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.concurrent.locks.*; |
| 38 | import java.util.concurrent.atomic.*; |
| 39 | import java.util.*; |
| 40 | |
| 41 | /** |
| 42 | * An {@link ExecutorService} that executes each submitted task using |
| 43 | * one of possibly several pooled threads, normally configured |
| 44 | * using {@link Executors} factory methods. |
| 45 | * |
| 46 | * <p>Thread pools address two different problems: they usually |
| 47 | * provide improved performance when executing large numbers of |
| 48 | * asynchronous tasks, due to reduced per-task invocation overhead, |
| 49 | * and they provide a means of bounding and managing the resources, |
| 50 | * including threads, consumed when executing a collection of tasks. |
| 51 | * Each {@code ThreadPoolExecutor} also maintains some basic |
| 52 | * statistics, such as the number of completed tasks. |
| 53 | * |
| 54 | * <p>To be useful across a wide range of contexts, this class |
| 55 | * provides many adjustable parameters and extensibility |
| 56 | * hooks. However, programmers are urged to use the more convenient |
| 57 | * {@link Executors} factory methods {@link |
| 58 | * Executors#newCachedThreadPool} (unbounded thread pool, with |
| 59 | * automatic thread reclamation), {@link Executors#newFixedThreadPool} |
| 60 | * (fixed size thread pool) and {@link |
| 61 | * Executors#newSingleThreadExecutor} (single background thread), that |
| 62 | * preconfigure settings for the most common usage |
| 63 | * scenarios. Otherwise, use the following guide when manually |
| 64 | * configuring and tuning this class: |
| 65 | * |
| 66 | * <dl> |
| 67 | * |
| 68 | * <dt>Core and maximum pool sizes</dt> |
| 69 | * |
| 70 | * <dd>A {@code ThreadPoolExecutor} will automatically adjust the |
| 71 | * pool size (see {@link #getPoolSize}) |
| 72 | * according to the bounds set by |
| 73 | * corePoolSize (see {@link #getCorePoolSize}) and |
| 74 | * maximumPoolSize (see {@link #getMaximumPoolSize}). |
| 75 | * |
| 76 | * When a new task is submitted in method {@link #execute}, and fewer |
| 77 | * than corePoolSize threads are running, a new thread is created to |
| 78 | * handle the request, even if other worker threads are idle. If |
| 79 | * there are more than corePoolSize but less than maximumPoolSize |
| 80 | * threads running, a new thread will be created only if the queue is |
| 81 | * full. By setting corePoolSize and maximumPoolSize the same, you |
| 82 | * create a fixed-size thread pool. By setting maximumPoolSize to an |
| 83 | * essentially unbounded value such as {@code Integer.MAX_VALUE}, you |
| 84 | * allow the pool to accommodate an arbitrary number of concurrent |
| 85 | * tasks. Most typically, core and maximum pool sizes are set only |
| 86 | * upon construction, but they may also be changed dynamically using |
| 87 | * {@link #setCorePoolSize} and {@link #setMaximumPoolSize}. </dd> |
| 88 | * |
| 89 | * <dt>On-demand construction</dt> |
| 90 | * |
| 91 | * <dd> By default, even core threads are initially created and |
| 92 | * started only when new tasks arrive, but this can be overridden |
| 93 | * dynamically using method {@link #prestartCoreThread} or {@link |
| 94 | * #prestartAllCoreThreads}. You probably want to prestart threads if |
| 95 | * you construct the pool with a non-empty queue. </dd> |
| 96 | * |
| 97 | * <dt>Creating new threads</dt> |
| 98 | * |
| 99 | * <dd>New threads are created using a {@link ThreadFactory}. If not |
| 100 | * otherwise specified, a {@link Executors#defaultThreadFactory} is |
| 101 | * used, that creates threads to all be in the same {@link |
| 102 | * ThreadGroup} and with the same {@code NORM_PRIORITY} priority and |
| 103 | * non-daemon status. By supplying a different ThreadFactory, you can |
| 104 | * alter the thread's name, thread group, priority, daemon status, |
| 105 | * etc. If a {@code ThreadFactory} fails to create a thread when asked |
| 106 | * by returning null from {@code newThread}, the executor will |
