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.Collections; 020 import java.util.HashMap; 021 import java.util.Map; 022 import java.util.NoSuchElementException; 023 import java.util.Set; 024 import 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 * <ul> 046 * <li>Create a new instance of the class. Optionally pass in a pre-configured 047 * {@code ExecutorService}. Alternatively {@code MultiBackgroundInitializer} can 048 * create a temporary {@code ExecutorService} and delete it after initialization 049 * is complete.</li> 050 * <li>Create specialized {@link BackgroundInitializer} objects for the 051 * initialization tasks to be performed and add them to the {@code 052 * MultiBackgroundInitializer} using the 053 * {@link #addInitializer(String, BackgroundInitializer)} method.</li> 054 * <li>After all initializers have been added, call the {@link #start()} method. 055 * </li> 056 * <li>When access to the result objects produced by the {@code 057 * BackgroundInitializer} objects is needed call the {@link #get()} method. The 058 * object returned here provides access to all result objects created during 059 * initialization. It also stores information about exceptions that have 060 * occurred.</li> 061 * </ul> 062 * </p> 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 * @version $Id: MultiBackgroundInitializer.java 889215 2009-12-10 11:56:38Z bayard $ 095 */ 096 public class MultiBackgroundInitializer 097 extends 098 BackgroundInitializer<MultiBackgroundInitializer.MultiBackgroundInitializerResults> { 099 /** A map with the child initializers. */ 100 private final Map<String, BackgroundInitializer<?>> childInitializers = new HashMap<String, BackgroundInitializer<?>>(); 101 102 /** 103 * Creates a new instance of {@code MultiBackgroundInitializer}. 104 */ 105 public MultiBackgroundInitializer() { 106 super(); 107 } 108 109 /** 110 * Creates a new instance of {@code MultiBackgroundInitializer} and 111 * initializes it with the given external {@code ExecutorService}. 112 * 113 * @param exec the {@code ExecutorService} for executing the background 114 * tasks 115 */ 116 public MultiBackgroundInitializer(ExecutorService exec) { 117 super(exec); 118 } 119 120 /** 121 * Adds a new {@code BackgroundInitializer} to this object. When this 122 * {@code MultiBackgroundInitializer} is started, the given initializer will 123 * be processed. This method must not be called after {@link #start()} has 124 * been invoked. 125 * 126 * @param name the name of the initializer (must not be <b>null</b>) 127 * @param init the {@code BackgroundInitializer} to add (must not be 128 * <b>null</b>) 129 * @throws IllegalArgumentException if a required parameter is missing 130 * @throws IllegalStateException if {@code start()} has already been called 131 */ 132 public void addInitializer(String name, BackgroundInitializer<?> init) { 133 if (name == null) { 134 throw new IllegalArgumentException( 135 "Name of child initializer must not be null!"); 136 } 137 if (init == null) { 138 throw new IllegalArgumentException( 139 "Child initializer must not be null!"); 140 } 141 142 synchronized (this) { 143 if (isStarted()) { 144 throw new IllegalStateException( 145 "addInitializer() must not be called after start()!"); 146 } 147 childInitializers.put(name, init); 148 } 149 } 150 151 /** 152 * Returns the number of tasks needed for executing all child {@code 153 * BackgroundInitializer} objects in parallel. This implementation sums up 154 * the required tasks for all child initializers (which is necessary if one 155 * of the child initializers is itself a {@code MultiBackgroundInitializer} 156 * ). Then it adds 1 for the control task that waits for the completion of 157 * the children. 158 * 159 * @return the number of tasks required for background processing 160 */ 161 @Override 162 protected int getTaskCount() { 163 int result = 1; 164 165 for (BackgroundInitializer<?> bi : childInitializers.values()) { 166 result += bi.getTaskCount(); 167 } 168 169 return result; 170 } 171 172 /** 173 * Creates the results object. This implementation starts all child {@code 174 * BackgroundInitializer} objects. Then it collects their results and 175 * creates a {@code MultiBackgroundInitializerResults} object with this 176 * data. If a child initializer throws a checked exceptions, it is added to 177 * the results object. Unchecked exceptions are propagated. 178 * 179 * @return the results object 180 * @throws Exception if an error occurs 181 */ 182 @Override 183 protected MultiBackgroundInitializerResults initialize() throws Exception { 184 Map<String, BackgroundInitializer<?>> inits; 185 synchronized (this) { 186 // create a snapshot to operate on 187 inits = new HashMap<String, BackgroundInitializer<?>>( 188 childInitializers); 189 } 190 191 // start the child initializers 192 ExecutorService exec = getActiveExecutor(); 193 for (BackgroundInitializer<?> bi : inits.values()) { 194 if (bi.getExternalExecutor() == null) { 195 // share the executor service if necessary 196 bi.setExternalExecutor(exec); 197 } 198 bi.start(); 199 } 200 201 // collect the results 202 Map<String, Object> results = new HashMap<String, Object>(); 203 Map<String, ConcurrentException> excepts = new HashMap<String, ConcurrentException>(); 204 for (Map.Entry<String, BackgroundInitializer<?