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.Collections; 020import java.util.HashMap; 021import java.util.Map; 022import java.util.NoSuchElementException; 023import java.util.Set; 024import java.util.concurrent.ExecutorService; 025 026/** 027 * <p> 028 * A specialized {@link BackgroundInitializer} implementation that can deal with 029 * multiple background initialization tasks. 030 * </p> 031 * <p> 032 * This class has a similar purpose as {@link BackgroundInitializer}. However, 033 * it is not limited to a single background initialization task. Rather it 034 * manages an arbitrary number of {@code BackgroundInitializer} objects, 035 * executes them, and waits until they are completely initialized. This is 036 * useful for applications that have to perform multiple initialization tasks 037 * that can run in parallel (i.e. that do not depend on each other). This class 038 * takes care about the management of an {@code ExecutorService} and shares it 039 * with the {@code BackgroundInitializer} objects it is responsible for; so the 040 * using application need not bother with these details. 041 * </p> 042 * <p> 043 * The typical usage scenario for {@code MultiBackgroundInitializer} is as 044 * follows: 045 * </p> 046 * <ul> 047 * <li>Create a new instance of the class. Optionally pass in a pre-configured 048 * {@code ExecutorService}. Alternatively {@code MultiBackgroundInitializer} can 049 * create a temporary {@code ExecutorService} and delete it after initialization 050 * is complete.</li> 051 * <li>Create specialized {@link BackgroundInitializer} objects for the 052 * initialization tasks to be performed and add them to the {@code 053 * MultiBackgroundInitializer} using the 054 * {@link #addInitializer(String, BackgroundInitializer)} method.</li> 055 * <li>After all initializers have been added, call the {@link #start()} method. 056 * </li> 057 * <li>When access to the result objects produced by the {@code 058 * BackgroundInitializer} objects is needed call the {@link #get()} method. The 059 * object returned here provides access to all result objects created during 060 * initialization. It also stores information about exceptions that have 061 * occurred.</li> 062 * </ul> 063 * <p> 064 * {@code MultiBackgroundInitializer} starts a special controller task that 065 * starts all {@code BackgroundInitializer} objects added to the instance. 066 * Before the an initializer is started it is checked whether this initializer 067 * already has an {@code ExecutorService} set. If this is the case, this {@code 068 * ExecutorService} is used for running the background task. Otherwise the 069 * current {@code ExecutorService} of this {@code MultiBackgroundInitializer} is 070 * shared with the initializer. 071 * </p> 072 * <p> 073 * The easiest way of using this class is to let it deal with the management of 074 * an {@code ExecutorService} itself: If no external {@code ExecutorService} is 075 * provided, the class creates a temporary {@code ExecutorService} (that is 076 * capable of executing all background tasks in parallel) and destroys it at the 077 * end of background processing. 078 * </p> 079 * <p> 080 * Alternatively an external {@code ExecutorService} can be provided - either at 081 * construction time or later by calling the 082 * {@link #setExternalExecutor(ExecutorService)} method. In this case all 083 * background tasks are scheduled at this external {@code ExecutorService}. 084 * <strong>Important note:</strong> When using an external {@code 085 * ExecutorService} be sure that the number of threads managed by the service is 086 * large enough. Otherwise a deadlock can happen! This is the case in the 087 * following scenario: {@code MultiBackgroundInitializer} starts a task that 088 * starts all registered {@code BackgroundInitializer} objects and waits for 089 * their completion. If for instance a single threaded {@code ExecutorService} 090 * is used, none of the background tasks can be executed, and the task created 091 * by {@code MultiBackgroundInitializer} waits forever. 092 * </p> 093 * 094 * @since 3.0 095 * @version $Id: MultiBackgroundInitializer.java 1583482 2014-03-31 22:54:57Z niallp $ 096 */ 097public class MultiBackgroundInitializer 098 extends 099 BackgroundInitializer<MultiBackgroundInitializer.MultiBackgroundInitializerResults> { 100 /** A map with the child initializers. */ 101 private final Map<String, BackgroundInitializer<?>> childInitializers = 102 new HashMap<String, BackgroundInitializer<?