| 107 | * continue, but might not be able to execute any tasks. Threads |
| 108 | * should possess the "modifyThread" {@code RuntimePermission}. If |
| 109 | * worker threads or other threads using the pool do not possess this |
| 110 | * permission, service may be degraded: configuration changes may not |
| 111 | * take effect in a timely manner, and a shutdown pool may remain in a |
| 112 | * state in which termination is possible but not completed.</dd> |
| 113 | * |
| 114 | * <dt>Keep-alive times</dt> |
| 115 | * |
| 116 | * <dd>If the pool currently has more than corePoolSize threads, |
| 117 | * excess threads will be terminated if they have been idle for more |
| 118 | * than the keepAliveTime (see {@link #getKeepAliveTime}). This |
| 119 | * provides a means of reducing resource consumption when the pool is |
| 120 | * not being actively used. If the pool becomes more active later, new |
| 121 | * threads will be constructed. This parameter can also be changed |
| 122 | * dynamically using method {@link #setKeepAliveTime}. Using a value |
| 123 | * of {@code Long.MAX_VALUE} {@link TimeUnit#NANOSECONDS} effectively |
| 124 | * disables idle threads from ever terminating prior to shut down. By |
| 125 | * default, the keep-alive policy applies only when there are more |
| 126 | * than corePoolSizeThreads. But method {@link |
| 127 | * #allowCoreThreadTimeOut(boolean)} can be used to apply this |
| 128 | * time-out policy to core threads as well, so long as the |
| 129 | * keepAliveTime value is non-zero. </dd> |
| 130 | * |
| 131 | * <dt>Queuing</dt> |
| 132 | * |
| 133 | * <dd>Any {@link BlockingQueue} may be used to transfer and hold |
| 134 | * submitted tasks. The use of this queue interacts with pool sizing: |
| 135 | * |
| 136 | * <ul> |
| 137 | * |
| 138 | * <li> If fewer than corePoolSize threads are running, the Executor |
| 139 | * always prefers adding a new thread |
| 140 | * rather than queuing.</li> |
| 141 | * |
| 142 | * <li> If corePoolSize or more threads are running, the Executor |
| 143 | * always prefers queuing a request rather than adding a new |
| 144 | * thread.</li> |
| 145 | * |
| 146 | * <li> If a request cannot be queued, a new thread is created unless |
| 147 | * this would exceed maximumPoolSize, in which case, the task will be |
| 148 | * rejected.</li> |
| 149 | * |
| 150 | * </ul> |
| 151 | * |
| 152 | * There are three general strategies for queuing: |
| 153 | * <ol> |
| 154 | * |
| 155 | * <li> <em> Direct handoffs.</em> A good default choice for a work |
| 156 | * queue is a {@link SynchronousQueue} that hands off tasks to threads |
| 157 | * without otherwise holding them. Here, an attempt to queue a task |
| 158 | * will fail if no threads are immediately available to run it, so a |
| 159 | * new thread will be constructed. This policy avoids lockups when |
| 160 | * handling sets of requests that might have internal dependencies. |
| 161 | * Direct handoffs generally require unbounded maximumPoolSizes to |
| 162 | * avoid rejection of new submitted tasks. This in turn admits the |
| 163 | * possibility of unbounded thread growth when commands continue to |
| 164 | * arrive on average faster than they can be processed. </li> |
| 165 | * |
| 166 | * <li><em> Unbounded queues.</em> Using an unbounded queue (for |
| 167 | * example a {@link LinkedBlockingQueue} without a predefined |
| 168 | * capacity) will cause new tasks to wait in the queue when all |
| 169 | * corePoolSize threads are busy. Thus, no more than corePoolSize |
| 170 | * threads will ever be created. (And the value of the maximumPoolSize |
| 171 | * therefore doesn't have any effect.) This may be appropriate when |
| 172 | * each task is completely independent of others, so tasks cannot |
| 173 | * affect each others execution; for example, in a web page server. |
| 174 | * While this style of queuing can be useful in smoothing out |
| 175 | * transient bursts of requests, it admits the possibility of |
| 176 | * unbounded work queue growth when commands continue to arrive on |
