Coverage Report - org.apache.commons.lang3.concurrent.MultiBackgroundInitializer
 
Classes in this File Line Coverage Branch Coverage Complexity
MultiBackgroundInitializer
100%
39/39
100%
14/14
2
MultiBackgroundInitializer$1
N/A
N/A
2
MultiBackgroundInitializer$MultiBackgroundInitializerResults
100%
19/19
100%
2/2
2
 
 1  
 /*
 2  
  * Licensed to the Apache Software Foundation (ASF) under one or more
 3  
  * contributor license agreements.  See the NOTICE file distributed with
 4  
  * this work for additional information regarding copyright ownership.
 5  
  * The ASF licenses this file to You under the Apache License, Version 2.0
 6  
  * (the "License"); you may not use this file except in compliance with
 7  
  * the License.  You may obtain a copy of the License at
 8  
  *
 9  
  *      http://www.apache.org/licenses/LICENSE-2.0
 10  
  *
 11  
  * Unless required by applicable law or agreed to in writing, software
 12  
  * distributed under the License is distributed on an "AS IS" BASIS,
 13  
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 14  
  * See the License for the specific language governing permissions and
 15  
  * limitations under the License.
 16  
  */
 17  
 package org.apache.commons.lang3.concurrent;
 18  
 
 19  
 import java.util.Collections;
 20  
 import java.util.HashMap;
 21  
 import java.util.Map;
 22  
 import java.util.NoSuchElementException;
 23  
 import java.util.Set;
 24  
 import java.util.concurrent.ExecutorService;
 25  
 
 26  
 /**
 27  
  * <p>
 28  
  * A specialized {@link BackgroundInitializer} implementation that can deal with
 29  
  * multiple background initialization tasks.
 30  
  * </p>
 31  
  * <p>
 32  
  * This class has a similar purpose as {@link BackgroundInitializer}. However,
 33  
  * it is not limited to a single background initialization task. Rather it
 34  
  * manages an arbitrary number of {@code BackgroundInitializer} objects,
 35  
  * executes them, and waits until they are completely initialized. This is
 36  
  * useful for applications that have to perform multiple initialization tasks
 37  
  * that can run in parallel (i.e. that do not depend on each other). This class
 38  
  * takes care about the management of an {@code ExecutorService} and shares it
 39  
  * with the {@code BackgroundInitializer} objects it is responsible for; so the
 40  
  * using application need not bother with these details.
 41  
  * </p>
 42  
  * <p>
 43  
  * The typical usage scenario for {@code MultiBackgroundInitializer} is as
 44  
  * follows:
 45  
  * </p>
 46  
  * <ul>
 47  
  * <li>Create a new instance of the class. Optionally pass in a pre-configured
 48  
  * {@code ExecutorService}. Alternatively {@code MultiBackgroundInitializer} can
 49  
  * create a temporary {@code ExecutorService} and delete it after initialization
 50  
  * is complete.</li>
 51  
  * <li>Create specialized {@link BackgroundInitializer} objects for the
 52  
  * initialization tasks to be performed and add them to the {@code
 53  
  * MultiBackgroundInitializer} using the
 54  
  * {@link #addInitializer(String, BackgroundInitializer)} method.</li>
 55  
  * <li>After all initializers have been added, call the {@link #start()} method.
 56  
  * </li>
 57  
  * <li>When access to the result objects produced by the {@code
 58  
  * BackgroundInitializer} objects is needed call the {@link #get()} method. The
 59  
  * object returned here provides access to all result objects created during
 60  
  * initialization. It also stores information about exceptions that have
 61  
  * occurred.</li>
 62  
  * </ul>
 63  
  * <p>
 64  
  * {@code MultiBackgroundInitializer} starts a special controller task that
 65  
  * starts all {@code BackgroundInitializer} objects added to the instance.
 66  
  * Before the an initializer is started it is checked whether this initializer
 67  
  * already has an {@code ExecutorService} set. If this is the case, this {@code
 68  
  * ExecutorService} is used for running the background task. Otherwise the
 69  
  * current {@code ExecutorService} of this {@code MultiBackgroundInitializer} is
 70  
  * shared with the initializer.
 71  
  * </p>
 72  
  * <p>
 73  
  * The easiest way of using this class is to let it deal with the management of
 74  
  * an {@code ExecutorService} itself: If no external {@code ExecutorService} is
 75  
  * provided, the class creates a temporary {@code ExecutorService} (that is
 76  
  * capable of executing all background tasks in parallel) and destroys it at the
 77  
  * end of background processing.
 78  
  * </p>
 79  
  * <p>
 80  
  * Alternatively an external {@code ExecutorService} can be provided - either at
 81  
  * construction time or later by calling the
 82  
  * {@link #setExternalExecutor(ExecutorService)} method. In this case all
 83  
  * background tasks are scheduled at this external {@code ExecutorService}.
 84  
  * <strong>Important note:</strong> When using an external {@code
 85  
  * ExecutorService} be sure that the number of threads managed by the service is
 86  
  * large enough. Otherwise a deadlock can happen! This is the case in the
 87  
  * following scenario: {@code MultiBackgroundInitializer} starts a task that
 88  
  * starts all registered {@code BackgroundInitializer} objects and waits for
 89  
  * their completion. If for instance a single threaded {@code ExecutorService}
 90  
  * is used, none of the background tasks can be executed, and the task created
 91  
  * by {@code MultiBackgroundInitializer} waits forever.
 92  
  * </p>
 93  
  *
 94  
  * @since 3.0
 95  
  */
 96  16
 public class MultiBackgroundInitializer
 97  
         extends
 98  
         BackgroundInitializer<MultiBackgroundInitializer.MultiBackgroundInitializerResults> {
 99  
     /** A map with the child initializers. */
 100  19
     private final Map<String, BackgroundInitializer<?>> childInitializers =
 101  
         new HashMap<String, BackgroundInitializer<?>>();
 102  
 