>>(); 103 104 /** 105 * Creates a new instance of {@code MultiBackgroundInitializer}. 106 */ 107 public MultiBackgroundInitializer() { 108 super(); 109 } 110 111 /** 112 * Creates a new instance of {@code MultiBackgroundInitializer} and 113 * initializes it with the given external {@code ExecutorService}. 114 * 115 * @param exec the {@code ExecutorService} for executing the background 116 * tasks 117 */ 118 public MultiBackgroundInitializer(final ExecutorService exec) { 119 super(exec); 120 } 121 122 /** 123 * Adds a new {@code BackgroundInitializer} to this object. When this 124 * {@code MultiBackgroundInitializer} is started, the given initializer will 125 * be processed. This method must not be called after {@link #start()} has 126 * been invoked. 127 * 128 * @param name the name of the initializer (must not be <b>null</b>) 129 * @param init the {@code BackgroundInitializer} to add (must not be 130 * <b>null</b>) 131 * @throws IllegalArgumentException if a required parameter is missing 132 * @throws IllegalStateException if {@code start()} has already been called 133 */ 134 public void addInitializer(final String name, final BackgroundInitializer<?> init) { 135 if (name == null) { 136 throw new IllegalArgumentException( 137 "Name of child initializer must not be null!"); 138 } 139 if (init == null) { 140 throw new IllegalArgumentException( 141 "Child initializer must not be null!"); 142 } 143 144 synchronized (this) { 145 if (isStarted()) { 146 throw new IllegalStateException( 147 "addInitializer() must not be called after start()!"); 148 } 149 childInitializers.put(name, init); 150 } 151 } 152 153 /** 154 * Returns the number of tasks needed for executing all child {@code 155 * BackgroundInitializer} objects in parallel. This implementation sums up 156 * the required tasks for all child initializers (which is necessary if one 157 * of the child initializers is itself a {@code MultiBackgroundInitializer} 158 * ). Then it adds 1 for the control task that waits for the completion of 159 * the children. 160 * 161 * @return the number of tasks required for background processing 162 */ 163 @Override 164 protected int getTaskCount() { 165 int result = 1; 166 167 for (final BackgroundInitializer<?> bi : childInitializers.values()) { 168 result += bi.getTaskCount(); 169 } 170 171 return result; 172 } 173 174 /** 175 * Creates the results object. This implementation starts all child {@code 176 * BackgroundInitializer} objects. Then it collects their results and 177 * creates a {@code MultiBackgroundInitializerResults} object with this 178 * data. If a child initializer throws a checked exceptions, it is added to 179 * the results object. Unchecked exceptions are propagated. 180 * 181 * @return the results object 182 * @throws Exception if an error occurs 183 */ 184 @Override 185 protected MultiBackgroundInitializerResults initialize() throws Exception { 186 Map<String, BackgroundInitializer<?>> inits; 187 synchronized (this) { 188 // create a snapshot to operate on 189 inits = new HashMap<String, BackgroundInitializer<?>>( 190 childInitializers); 191 } 192 193 // start the child initializers 194 final ExecutorService exec = getActiveExecutor(); 195 for (final BackgroundInitializer<?> bi : inits.values()) { 196 if (bi.getExternalExecutor() == null) { 197 // share the executor service if necessary 198 bi.setExternalExecutor(exec); 199 } 200 bi.start(); 201 } 202 203 // collect the results 204 final Map<String, Object> results = new HashMap<String, Object>(); 205 final Map<String, ConcurrentException> excepts = new HashMap<String, ConcurrentException>(); 206 for (final Map.Entry<String, BackgroundInitializer<?>> e : inits.entrySet()) { 207 try { 208 results.put(e.getKey(), e.getValue().get()); 209 } catch (final ConcurrentException cex) { 210 excepts.put(e.getKey(), cex); 211 } 212 } 213 214 return new MultiBackgroundInitializerResults(inits, results, excepts); 215 } 216 217 /** 218 * A data class for storing the results of the background initialization 219 * performed by {@code MultiBackgroundInitializer}. Objects of this inner 220 * class are returned by {@link MultiBackgroundInitializer#initialize()}. 221 * They allow access to all result objects produced by the 222 * {@link BackgroundInitializer} objects managed by the owning instance. It 223 * is also possible to retrieve status information about single 224 * {@link BackgroundInitializer}s, i.e. whether they completed normally or 225 * caused an exception. 