</b>; there
371 * is no background process which could be cancelled.
372 */
373 public boolean isCancelled() {
374 return false;
375 }
376
377 /**
378 * {@inheritDoc} The cancel operation is not supported. This
379 * implementation always returns <b>false</b>.
380 */
381 public boolean cancel(boolean mayInterruptIfRunning) {
382 return false;
383 }
384 }
385
386 }