 103  
     /**
 104  
      * Creates a new instance of {@code MultiBackgroundInitializer}.
 105  
      */
 106  
     public MultiBackgroundInitializer() {
 107  18
         super();
 108  18
     }
 109  
 
 110  
     /**
 111  
      * Creates a new instance of {@code MultiBackgroundInitializer} and
 112  
      * initializes it with the given external {@code ExecutorService}.
 113  
      *
 114  
      * @param exec the {@code ExecutorService} for executing the background
 115  
      * tasks
 116  
      */
 117  
     public MultiBackgroundInitializer(final ExecutorService exec) {
 118  1
         super(exec);
 119  1
     }
 120  
 
 121  
     /**
 122  
      * Adds a new {@code BackgroundInitializer} to this object. When this
 123  
      * {@code MultiBackgroundInitializer} is started, the given initializer will
 124  
      * be processed. This method must not be called after {@link #start()} has
 125  
      * been invoked.
 126  
      *
 127  
      * @param name the name of the initializer (must not be <b>null</b>)
 128  
      * @param init the {@code BackgroundInitializer} to add (must not be
 129  
      * <b>null</b>)
 130  
      * @throws IllegalArgumentException if a required parameter is missing
 131  
      * @throws IllegalStateException if {@code start()} has already been called
 132  
      */
 133  
     public void addInitializer(final String name, final BackgroundInitializer<?> init) {
 134  49
         if (name == null) {
 135  1
             throw new IllegalArgumentException(
 136  
                     "Name of child initializer must not be null!");
 137  
         }
 138  48
         if (init == null) {
 139  1
             throw new IllegalArgumentException(
 140  
                     "Child initializer must not be null!");
 141  
         }
 142  
 
 143  47
         synchronized (this) {
 144  47
             if (isStarted()) {
 145  1
                 throw new IllegalStateException(
 146  
                         "addInitializer() must not be called after start()!");
 147  
             }
 148  46
             childInitializers.put(name, init);
 149  46
         }
 150  46
     }
 151  
 
 152  
     /**
 153  
      * Returns the number of tasks needed for executing all child {@code
 154  
      * BackgroundInitializer} objects in parallel. This implementation sums up
 155  
      * the required tasks for all child initializers (which is necessary if one
 156  
      * of the child initializers is itself a {@code MultiBackgroundInitializer}
 157  
      * ). Then it adds 1 for the control task that waits for the completion of
 158  
      * the children.
 159  
      *
 160  
      * @return the number of tasks required for background processing
 161  
      */
 162  
     @Override
 163  
     protected int getTaskCount() {
 164  15
         int result = 1;
 165  
 
