J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 3 | * |
| 4 | * This code is free software; you can redistribute it and/or modify it |
| 5 | * under the terms of the GNU General Public License version 2 only, as |
| 6 | * published by the Free Software Foundation. Sun designates this |
| 7 | * particular file as subject to the "Classpath" exception as provided |
| 8 | * by Sun in the LICENSE file that accompanied this code. |
| 9 | * |
| 10 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 13 | * version 2 for more details (a copy is included in the LICENSE file that |
| 14 | * accompanied this code). |
| 15 | * |
| 16 | * You should have received a copy of the GNU General Public License version |
| 17 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 19 | * |
| 20 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 21 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 22 | * have any questions. |
| 23 | */ |
| 24 | |
| 25 | /* |
| 26 | * This file is available under and governed by the GNU General Public |
| 27 | * License version 2 only, as published by the Free Software Foundation. |
| 28 | * However, the following notice accompanied the original version of this |
| 29 | * file: |
| 30 | * |
| 31 | * Written by Doug Lea with assistance from members of JCP JSR-166 |
| 32 | * Expert Group and released to the public domain, as explained at |
| 33 | * http://creativecommons.org/licenses/publicdomain |
| 34 | */ |
| 35 | |
| 36 | package java.util.concurrent; |
| 37 | import java.util.List; |
| 38 | import java.util.Collection; |
| 39 | import java.security.PrivilegedAction; |
| 40 | import java.security.PrivilegedExceptionAction; |
| 41 | |
| 42 | /** |
| 43 | * An {@link Executor} that provides methods to manage termination and |
| 44 | * methods that can produce a {@link Future} for tracking progress of |
| 45 | * one or more asynchronous tasks. |
| 46 | * |
| 47 | * <p> An <tt>ExecutorService</tt> can be shut down, which will cause |
| 48 | * it to reject new tasks. Two different methods are provided for |
| 49 | * shutting down an <tt>ExecutorService</tt>. The {@link #shutdown} |
| 50 | * method will allow previously submitted tasks to execute before |
| 51 | * terminating, while the {@link #shutdownNow} method prevents waiting |
| 52 | * tasks from starting and attempts to stop currently executing tasks. |
| 53 | * Upon termination, an executor has no tasks actively executing, no |
| 54 | * tasks awaiting execution, and no new tasks can be submitted. An |
| 55 | * unused <tt>ExecutorService</tt> should be shut down to allow |
| 56 | * reclamation of its resources. |
| 57 | * |
| 58 | * <p> Method <tt>submit</tt> extends base method {@link |
| 59 | * Executor#execute} by creating and returning a {@link Future} that |
| 60 | * can be used to cancel execution and/or wait for completion. |
| 61 | * Methods <tt>invokeAny</tt> and <tt>invokeAll</tt> perform the most |
| 62 | * commonly useful forms of bulk execution, executing a collection of |
| 63 | * tasks and then waiting for at least one, or all, to |
| 64 | * complete. (Class {@link ExecutorCompletionService} can be used to |
| 65 | * write customized variants of these methods.) |
| 66 | * |
| 67 | * <p>The {@link Executors} class provides factory methods for the |
| 68 | * executor services provided in this package. |
| 69 | * |
| 70 | * <h3>Usage Examples</h3> |
| 71 | * |
| 72 | * Here is a sketch of a network service in which threads in a thread |
| 73 | * pool service incoming requests. It uses the preconfigured {@link |
| 74 | * Executors#newFixedThreadPool} factory method: |
| 75 | * |
| 76 | * <pre> |
| 77 | * class NetworkService implements Runnable { |
| 78 | * private final ServerSocket serverSocket; |
| 79 | * private final ExecutorService pool; |
| 80 | * |
| 81 | * public NetworkService(int port, int poolSize) |
| 82 | * throws IOException { |
| 83 | * serverSocket = new ServerSocket(port); |
| 84 | * pool = Executors.newFixedThreadPool(poolSize); |
| 85 | * } |
| 86 | * |
| 87 | * public void run() { // run the service |
| 88 | * try { |
| 89 | * for (;;) { |
| 90 | * pool.execute(new Handler(serverSocket.accept())); |
| 91 | * } |
| 92 | * } catch (IOException ex) { |
| 93 | * pool.shutdown(); |
