/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.lang3.concurrent;
  
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  
  /**
   * <p>
   * An utility class providing functionality related to the {@code
   * java.util.concurrent} package.
   * </p>
   *
   * @since 3.0
   * @version $Id: ConcurrentUtils.java 1436770 2013-01-22 07:09:45Z ggregory $
   */
  public class ConcurrentUtils {
  
      /**
       * Private constructor so that no instances can be created. This class
       * contains only static utility methods.
       */
      private ConcurrentUtils() {
      }
  
      /**
       * Inspects the cause of the specified {@code ExecutionException} and
       * creates a {@code ConcurrentException} with the checked cause if
       * necessary. This method performs the following checks on the cause of the
       * passed in exception:
       * <ul>
       * <li>If the passed in exception is <b>null</b> or the cause is
       * <b>null</b>, this method returns <b>null</b>.</li>
       * <li>If the cause is a runtime exception, it is directly thrown.</li>
       * <li>If the cause is an error, it is directly thrown, too.</li>
       * <li>In any other case the cause is a checked exception. The method then
       * creates a {@link ConcurrentException}, initializes it with the cause, and
       * returns it.</li>
       * </ul>
       *
       * @param ex the exception to be processed
       * @return a {@code ConcurrentException} with the checked cause
       */
      public static ConcurrentException extractCause(final ExecutionException ex) {
          if (ex == null || ex.getCause() == null) {
              return null;
          }
  
          throwCause(ex);
          return new ConcurrentException(ex.getMessage(), ex.getCause());
      }
  
      /**
       * Inspects the cause of the specified {@code ExecutionException} and
       * creates a {@code ConcurrentRuntimeException} with the checked cause if
       * necessary. This method works exactly like
       * {@link #extractCause(ExecutionException)}. The only difference is that
       * the cause of the specified {@code ExecutionException} is extracted as a
       * runtime exception. This is an alternative for client code that does not
       * want to deal with checked exceptions.
       *
       * @param ex the exception to be processed
       * @return a {@code ConcurrentRuntimeException} with the checked cause
       */
      public static ConcurrentRuntimeException extractCauseUnchecked(
              final ExecutionException ex) {
          if (ex == null || ex.getCause() == null) {
              return null;
          }
  
          throwCause(ex);
          return new ConcurrentRuntimeException(ex.getMessage(), ex.getCause());
      }
  
      /**
       * Handles the specified {@code ExecutionException}. This method calls
       * {@link #extractCause(ExecutionException)} for obtaining the cause of the
       * exception - which might already cause an unchecked exception or an error
       * being thrown. If the cause is a checked exception however, it is wrapped
       * in a {@code ConcurrentException}, which is thrown. If the passed in
       * exception is <b>null</b> or has no cause, the method simply returns
       * without throwing an exception.
       *
      * @param ex the exception to be handled
      * @throws ConcurrentException if the cause of the {@code
      * ExecutionException} is a checked exception
      */
     public static void handleCause(final ExecutionException ex)
             throws ConcurrentException {
         final ConcurrentException cex = extractCause(ex);
 
         if (cex != null) {
             throw cex;
         }
     }
 
     /**
      * Handles the specified {@code ExecutionException} and transforms it into a
      * runtime exception. This method works exactly like
      * {@link #handleCause(ExecutionException)}, but instead of a
      * {@link ConcurrentException} it throws a
      * {@link ConcurrentRuntimeException}. This is an alternative for client
      * code that does not want to deal with checked exceptions.
      *
      * @param ex the exception to be handled
      * @throws ConcurrentRuntimeException if the cause of the {@code
      * ExecutionException} is a checked exception; this exception is then
      * wrapped in the thrown runtime exception
      */
     public static void handleCauseUnchecked(final ExecutionException ex) {
         final ConcurrentRuntimeException crex = extractCauseUnchecked(ex);
 
         if (crex != null) {
             throw crex;
         }
     }
 
     /**
      * Tests whether the specified {@code Throwable} is a checked exception. If
      * not, an exception is thrown.
      *
      * @param ex the {@code Throwable} to check
      * @return a flag whether the passed in exception is a checked exception
      * @throws IllegalArgumentException if the {@code Throwable} is not a
      * checked exception
      */
     static Throwable checkedException(final Throwable ex) {
         if (ex != null && !(ex instanceof RuntimeException)
                 && !(ex instanceof Error)) {
             return ex;
         } else {
             throw new IllegalArgumentException("Not a checked exception: " + ex);
         }
     }
 