226 */ 227 public static class MultiBackgroundInitializerResults { 228 /** A map with the child initializers. */ 229 private final Map<String, BackgroundInitializer<?>> initializers; 230 231 /** A map with the result objects. */ 232 private final Map<String, Object> resultObjects; 233 234 /** A map with the exceptions. */ 235 private final Map<String, ConcurrentException> exceptions; 236 237 /** 238 * Creates a new instance of {@code MultiBackgroundInitializerResults} 239 * and initializes it with maps for the {@code BackgroundInitializer} 240 * objects, their result objects and the exceptions thrown by them. 241 * 242 * @param inits the {@code BackgroundInitializer} objects 243 * @param results the result objects 244 * @param excepts the exceptions 245 */ 246 private MultiBackgroundInitializerResults( 247 final Map<String, BackgroundInitializer<?>> inits, 248 final Map<String, Object> results, 249 final Map<String, ConcurrentException> excepts) { 250 initializers = inits; 251 resultObjects = results; 252 exceptions = excepts; 253 } 254 255 /** 256 * Returns the {@code BackgroundInitializer} with the given name. If the 257 * name cannot be resolved, an exception is thrown. 258 * 259 * @param name the name of the {@code BackgroundInitializer} 260 * @return the {@code BackgroundInitializer} with this name 261 * @throws NoSuchElementException if the name cannot be resolved 262 */ 263 public BackgroundInitializer<?> getInitializer(final String name) { 264 return checkName(name); 265 } 266 267 /** 268 * Returns the result object produced by the {@code 269 * BackgroundInitializer} with the given name. This is the object 270 * returned by the initializer's {@code initialize()} method. If this 271 * {@code BackgroundInitializer} caused an exception, <b>null</b> is 272 * returned. If the name cannot be resolved, an exception is thrown. 273 * 274 * @param name the name of the {@code BackgroundInitializer} 275 * @return the result object produced by this {@code 276 * BackgroundInitializer} 277 * @throws NoSuchElementException if the name cannot be resolved 278 */ 279 public Object getResultObject(final String name) { 280 checkName(name); 281 return resultObjects.get(name); 282 } 283 284 /** 285 * Returns a flag whether the {@code BackgroundInitializer} with the 286 * given name caused an exception. 287 * 288 * @param name the name of the {@code BackgroundInitializer} 289 * @return a flag whether this initializer caused an exception 290 * @throws NoSuchElementException if the name cannot be resolved 291 */ 292 public boolean isException(final String name) { 293 checkName(name); 294 return exceptions.containsKey(name); 295 } 296 297 /** 298 * Returns the {@code ConcurrentException} object that was thrown by the 299 * {@code BackgroundInitializer} with the given name. If this 300 * initializer did not throw an exception, the return value is 301 * <b>null</b>. If the name cannot be resolved, an exception is thrown. 302 * 303 * @param name the name of the {@code BackgroundInitializer} 304 * @return the exception thrown by this initializer 305 * @throws NoSuchElementException if the name cannot be resolved 306 */ 307 public ConcurrentException getException(final String name) { 308 checkName(name); 309 return exceptions.get(name); 310 } 311 312 /** 313 * Returns a set with the names of all {@code BackgroundInitializer} 314 * objects managed by the {@code MultiBackgroundInitializer}. 315 * 316 * @return an (unmodifiable) set with the names of the managed {@code 317 * BackgroundInitializer} objects 318 */ 319 public Set<String> initializerNames() { 320 return Collections.unmodifiableSet(initializers.keySet()); 321 } 322 323 /** 324 * Returns a flag whether the whole initialization was successful. This 325 * is the case if no child initializer has thrown an exception. 326 * 327 * @return a flag whether the initialization was successful 328 */ 329 public boolean isSuccessful() { 330 return exceptions.isEmpty(); 331 } 332 333 /** 334 * Checks whether an initializer with the given name exists. If not, 335 * throws an exception. If it exists, the associated child initializer 336 * is returned. 337 * 338 * @param name the name to check 339 * @return the initializer with this name 340 * @throws NoSuchElementException if the name is unknown 341 */ 342 private BackgroundInitializer<?> checkName(final String name) { 343 final BackgroundInitializer<?> init = initializers.get(name); 344 if (init == null) { 345 throw new NoSuchElementException( 346 "No child initializer with name " + name); 347 } 348 349 return init; 350 } 351 } 352}