| 94 | * } |
| 95 | * } |
| 96 | * } |
| 97 | * |
| 98 | * class Handler implements Runnable { |
| 99 | * private final Socket socket; |
| 100 | * Handler(Socket socket) { this.socket = socket; } |
| 101 | * public void run() { |
| 102 | * // read and service request on socket |
| 103 | * } |
| 104 | * } |
| 105 | * </pre> |
| 106 | * |
| 107 | * The following method shuts down an <tt>ExecutorService</tt> in two phases, |
| 108 | * first by calling <tt>shutdown</tt> to reject incoming tasks, and then |
| 109 | * calling <tt>shutdownNow</tt>, if necessary, to cancel any lingering tasks: |
| 110 | * |
| 111 | * <pre> |
| 112 | * void shutdownAndAwaitTermination(ExecutorService pool) { |
| 113 | * pool.shutdown(); // Disable new tasks from being submitted |
| 114 | * try { |
| 115 | * // Wait a while for existing tasks to terminate |
| 116 | * if (!pool.awaitTermination(60, TimeUnit.SECONDS)) { |
| 117 | * pool.shutdownNow(); // Cancel currently executing tasks |
| 118 | * // Wait a while for tasks to respond to being cancelled |
| 119 | * if (!pool.awaitTermination(60, TimeUnit.SECONDS)) |
| 120 | * System.err.println("Pool did not terminate"); |
| 121 | * } |
| 122 | * } catch (InterruptedException ie) { |
| 123 | * // (Re-)Cancel if current thread also interrupted |
| 124 | * pool.shutdownNow(); |
| 125 | * // Preserve interrupt status |
| 126 | * Thread.currentThread().interrupt(); |
| 127 | * } |
| 128 | * } |
| 129 | * </pre> |
| 130 | * |
| 131 | * <p>Memory consistency effects: Actions in a thread prior to the |
| 132 | * submission of a {@code Runnable} or {@code Callable} task to an |
| 133 | * {@code ExecutorService} |
| 134 | * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
| 135 | * any actions taken by that task, which in turn <i>happen-before</i> the |
| 136 | * result is retrieved via {@code Future.get()}. |
| 137 | * |
| 138 | * @since 1.5 |
| 139 | * @author Doug Lea |
| 140 | */ |
| 141 | public interface ExecutorService extends Executor { |
| 142 | |
| 143 | /** |
| 144 | * Initiates an orderly shutdown in which previously submitted |
| 145 | * tasks are executed, but no new tasks will be accepted. |
| 146 | * Invocation has no additional effect if already shut down. |
| 147 | * |
| 148 | * @throws SecurityException if a security manager exists and |
| 149 | * shutting down this ExecutorService may manipulate |
| 150 | * threads that the caller is not permitted to modify |
| 151 | * because it does not hold {@link |
| 152 | * java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
| 153 | * or the security manager's <tt>checkAccess</tt> method |
| 154 | * denies access. |
| 155 | */ |
| 156 | void shutdown(); |
| 157 | |
| 158 | /** |
| 159 | * Attempts to stop all actively executing tasks, halts the |
| 160 | * processing of waiting tasks, and returns a list of the tasks that were |
| 161 | * awaiting execution. |
| 162 | * |
| 163 | * <p>There are no guarantees beyond best-effort attempts to stop |
| 164 | * processing actively executing tasks. For example, typical |
| 165 | * implementations will cancel via {@link Thread#interrupt}, so any |
| 166 | * task that fails to respond to interrupts may never terminate. |
| 167 | * |
| 168 | * @return list of tasks that never commenced execution |
| 169 | * @throws SecurityException if a security manager exists and |
| 170 | * shutting down this ExecutorService may manipulate |
| 171 | * threads that the caller is not permitted to modify |
| 172 | * because it does not hold {@link |
| 173 | * java.lang.RuntimePermission}<tt>("modifyThread")</tt>, |
| 174 | * or the security manager's <tt>checkAccess</tt> method |
| 175 | * denies access. |
| 176 | */ |
| 177 | List<Runnable> shutdownNow(); |
| 178 | |
| 179 | /** |
| 180 | * Returns <tt>true</tt> if this executor has been shut down. |
| 181 | * |
| 182 | * @return <tt>true</tt> if this executor has been shut down |
| 183 | */ |
| 184 | boolean isShutdown(); |
| 185 | |
| 186 | /** |
| 187 | * Returns <tt>true</tt> if all tasks have completed following shut down. |
| 188 | * Note that <tt>isTerminated</tt> is never <tt>true</tt> unless |
| 189 | * either <tt>shutdown</tt> or <tt>shutdownNow</tt> was called first. |
| 190 | * |