| 177 | * average faster than they can be processed. </li> |
| 178 | * |
| 179 | * <li><em>Bounded queues.</em> A bounded queue (for example, an |
| 180 | * {@link ArrayBlockingQueue}) helps prevent resource exhaustion when |
| 181 | * used with finite maximumPoolSizes, but can be more difficult to |
| 182 | * tune and control. Queue sizes and maximum pool sizes may be traded |
| 183 | * off for each other: Using large queues and small pools minimizes |
| 184 | * CPU usage, OS resources, and context-switching overhead, but can |
| 185 | * lead to artificially low throughput. If tasks frequently block (for |
| 186 | * example if they are I/O bound), a system may be able to schedule |
| 187 | * time for more threads than you otherwise allow. Use of small queues |
| 188 | * generally requires larger pool sizes, which keeps CPUs busier but |
| 189 | * may encounter unacceptable scheduling overhead, which also |
| 190 | * decreases throughput. </li> |
| 191 | * |
| 192 | * </ol> |
| 193 | * |
| 194 | * </dd> |
| 195 | * |
| 196 | * <dt>Rejected tasks</dt> |
| 197 | * |
| 198 | * <dd> New tasks submitted in method {@link #execute} will be |
| 199 | * <em>rejected</em> when the Executor has been shut down, and also |
| 200 | * when the Executor uses finite bounds for both maximum threads and |
| 201 | * work queue capacity, and is saturated. In either case, the {@code |
| 202 | * execute} method invokes the {@link |
| 203 | * RejectedExecutionHandler#rejectedExecution} method of its {@link |
| 204 | * RejectedExecutionHandler}. Four predefined handler policies are |
| 205 | * provided: |
| 206 | * |
| 207 | * <ol> |
| 208 | * |
| 209 | * <li> In the default {@link ThreadPoolExecutor.AbortPolicy}, the |
| 210 | * handler throws a runtime {@link RejectedExecutionException} upon |
| 211 | * rejection. </li> |
| 212 | * |
| 213 | * <li> In {@link ThreadPoolExecutor.CallerRunsPolicy}, the thread |
| 214 | * that invokes {@code execute} itself runs the task. This provides a |
| 215 | * simple feedback control mechanism that will slow down the rate that |
| 216 | * new tasks are submitted. </li> |
| 217 | * |
| 218 | * <li> In {@link ThreadPoolExecutor.DiscardPolicy}, a task that |
| 219 | * cannot be executed is simply dropped. </li> |
| 220 | * |
| 221 | * <li>In {@link ThreadPoolExecutor.DiscardOldestPolicy}, if the |
| 222 | * executor is not shut down, the task at the head of the work queue |
| 223 | * is dropped, and then execution is retried (which can fail again, |
| 224 | * causing this to be repeated.) </li> |
| 225 | * |
| 226 | * </ol> |
| 227 | * |
| 228 | * It is possible to define and use other kinds of {@link |
| 229 | * RejectedExecutionHandler} classes. Doing so requires some care |
| 230 | * especially when policies are designed to work only under particular |
| 231 | * capacity or queuing policies. </dd> |
| 232 | * |
| 233 | * <dt>Hook methods</dt> |
| 234 | * |
| 235 | * <dd>This class provides {@code protected} overridable {@link |
| 236 | * #beforeExecute} and {@link #afterExecute} methods that are called |
| 237 | * before and after execution of each task. These can be used to |
| 238 | * manipulate the execution environment; for example, reinitializing |
| 239 | * ThreadLocals, gathering statistics, or adding log |
| 240 | * entries. Additionally, method {@link #terminated} can be overridden |
| 241 | * to perform any special processing that needs to be done once the |
| 242 | * Executor has fully terminated. |
| 243 | * |
| 244 | * <p>If hook or callback methods throw exceptions, internal worker |
| 245 | * threads may in turn fail and abruptly terminate.</dd> |
| 246 | * |
| 247 | * <dt>Queue maintenance</dt> |
| 248 | * |
| 249 | * <dd> Method {@link #getQueue} allows access to the work queue for |
| 250 | * purposes of monitoring and debugging. Use of this method for any |
| 251 | * other purpose is strongly discouraged. Two supplied methods, |
| 252 | * {@link #remove} and {@link #purge} are available to assist in |