>> e : inits.entrySet()) { 205 try { 206 results.put(e.getKey(), e.getValue().get()); 207 } catch (ConcurrentException cex) { 208 excepts.put(e.getKey(), cex); 209 } 210 } 211 212 return new MultiBackgroundInitializerResults(inits, results, excepts); 213 } 214 215 /** 216 * A data class for storing the results of the background initialization 217 * performed by {@code MultiBackgroundInitializer}. Objects of this inner 218 * class are returned by {@link MultiBackgroundInitializer#initialize()}. 219 * They allow access to all result objects produced by the 220 * {@link BackgroundInitializer} objects managed by the owning instance. It 221 * is also possible to retrieve status information about single 222 * {@link BackgroundInitializer}s, i.e. whether they completed normally or 223 * caused an exception. 224 */ 225 public static class MultiBackgroundInitializerResults { 226 /** A map with the child initializers. */ 227 private final Map<String, BackgroundInitializer<?>> initializers; 228 229 /** A map with the result objects. */ 230 private final Map<String, Object> resultObjects; 231 232 /** A map with the exceptions. */ 233 private final Map<String, ConcurrentException> exceptions; 234 235 /** 236 * Creates a new instance of {@code MultiBackgroundInitializerResults} 237 * and initializes it with maps for the {@code BackgroundInitializer} 238 * objects, their result objects and the exceptions thrown by them. 239 * 240 * @param inits the {@code BackgroundInitializer} objects 241 * @param results the result objects 242 * @param excepts the exceptions 243 */ 244 private MultiBackgroundInitializerResults( 245 Map<String, BackgroundInitializer<?>> inits, 246 Map<String, Object> results, 247 Map<String, ConcurrentException> excepts) { 248 initializers = inits; 249 resultObjects = results; 250 exceptions = excepts; 251 } 252 253 /** 254 * Returns the {@code BackgroundInitializer} with the given name. If the 255 * name cannot be resolved, an exception is thrown. 256 * 257 * @param name the name of the {@code BackgroundInitializer} 258 * @return the {@code BackgroundInitializer} with this name 259 * @throws NoSuchElementException if the name cannot be resolved 260 */ 261 public BackgroundInitializer<?> getInitializer(String name) { 262 return checkName(name); 263 } 264 265 /** 266 * Returns the result object produced by the {@code 267 * BackgroundInitializer} with the given name. This is the object 268 * returned by the initializer's {@code initialize()} method. If this 269 * {@code BackgroundInitializer} caused an exception, <b>null</b> is 270 * returned. If the name cannot be resolved, an exception is thrown. 271 * 272 * @param name the name of the {@code BackgroundInitializer} 273 * @return the result object produced by this {@code 274 * BackgroundInitializer} 275 * @throws NoSuchElementException if the name cannot be resolved 276 */ 277 public Object getResultObject(String name) { 278 checkName(name); 279 return resultObjects.get(name); 280 } 281 282 /** 283 * Returns a flag whether the {@code BackgroundInitializer} with the 284 * given name caused an exception. 285 * 286 * @param name the name of the {@code BackgroundInitializer} 287 * @return a flag whether this initializer caused an exception 288 * @throws NoSuchElementException if the name cannot be resolved 289 */ 290 public boolean isException(String name) { 291 checkName(name); 292 return exceptions.containsKey(name); 293 } 294 295 /** 296 * Returns the {@code ConcurrentException} object that was thrown by the 297 * {@code BackgroundInitializer} with the given name. If this 298 * initializer did not throw an exception, the return value is 299 * <b>null</b>. If the name cannot be resolved, an exception is thrown. 300 * 301 * @param name the name of the {@code BackgroundInitializer} 302 * @return the exception thrown by this initializer 303 * @throws NoSuchElementException if the name cannot be resolved 304 */ 305 public ConcurrentException getException(String name) { 306 checkName(name); 307 return exceptions.get(name); 308 } 309 310 /** 311 * Returns a set with the names of all {@code BackgroundInitializer} 312 * objects managed by the {@code MultiBackgroundInitializer}. 313 * 314 * @return an (unmodifiable) set with the names of the managed {@code 315 * BackgroundInitializer} objects 316 */ 317 public Set<String> initializerNames() { 318 return Collections.unmodifiableSet(initializers.keySet()); 319 } 320 321 /** 322 * Checks whether an initializer with the given name exists. If not, 323 * throws an exception. If it exists, the associated child initializer 324 * is returned. 325 * 326 * @param name the name to check 327 * @return the initializer with this name 328 * @throws NoSuchElementException if the name is unknown 329 */ 330 private BackgroundInitializer<?> checkName(String name) { 331 BackgroundInitializer<?> init = initializers.get(name); 332 if (init == null) { 333 throw new NoSuchElementException( 334 "No child initializer with name " + name); 335 } 336 337 return init; 338 } 339 } 340 }