| 191 | * @return <tt>true</tt> if all tasks have completed following shut down |
| 192 | */ |
| 193 | boolean isTerminated(); |
| 194 | |
| 195 | /** |
| 196 | * Blocks until all tasks have completed execution after a shutdown |
| 197 | * request, or the timeout occurs, or the current thread is |
| 198 | * interrupted, whichever happens first. |
| 199 | * |
| 200 | * @param timeout the maximum time to wait |
| 201 | * @param unit the time unit of the timeout argument |
| 202 | * @return <tt>true</tt> if this executor terminated and |
| 203 | * <tt>false</tt> if the timeout elapsed before termination |
| 204 | * @throws InterruptedException if interrupted while waiting |
| 205 | */ |
| 206 | boolean awaitTermination(long timeout, TimeUnit unit) |
| 207 | throws InterruptedException; |
| 208 | |
| 209 | |
| 210 | /** |
| 211 | * Submits a value-returning task for execution and returns a |
| 212 | * Future representing the pending results of the task. The |
| 213 | * Future's <tt>get</tt> method will return the task's result upon |
| 214 | * successful completion. |
| 215 | * |
| 216 | * <p> |
| 217 | * If you would like to immediately block waiting |
| 218 | * for a task, you can use constructions of the form |
| 219 | * <tt>result = exec.submit(aCallable).get();</tt> |
| 220 | * |
| 221 | * <p> Note: The {@link Executors} class includes a set of methods |
| 222 | * that can convert some other common closure-like objects, |
| 223 | * for example, {@link java.security.PrivilegedAction} to |
| 224 | * {@link Callable} form so they can be submitted. |
| 225 | * |
| 226 | * @param task the task to submit |
| 227 | * @return a Future representing pending completion of the task |
| 228 | * @throws RejectedExecutionException if the task cannot be |
| 229 | * scheduled for execution |
| 230 | * @throws NullPointerException if the task is null |
| 231 | */ |
| 232 | <T> Future<T> submit(Callable<T> task); |
| 233 | |
| 234 | /** |
| 235 | * Submits a Runnable task for execution and returns a Future |
| 236 | * representing that task. The Future's <tt>get</tt> method will |
| 237 | * return the given result upon successful completion. |
| 238 | * |
| 239 | * @param task the task to submit |
| 240 | * @param result the result to return |
| 241 | * @return a Future representing pending completion of the task |
| 242 | * @throws RejectedExecutionException if the task cannot be |
| 243 | * scheduled for execution |
| 244 | * @throws NullPointerException if the task is null |
| 245 | */ |
| 246 | <T> Future<T> submit(Runnable task, T result); |
| 247 | |
| 248 | /** |
| 249 | * Submits a Runnable task for execution and returns a Future |
| 250 | * representing that task. The Future's <tt>get</tt> method will |
| 251 | * return <tt>null</tt> upon <em>successful</em> completion. |
| 252 | * |
| 253 | * @param task the task to submit |
| 254 | * @return a Future representing pending completion of the task |
| 255 | * @throws RejectedExecutionException if the task cannot be |
| 256 | * scheduled for execution |
| 257 | * @throws NullPointerException if the task is null |
| 258 | */ |
| 259 | Future<?> submit(Runnable task); |
| 260 | |
| 261 | /** |
| 262 | * Executes the given tasks, returning a list of Futures holding |
| 263 | * their status and results when all complete. |
| 264 | * {@link Future#isDone} is <tt>true</tt> for each |
| 265 | * element of the returned list. |
| 266 | * Note that a <em>completed</em> task could have |
| 267 | * terminated either normally or by throwing an exception. |
| 268 | * The results of this method are undefined if the given |
| 269 | * collection is modified while this operation is in progress. |
| 270 | * |
| 271 | * @param tasks the collection of tasks |
| 272 | * @return A list of Futures representing the tasks, in the same |
| 273 | * sequential order as produced by the iterator for the |
| 274 | * given task list, each of which has completed. |
| 275 | * @throws InterruptedException if interrupted while waiting, in |
| 276 | * which case unfinished tasks are cancelled. |
| 277 | * @throws NullPointerException if tasks or any of its elements are <tt>null</tt> |
| 278 | * @throws RejectedExecutionException if any task cannot be |
| 279 | * scheduled for execution |