| 253 | * storage reclamation when large numbers of queued tasks become |
| 254 | * cancelled.</dd> |
| 255 | * |
| 256 | * <dt>Finalization</dt> |
| 257 | * |
| 258 | * <dd> A pool that is no longer referenced in a program <em>AND</em> |
| 259 | * has no remaining threads will be {@code shutdown} automatically. If |
| 260 | * you would like to ensure that unreferenced pools are reclaimed even |
| 261 | * if users forget to call {@link #shutdown}, then you must arrange |
| 262 | * that unused threads eventually die, by setting appropriate |
| 263 | * keep-alive times, using a lower bound of zero core threads and/or |
| 264 | * setting {@link #allowCoreThreadTimeOut(boolean)}. </dd> |
| 265 | * |
| 266 | * </dl> |
| 267 | * |
| 268 | * <p> <b>Extension example</b>. Most extensions of this class |
| 269 | * override one or more of the protected hook methods. For example, |
| 270 | * here is a subclass that adds a simple pause/resume feature: |
| 271 | * |
| 272 | * <pre> {@code |
| 273 | * class PausableThreadPoolExecutor extends ThreadPoolExecutor { |
| 274 | * private boolean isPaused; |
| 275 | * private ReentrantLock pauseLock = new ReentrantLock(); |
| 276 | * private Condition unpaused = pauseLock.newCondition(); |
| 277 | * |
| 278 | * public PausableThreadPoolExecutor(...) { super(...); } |
| 279 | * |
| 280 | * protected void beforeExecute(Thread t, Runnable r) { |
| 281 | * super.beforeExecute(t, r); |
| 282 | * pauseLock.lock(); |
| 283 | * try { |
| 284 | * while (isPaused) unpaused.await(); |
| 285 | * } catch (InterruptedException ie) { |
| 286 | * t.interrupt(); |
| 287 | * } finally { |
| 288 | * pauseLock.unlock(); |
| 289 | * } |
| 290 | * } |
| 291 | * |
| 292 | * public void pause() { |
| 293 | * pauseLock.lock(); |
| 294 | * try { |
| 295 | * isPaused = true; |
| 296 | * } finally { |
| 297 | * pauseLock.unlock(); |
| 298 | * } |
| 299 | * } |
| 300 | * |
| 301 | * public void resume() { |
| 302 | * pauseLock.lock(); |
| 303 | * try { |
| 304 | * isPaused = false; |
| 305 | * unpaused.signalAll(); |
| 306 | * } finally { |
| 307 | * pauseLock.unlock(); |
| 308 | * } |
| 309 | * } |
| 310 | * }}</pre> |
| 311 | * |
| 312 | * @since 1.5 |
| 313 | * @author Doug Lea |
| 314 | */ |
| 315 | public class ThreadPoolExecutor extends AbstractExecutorService { |
| 316 | /** |
| 317 | * The main pool control state, ctl, is an atomic integer packing |
| 318 | * two conceptual fields |
| 319 | * workerCount, indicating the effective number of threads |
| 320 | * runState, indicating whether running, shutting down etc |
| 321 | * |
| 322 | * In order to pack them into one int, we limit workerCount to |
| 323 | * (2^29)-1 (about 500 million) threads rather than (2^31)-1 (2 |
| 324 | * billion) otherwise representable. If this is ever an issue in |
| 325 | * the future, the variable can be changed to be an AtomicLong, |
| 326 | * and the shift/mask constants below adjusted. But until the need |
| 327 | * arises, this code is a bit faster and simpler using an int. |
| 328 | * |
| 329 | * The workerCount is the number of workers that have been |
| 330 | * permitted to start and not permitted to stop. The value may be |
| 331 | * transiently different from the actual number of live threads, |
| 332 | * for example when a ThreadFactory fails to create a thread when |
| 333 | * asked, and when exiting threads are still performing |
| 334 | * bookkeeping before terminating. The user-visible pool size is |
| 335 | * reported as the current size of the workers set. |
| 336 | * |
| 337 | * The runState provides the main lifecyle control, taking on values: |
| 338 | * |
| 339 | * RUNNING: Accept new tasks and process queued tasks |
| 340 | * SHUTDOWN: Don't accept new tasks, but process queued tasks |
| 341 | * STOP: Don't accept new tasks, don't process queued tasks, |
| 342 | * and interrupt in-progress tasks |
| 343 | * TIDYING: All tasks have terminated, workerCount is zero, |
| 344 | * the thread transitioning to state TIDYING |
| 345 | * will run the terminated() hook method |