     /**
      * Tests whether the cause of the specified {@code ExecutionException}
      * should be thrown and does it if necessary.
      *
      * @param ex the exception in question
      */
     private static void throwCause(final ExecutionException ex) {
         if (ex.getCause() instanceof RuntimeException) {
             throw (RuntimeException) ex.getCause();
         }
 
         if (ex.getCause() instanceof Error) {
             throw (Error) ex.getCause();
         }
     }
 
     //-----------------------------------------------------------------------
     /**
      * Invokes the specified {@code ConcurrentInitializer} and returns the
      * object produced by the initializer. This method just invokes the {@code
      * get()} method of the given {@code ConcurrentInitializer}. It is
      * <b>null</b>-safe: if the argument is <b>null</b>, result is also
      * <b>null</b>.
      *
      * @param <T> the type of the object produced by the initializer
      * @param initializer the {@code ConcurrentInitializer} to be invoked
      * @return the object managed by the {@code ConcurrentInitializer}
      * @throws ConcurrentException if the {@code ConcurrentInitializer} throws
      * an exception
      */
     public static <T> T initialize(final ConcurrentInitializer<T> initializer)
             throws ConcurrentException {
         return initializer != null ? initializer.get() : null;
     }
 
     /**
      * Invokes the specified {@code ConcurrentInitializer} and transforms
      * occurring exceptions to runtime exceptions. This method works like
      * {@link #initialize(ConcurrentInitializer)}, but if the {@code
      * ConcurrentInitializer} throws a {@link ConcurrentException}, it is
      * caught, and the cause is wrapped in a {@link ConcurrentRuntimeException}.
      * So client code does not have to deal with checked exceptions.
      *
      * @param <T> the type of the object produced by the initializer
      * @param initializer the {@code ConcurrentInitializer} to be invoked
      * @return the object managed by the {@code ConcurrentInitializer}
      * @throws ConcurrentRuntimeException if the initializer throws an exception
      */
     public static <T> T initializeUnchecked(final ConcurrentInitializer<T> initializer) {
         try {
             return initialize(initializer);
         } catch (final ConcurrentException cex) {
             throw new ConcurrentRuntimeException(cex.getCause());
         }
     }
 
     //-----------------------------------------------------------------------
     /**
      * <p>
      * Puts a value in the specified {@code ConcurrentMap} if the key is not yet
      * present. This method works similar to the {@code putIfAbsent()} method of
      * the {@code ConcurrentMap} interface, but the value returned is different.
      * Basically, this method is equivalent to the following code fragment:
      *
      * <pre>
      * if (!map.containsKey(key)) {
      *     map.put(key, value);
      *     return value;
      * } else {
      *     return map.get(key);
      * }
      * </pre>
      *
      * except that the action is performed atomically. So this method always
      * returns the value which is stored in the map.
      * </p>
      * <p>
      * This method is <b>null</b>-safe: It accepts a <b>null</b> map as input
      * without throwing an exception. In this case the return value is
      * <b>null</b>, too.
      * </p>
      *
      * @param <K> the type of the keys of the map
      * @param <V> the type of the values of the map
      * @param map the map to be modified
      * @param key the key of the value to be added
      * @param value the value to be added
      * @return the value stored in the map after this operation
      */
     public static <K, V> V putIfAbsent(final ConcurrentMap<K, V> map, final K key, final V value) {
         if (map == null) {
             return null;
         }
 
         final V result = map.putIfAbsent(key, value);
         return result != null ? result : value;
     }
 
