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 */
017package org.apache.commons.lang3.concurrent;
018
019import java.util.concurrent.ConcurrentMap;
020import java.util.concurrent.ExecutionException;
021import java.util.concurrent.Future;
022import 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 1436770 2013-01-22 07:09:45Z ggregory $
032 */
033public 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(final 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            final 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(final ExecutionException ex)
105            throws ConcurrentException {
106        final 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(final ExecutionException ex) {
127        final 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(final 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(final 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(final 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(final ConcurrentInitializer<T> initializer) {
201        try {
202            return initialize(initializer);
203        } catch (final 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(final ConcurrentMap<K, V> map, final K key, final V value) {
242        if (map == null) {
243            return null;
244        }
245
246        final 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(final ConcurrentMap<K, V> map, final K key,
271            final ConcurrentInitializer<V> init) throws ConcurrentException {
272        if (map == null || init == null) {
273            return null;
274        }
275
276        final 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(final ConcurrentMap<K, V> map,
299            final K key, final ConcurrentInitializer<V> init) {
300        try {
301            return createIfAbsent(map, key, init);
302        } catch (final 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(final 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(final 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        @Override
351        public boolean isDone() {
352            return true;
353        }
354
355        /**
356         * {@inheritDoc} This implementation just returns the constant value.
357         */
358        @Override
359        public T get() {
360            return value;
361        }
362
363        /**
364         * {@inheritDoc} This implementation just returns the constant value; it
365         * does not block, therefore the timeout has no meaning.
366         */
367        @Override
368        public T get(final long timeout, final TimeUnit unit) {
369            return value;
370        }
371
372        /**
373         * {@inheritDoc} This implementation always returns <b>false</b>; there
374         * is no background process which could be cancelled.
375         */
376        @Override
377        public boolean isCancelled() {
378            return false;
379        }
380
381        /**
382         * {@inheritDoc} The cancel operation is not supported. This
383         * implementation always returns <b>false</b>.
384         */
385        @Override
386        public boolean cancel(final boolean mayInterruptIfRunning) {
387            return false;
388        }
389    }
390
391}