| 346 | * TERMINATED: terminated() has completed |
| 347 | * |
| 348 | * The numerical order among these values matters, to allow |
| 349 | * ordered comparisons. The runState monotonically increases over |
| 350 | * time, but need not hit each state. The transitions are: |
| 351 | * |
| 352 | * RUNNING -> SHUTDOWN |
| 353 | * On invocation of shutdown(), perhaps implicitly in finalize() |
| 354 | * (RUNNING or SHUTDOWN) -> STOP |
| 355 | * On invocation of shutdownNow() |
| 356 | * SHUTDOWN -> TIDYING |
| 357 | * When both queue and pool are empty |
| 358 | * STOP -> TIDYING |
| 359 | * When pool is empty |
| 360 | * TIDYING -> TERMINATED |
| 361 | * When the terminated() hook method has completed |
| 362 | * |
| 363 | * Threads waiting in awaitTermination() will return when the |
| 364 | * state reaches TERMINATED. |
| 365 | * |
| 366 | * Detecting the transition from SHUTDOWN to TIDYING is less |
| 367 | * straightforward than you'd like because the queue may become |
| 368 | * empty after non-empty and vice versa during SHUTDOWN state, but |
| 369 | * we can only terminate if, after seeing that it is empty, we see |
| 370 | * that workerCount is 0 (which sometimes entails a recheck -- see |
| 371 | * below). |
| 372 | */ |
| 373 | private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0)); |
| 374 | private static final int COUNT_BITS = Integer.SIZE - 3; |
| 375 | private static final int CAPACITY = (1 << COUNT_BITS) - 1; |
| 376 | |
| 377 | // runState is stored in the high-order bits |
| 378 | private static final int RUNNING = -1 << COUNT_BITS; |
| 379 | private static final int SHUTDOWN = 0 << COUNT_BITS; |
| 380 | private static final int STOP = 1 << COUNT_BITS; |
| 381 | private static final int TIDYING = 2 << COUNT_BITS; |
| 382 | private static final int TERMINATED = 3 << COUNT_BITS; |
| 383 | |
| 384 | // Packing and unpacking ctl |
| 385 | private static int runStateOf(int c) { return c & ~CAPACITY; } |
| 386 | private static int workerCountOf(int c) { return c & CAPACITY; } |
| 387 | private static int ctlOf(int rs, int wc) { return rs | wc; } |
| 388 | |
| 389 | /* |
| 390 | * Bit field accessors that don't require unpacking ctl. |
| 391 | * These depend on the bit layout and on workerCount being never negative. |
| 392 | */ |
| 393 | |
| 394 | private static boolean runStateLessThan(int c, int s) { |
| 395 | return c < s; |
| 396 | } |
| 397 | |
| 398 | private static boolean runStateAtLeast(int c, int s) { |
| 399 | return c >= s; |
| 400 | } |
| 401 | |
| 402 | private static boolean isRunning(int c) { |
| 403 | return c < SHUTDOWN; |
| 404 | } |
| 405 | |
| 406 | /** |
| 407 | * Attempt to CAS-increment the workerCount field of ctl. |
| 408 | */ |
| 409 | private boolean compareAndIncrementWorkerCount(int expect) { |
| 410 | return ctl.compareAndSet(expect, expect + 1); |
| 411 | } |
| 412 | |
| 413 | /** |
| 414 | * Attempt to CAS-decrement the workerCount field of ctl. |
| 415 | */ |
| 416 | private boolean compareAndDecrementWorkerCount(int expect) { |
| 417 | return ctl.compareAndSet(expect, expect - 1); |
| 418 | } |
| 419 | |
| 420 | /** |
| 421 | * Decrements the workerCount field of ctl. This is called only on |
| 422 | * abrupt termination of a thread (see processWorkerExit). Other |
| 423 | * decrements are performed within getTask. |
| 424 | */ |
| 425 | private void decrementWorkerCount() { |
| 426 | do {} while (! compareAndDecrementWorkerCount(ctl.get())); |
| 427 | } |
| 428 | |
| 429 | /** |
| 430 | * The queue used for holding tasks and handing off to worker |
| 431 | * threads. We do not require that workQueue.poll() returning |
| 432 | * null necessarily means that workQueue.isEmpty(), so rely |
| 433 | * solely on isEmpty to see if the queue is empty (which we must |
| 434 | * do for example when deciding whether to transition from |
| 435 | * SHUTDOWN to TIDYING). This accommodates special-purpose |
| 436 | * queues such as DelayQueues for which poll() is allowed to |
| 437 | * return null even if it may later return non-null when delays |