 166  15
         for (final BackgroundInitializer<?> bi : childInitializers.values()) {
 167  41
             result += bi.getTaskCount();
 168  41
         }
 169  
 
 170  15
         return result;
 171  
     }
 172  
 
 173  
     /**
 174  
      * Creates the results object. This implementation starts all child {@code
 175  
      * BackgroundInitializer} objects. Then it collects their results and
 176  
      * creates a {@code MultiBackgroundInitializerResults} object with this
 177  
      * data. If a child initializer throws a checked exceptions, it is added to
 178  
      * the results object. Unchecked exceptions are propagated.
 179  
      *
 180  
      * @return the results object
 181  
      * @throws Exception if an error occurs
 182  
      */
 183  
     @Override
 184  
     protected MultiBackgroundInitializerResults initialize() throws Exception {
 185  
         Map<String, BackgroundInitializer<?>> inits;
 186  16
         synchronized (this) {
 187  
             // create a snapshot to operate on
 188  16
             inits = new HashMap<String, BackgroundInitializer<?>>(
 189  
                     childInitializers);
 190  16
         }
 191  
 
 192  
         // start the child initializers
 193  16
         final ExecutorService exec = getActiveExecutor();
 194  16
         for (final BackgroundInitializer<?> bi : inits.values()) {
 195  46
             if (bi.getExternalExecutor() == null) {
 196  
                 // share the executor service if necessary
 197  45
                 bi.setExternalExecutor(exec);
 198  
             }
 199  46
             bi.start();
 200  46
         }
 201  
 
 202  
         // collect the results
 203  16
         final Map<String, Object> results = new HashMap<String, Object>();
 204  16
         final Map<String, ConcurrentException> excepts = new HashMap<String, ConcurrentException>();
 205  16
         for (final Map.Entry<String, BackgroundInitializer<?>> e : inits.entrySet()) {
 206  
             try {
 207  46
                 results.put(e.getKey(), e.getValue().get());
 208  2
             } catch (final ConcurrentException cex) {
 209  2
                 excepts.put(e.getKey(), cex);
 210  43
             }
 211  45
         }
 212  
 
 213  15
         return new MultiBackgroundInitializerResults(inits, results, excepts);
 214  
     }
 215  
 
 216  
     /**
 217  
      * A data class for storing the results of the background initialization
 218  
      * performed by {@code MultiBackgroundInitializer}. Objects of this inner
 219  
      * class are returned by {@link MultiBackgroundInitializer#initialize()}.
 220  
      * They allow access to all result objects produced by the
 221  
      * {@link BackgroundInitializer} objects managed by the owning instance. It
 222  
      * is also possible to retrieve status information about single
 223  
      * {@link BackgroundInitializer}s, i.e. whether they completed normally or
 224  
      * caused an exception.
 225  
      */
 226  15
     public static class MultiBackgroundInitializerResults {
 227  
         /** A map with the child initializers. */
 228  
         private final Map<String, BackgroundInitializer<?>> initializers;
 229  
 
 230  
         /** A map with the result objects. */
 231  
         private final Map<String, Object> resultObjects;
 232  
 
 233  
         /** A map with the exceptions. */
 234  
         private final Map<String, ConcurrentException> exceptions;
 235  
 
 236  
         /**
 237  
          * Creates a new instance of {@code MultiBackgroundInitializerResults}
 238  
          * and initializes it with maps for the {@code BackgroundInitializer}
 239  
          * objects, their result objects and the exceptions thrown by them.
 240  
          *
 241  
          * @param inits the {@code BackgroundInitializer} objects
 242  
          * @param results the result objects
 243  
          * @param excepts the exceptions
 244  
          */
 245  
         private MultiBackgroundInitializerResults(
 246  
                 final Map<String, BackgroundInitializer<?>> inits,
 247  
                 final Map<String, Object> results,
 248  15
                 final Map<String, ConcurrentException> excepts) {
 249  15
             initializers = inits;
 250  15
             resultObjects = results;
 251  15
             exceptions = excepts;
 252  15
         }
 253  
 