| 280 | */ |
| 281 | |
| 282 | <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) |
| 283 | throws InterruptedException; |
| 284 | |
| 285 | /** |
| 286 | * Executes the given tasks, returning a list of Futures holding |
| 287 | * their status and results |
| 288 | * when all complete or the timeout expires, whichever happens first. |
| 289 | * {@link Future#isDone} is <tt>true</tt> for each |
| 290 | * element of the returned list. |
| 291 | * Upon return, tasks that have not completed are cancelled. |
| 292 | * Note that a <em>completed</em> task could have |
| 293 | * terminated either normally or by throwing an exception. |
| 294 | * The results of this method are undefined if the given |
| 295 | * collection is modified while this operation is in progress. |
| 296 | * |
| 297 | * @param tasks the collection of tasks |
| 298 | * @param timeout the maximum time to wait |
| 299 | * @param unit the time unit of the timeout argument |
| 300 | * @return a list of Futures representing the tasks, in the same |
| 301 | * sequential order as produced by the iterator for the |
| 302 | * given task list. If the operation did not time out, |
| 303 | * each task will have completed. If it did time out, some |
| 304 | * of these tasks will not have completed. |
| 305 | * @throws InterruptedException if interrupted while waiting, in |
| 306 | * which case unfinished tasks are cancelled |
| 307 | * @throws NullPointerException if tasks, any of its elements, or |
| 308 | * unit are <tt>null</tt> |
| 309 | * @throws RejectedExecutionException if any task cannot be scheduled |
| 310 | * for execution |
| 311 | */ |
| 312 | <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, |
| 313 | long timeout, TimeUnit unit) |
| 314 | throws InterruptedException; |
| 315 | |
| 316 | /** |
| 317 | * Executes the given tasks, returning the result |
| 318 | * of one that has completed successfully (i.e., without throwing |
| 319 | * an exception), if any do. Upon normal or exceptional return, |
| 320 | * tasks that have not completed are cancelled. |
| 321 | * The results of this method are undefined if the given |
| 322 | * collection is modified while this operation is in progress. |
| 323 | * |
| 324 | * @param tasks the collection of tasks |
| 325 | * @return the result returned by one of the tasks |
| 326 | * @throws InterruptedException if interrupted while waiting |
| 327 | * @throws NullPointerException if tasks or any of its elements |
| 328 | * are <tt>null</tt> |
| 329 | * @throws IllegalArgumentException if tasks is empty |
| 330 | * @throws ExecutionException if no task successfully completes |
| 331 | * @throws RejectedExecutionException if tasks cannot be scheduled |
| 332 | * for execution |
| 333 | */ |
| 334 | <T> T invokeAny(Collection<? extends Callable<T>> tasks) |
| 335 | throws InterruptedException, ExecutionException; |
| 336 | |
| 337 | /** |
| 338 | * Executes the given tasks, returning the result |
| 339 | * of one that has completed successfully (i.e., without throwing |
| 340 | * an exception), if any do before the given timeout elapses. |
| 341 | * Upon normal or exceptional return, tasks that have not |
| 342 | * completed are cancelled. |
| 343 | * The results of this method are undefined if the given |
| 344 | * collection is modified while this operation is in progress. |
| 345 | * |
| 346 | * @param tasks the collection of tasks |
| 347 | * @param timeout the maximum time to wait |
| 348 | * @param unit the time unit of the timeout argument |
| 349 | * @return the result returned by one of the tasks. |
| 350 | * @throws InterruptedException if interrupted while waiting |
| 351 | * @throws NullPointerException if tasks, any of its elements, or |
| 352 | * unit are <tt>null</tt> |
| 353 | * @throws TimeoutException if the given timeout elapses before |
| 354 | * any task successfully completes |
| 355 | * @throws ExecutionException if no task successfully completes |
| 356 | * @throws RejectedExecutionException if tasks cannot be scheduled |
| 357 | * for execution |
| 358 | */ |
| 359 | <T> T invokeAny(Collection<? extends Callable<T>> tasks, |
| 360 | long timeout, TimeUnit unit) |
| 361 | throws InterruptedException, ExecutionException, TimeoutException; |
| 362 | } |