| 438 | * expire. |
| 439 | */ |
| 440 | private final BlockingQueue<Runnable> workQueue; |
| 441 | |
| 442 | /** |
| 443 | * Lock held on access to workers set and related bookkeeping. |
| 444 | * While we could use a concurrent set of some sort, it turns out |
| 445 | * to be generally preferable to use a lock. Among the reasons is |
| 446 | * that this serializes interruptIdleWorkers, which avoids |
| 447 | * unnecessary interrupt storms, especially during shutdown. |
| 448 | * Otherwise exiting threads would concurrently interrupt those |
| 449 | * that have not yet interrupted. It also simplifies some of the |
| 450 | * associated statistics bookkeeping of largestPoolSize etc. We |
| 451 | * also hold mainLock on shutdown and shutdownNow, for the sake of |
| 452 | * ensuring workers set is stable while separately checking |
| 453 | * permission to interrupt and actually interrupting. |
| 454 | */ |
| 455 | private final ReentrantLock mainLock = new ReentrantLock(); |
| 456 | |
| 457 | /** |
| 458 | * Set containing all worker threads in pool. Accessed only when |
| 459 | * holding mainLock. |
| 460 | */ |
| 461 | private final HashSet<Worker> workers = new HashSet<Worker>(); |
| 462 | |
| 463 | /** |
| 464 | * Wait condition to support awaitTermination |
| 465 | */ |
| 466 | private final Condition termination = mainLock.newCondition(); |
| 467 | |
| 468 | /** |
| 469 | * Tracks largest attained pool size. Accessed only under |
| 470 | * mainLock. |
| 471 | */ |
| 472 | private int largestPoolSize; |
| 473 | |
| 474 | /** |
| 475 | * Counter for completed tasks. Updated only on termination of |
| 476 | * worker threads. Accessed only under mainLock. |
| 477 | */ |
| 478 | private long completedTaskCount; |
| 479 | |
| 480 | /* |
| 481 | * All user control parameters are declared as volatiles so that |
| 482 | * ongoing actions are based on freshest values, but without need |
| 483 | * for locking, since no internal invariants depend on them |
| 484 | * changing synchronously with respect to other actions. |
| 485 | */ |
| 486 | |
| 487 | /** |
| 488 | * Factory for new threads. All threads are created using this |
| 489 | * factory (via method addWorker). All callers must be prepared |
| 490 | * for addWorker to fail, which may reflect a system or user's |
| 491 | * policy limiting the number of threads. Even though it is not |
| 492 | * treated as an error, failure to create threads may result in |
| 493 | * new tasks being rejected or existing ones remaining stuck in |
| 494 | * the queue. On the other hand, no special precautions exist to |
| 495 | * handle OutOfMemoryErrors that might be thrown while trying to |
| 496 | * create threads, since there is generally no recourse from |
| 497 | * within this class. |
| 498 | */ |
| 499 | private volatile ThreadFactory threadFactory; |
| 500 | |
| 501 | /** |
| 502 | * Handler called when saturated or shutdown in execute. |
| 503 | */ |
| 504 | private volatile RejectedExecutionHandler handler; |
| 505 | |
| 506 | /** |
| 507 | * Timeout in nanoseconds for idle threads waiting for work. |
| 508 | * Threads use this timeout when there are more than corePoolSize |
| 509 | * present or if allowCoreThreadTimeOut. Otherwise they wait |
| 510 | * forever for new work. |
| 511 | */ |
| 512 | private volatile long keepAliveTime; |
| 513 | |
| 514 | /** |
| 515 | * If false (default), core threads stay alive even when idle. |
| 516 | * If true, core threads use keepAliveTime to time out waiting |
| 517 | * for work. |
| 518 | */ |
| 519 | private volatile boolean allowCoreThreadTimeOut; |
| 520 | |
| 521 | /** |
| 522 | * Core pool size is the minimum number of workers to keep alive |
| 523 | * (and not allow to time out etc) unless allowCoreThreadTimeOut |
| 524 | * is set, in which case the minimum is zero. |
| 525 | */ |
| 526 | private volatile int corePoolSize; |
| 527 | |
| 528 | /** |
| 529 | * Maximum pool size. Note that the actual maximum is internally |
| 530 | * bounded by CAPACITY. |
| 531 | */ |