     /**
      * Checks if a concurrent map contains a key and creates a corresponding
      * value if not. This method first checks the presence of the key in the
      * given map. If it is already contained, its value is returned. Otherwise
      * the {@code get()} method of the passed in {@link ConcurrentInitializer}
      * is called. With the resulting object
      * {@link #putIfAbsent(ConcurrentMap, Object, Object)} is called. This
      * handles the case that in the meantime another thread has added the key to
      * the map. Both the map and the initializer can be <b>null</b>; in this
      * case this method simply returns <b>null</b>.
      *
      * @param <K> the type of the keys of the map
      * @param <V> the type of the values of the map
      * @param map the map to be modified
      * @param key the key of the value to be added
      * @param init the {@link ConcurrentInitializer} for creating the value
      * @return the value stored in the map after this operation; this may or may
      * not be the object created by the {@link ConcurrentInitializer}
      * @throws ConcurrentException if the initializer throws an exception
      */
     public static <K, V> V createIfAbsent(final ConcurrentMap<K, V> map, final K key,
             final ConcurrentInitializer<V> init) throws ConcurrentException {
         if (map == null || init == null) {
             return null;
         }
 
         final V value = map.get(key);
         if (value == null) {
             return putIfAbsent(map, key, init.get());
         }
         return value;
     }
 
     /**
      * Checks if a concurrent map contains a key and creates a corresponding
      * value if not, suppressing checked exceptions. This method calls
      * {@code createIfAbsent()}. If a {@link ConcurrentException} is thrown, it
      * is caught and re-thrown as a {@link ConcurrentRuntimeException}.
      *
      * @param <K> the type of the keys of the map
      * @param <V> the type of the values of the map
      * @param map the map to be modified
      * @param key the key of the value to be added
      * @param init the {@link ConcurrentInitializer} for creating the value
      * @return the value stored in the map after this operation; this may or may
      * not be the object created by the {@link ConcurrentInitializer}
      * @throws ConcurrentRuntimeException if the initializer throws an exception
      */
     public static <K, V> V createIfAbsentUnchecked(final ConcurrentMap<K, V> map,
             final K key, final ConcurrentInitializer<V> init) {
         try {
             return createIfAbsent(map, key, init);
         } catch (final ConcurrentException cex) {
             throw new ConcurrentRuntimeException(cex.getCause());
         }
     }
 
     //-----------------------------------------------------------------------
     /**
      * <p>
      * Gets an implementation of <code>Future</code> that is immediately done
      * and returns the specified constant value.
      * </p>
      * <p>
      * This can be useful to return a simple constant immediately from the
      * concurrent processing, perhaps as part of avoiding nulls.
      * A constant future can also be useful in testing.
      * </p>
      *
      * @param <T> the type of the value used by this {@code Future} object
      * @param value  the constant value to return, may be null
      * @return an instance of Future that will return the value, never null
      */
     public static <T> Future<T> constantFuture(final T value) {
         return new ConstantFuture<T>(value);
     }
 
     /**
      * A specialized {@code Future} implementation which wraps a constant value.
      * @param <T> the type of the value wrapped by this class
      */
     static final class ConstantFuture<T> implements Future<T> {
         /** The constant value. */
         private final T value;
 
         /**
          * Creates a new instance of {@code ConstantFuture} and initializes it
          * with the constant value.
          *
          * @param value the value (may be <b>null</b>)
          */
         ConstantFuture(final T value) {
             this.value = value;
         }
 
         /**
          * {@inheritDoc} This implementation always returns <b>true</b> because
          * the constant object managed by this {@code Future} implementation is
          * always available.
          */
         @Override
         public boolean isDone() {
             return true;
         }
 
         /**
          * {@inheritDoc} This implementation just returns the constant value.
          */
         @Override
         public T get() {
             return value;
         }
 
         /**
          * {@inheritDoc} This implementation just returns the constant value; it
          * does not block, therefore the timeout has no meaning.
          */
         @Override
         public T get(final long timeout, final TimeUnit unit) {
             return value;
         }
 
         /**
          * {@inheritDoc} This implementation always returns <b>false</b>; there
          * is no background process which could be cancelled.
          */
         @Override
         public boolean isCancelled() {
             return false;
         }
 
         /**
          * {@inheritDoc} The cancel operation is not supported. This
          * implementation always returns <b>false</b>.
          */
         @Override
         public boolean cancel(final boolean mayInterruptIfRunning) {
             return false;
         }
     }
 
 }