 254  
         /**
 255  
          * Returns the {@code BackgroundInitializer} with the given name. If the
 256  
          * name cannot be resolved, an exception is thrown.
 257  
          *
 258  
          * @param name the name of the {@code BackgroundInitializer}
 259  
          * @return the {@code BackgroundInitializer} with this name
 260  
          * @throws NoSuchElementException if the name cannot be resolved
 261  
          */
 262  
         public BackgroundInitializer<?> getInitializer(final String name) {
 263  40
             return checkName(name);
 264  
         }
 265  
 
 266  
         /**
 267  
          * Returns the result object produced by the {@code
 268  
          * BackgroundInitializer} with the given name. This is the object
 269  
          * returned by the initializer's {@code initialize()} method. If this
 270  
          * {@code BackgroundInitializer} caused an exception, <b>null</b> is
 271  
          * returned. If the name cannot be resolved, an exception is thrown.
 272  
          *
 273  
          * @param name the name of the {@code BackgroundInitializer}
 274  
          * @return the result object produced by this {@code
 275  
          * BackgroundInitializer}
 276  
          * @throws NoSuchElementException if the name cannot be resolved
 277  
          */
 278  
         public Object getResultObject(final String name) {
 279  38
             checkName(name);
 280  37
             return resultObjects.get(name);
 281  
         }
 282  
 
 283  
         /**
 284  
          * Returns a flag whether the {@code BackgroundInitializer} with the
 285  
          * given name caused an exception.
 286  
          *
 287  
          * @param name the name of the {@code BackgroundInitializer}
 288  
          * @return a flag whether this initializer caused an exception
 289  
          * @throws NoSuchElementException if the name cannot be resolved
 290  
          */
 291  
         public boolean isException(final String name) {
 292  37
             checkName(name);
 293  36
             return exceptions.containsKey(name);
 294  
         }
 295  
 
 296  
         /**
 297  
          * Returns the {@code ConcurrentException} object that was thrown by the
 298  
          * {@code BackgroundInitializer} with the given name. If this
 299  
          * initializer did not throw an exception, the return value is
 300  
          * <b>null</b>. If the name cannot be resolved, an exception is thrown.
 301  
          *
 302  
          * @param name the name of the {@code BackgroundInitializer}
 303  
          * @return the exception thrown by this initializer
 304  
          * @throws NoSuchElementException if the name cannot be resolved
 305  
          */
 306  
         public ConcurrentException getException(final String name) {
 307  37
             checkName(name);
 308  36
             return exceptions.get(name);
 309  
         }
 310  
 
 311  
         /**
 312  
          * Returns a set with the names of all {@code BackgroundInitializer}
 313  
          * objects managed by the {@code MultiBackgroundInitializer}.
 314  
          *
 315  
          * @return an (unmodifiable) set with the names of the managed {@code
 316  
          * BackgroundInitializer} objects
 317  
          */
 318  
         public Set<String> initializerNames() {
 319  45
             return Collections.unmodifiableSet(initializers.keySet());
 320  
         }
 321  
 
 322  
         /**
 323  
          * Returns a flag whether the whole initialization was successful. This
 324  
          * is the case if no child initializer has thrown an exception.
 325  
          *
 326  
          * @return a flag whether the initialization was successful
 327  
          */
 328  
         public boolean isSuccessful() {
 329  2
             return exceptions.isEmpty();
 330  
         }
 331  
 
 332  
         /**
 333  
          * Checks whether an initializer with the given name exists. If not,
 334  
          * throws an exception. If it exists, the associated child initializer
 335  
          * is returned.
 336  
          *
 337  
          * @param name the name to check
 338  
          * @return the initializer with this name
 339  
          * @throws NoSuchElementException if the name is unknown
 340  
          */
 341  
         private BackgroundInitializer<?> checkName(final String name) {
 342  152
             final BackgroundInitializer<?> init = initializers.get(name);
 343  152
             if (init == null) {
 344  4
                 throw new NoSuchElementException(
 345  
                         "No child initializer with name " + name);
 346  
             }
 347  
 
 348  148
             return init;
 349  
         }
 350  
     }
 351  
 }