| 532 | private volatile int maximumPoolSize; |
| 533 | |
| 534 | /** |
| 535 | * The default rejected execution handler |
| 536 | */ |
| 537 | private static final RejectedExecutionHandler defaultHandler = |
| 538 | new AbortPolicy(); |
| 539 | |
| 540 | /** |
| 541 | * Permission required for callers of shutdown and shutdownNow. |
| 542 | * We additionally require (see checkShutdownAccess) that callers |
| 543 | * have permission to actually interrupt threads in the worker set |
| 544 | * (as governed by Thread.interrupt, which relies on |
| 545 | * ThreadGroup.checkAccess, which in turn relies on |
| 546 | * SecurityManager.checkAccess). Shutdowns are attempted only if |
| 547 | * these checks pass. |
| 548 | * |
| 549 | * All actual invocations of Thread.interrupt (see |
| 550 | * interruptIdleWorkers and interruptWorkers) ignore |
| 551 | * SecurityExceptions, meaning that the attempted interrupts |
| 552 | * silently fail. In the case of shutdown, they should not fail |
| 553 | * unless the SecurityManager has inconsistent policies, sometimes |
| 554 | * allowing access to a thread and sometimes not. In such cases, |
| 555 | * failure to actually interrupt threads may disable or delay full |
| 556 | * termination. Other uses of interruptIdleWorkers are advisory, |
| 557 | * and failure to actually interrupt will merely delay response to |
| 558 | * configuration changes so is not handled exceptionally. |
| 559 | */ |
| 560 | private static final RuntimePermission shutdownPerm = |
| 561 | new RuntimePermission("modifyThread"); |
| 562 | |
| 563 | /** |
| 564 | * Class Worker mainly maintains interrupt control state for |
| 565 | * threads running tasks, along with other minor bookkeeping. |
| 566 | * This class opportunistically extends AbstractQueuedSynchronizer |
| 567 | * to simplify acquiring and releasing a lock surrounding each |
| 568 | * task execution. This protects against interrupts that are |
| 569 | * intended to wake up a worker thread waiting for a task from |
| 570 | * instead interrupting a task being run. We implement a simple |
| 571 | * non-reentrant mutual exclusion lock rather than use ReentrantLock |
| 572 | * because we do not want worker tasks to be able to reacquire the |
| 573 | * lock when they invoke pool control methods like setCorePoolSize. |
| 574 | */ |
| 575 | private final class Worker |
| 576 | extends AbstractQueuedSynchronizer |
| 577 | implements Runnable |
| 578 | { |
| 579 | /** |
| 580 | * This class will never be serialized, but we provide a |
| 581 | * serialVersionUID to suppress a javac warning. |
| 582 | */ |
| 583 | private static final long serialVersionUID = 6138294804551838833L; |
| 584 | |
| 585 | /** Thread this worker is running in. Null if factory fails. */ |
| 586 | final Thread thread; |
| 587 | /** Initial task to run. Possibly null. */ |
| 588 | Runnable firstTask; |
| 589 | /** Per-thread task counter */ |
| 590 | volatile long completedTasks; |
| 591 | |
| 592 | /** |
| 593 | * Creates with given first task and thread from ThreadFactory. |
| 594 | * @param firstTask the first task (null if none) |
| 595 | */ |
| 596 | Worker(Runnable firstTask) { |
| 597 | this.firstTask = firstTask; |
| 598 | this.thread = getThreadFactory().newThread(this); |
| 599 | } |
| 600 | |
| 601 | /** Delegates main run loop to outer runWorker */ |
| 602 | public void run() { |
| 603 | runWorker(this); |
| 604 | } |
| 605 | |
| 606 | // Lock methods |
| 607 | // |
| 608 | // The value 0 represents the unlocked state. |
| 609 | // The value 1 represents the locked state. |
| 610 | |
| 611 | protected boolean isHeldExclusively() { |
| 612 | return getState() == 1; |
| 613 | } |
| 614 | |
| 615 | protected boolean tryAcquire(int unused) { |
| 616 | if (compareAndSetState(0, 1)) { |
| 617 | setExclusiveOwnerThread(Thread.currentThread()); |
| 618 | return true; |
| 619 | } |
| 620 | return false; |
| 621 | } |
| 622 | |
| 623 | protected boolean tryRelease(int unused) { |
| 624 | setExclusiveOwnerThread(null); |
| 625 | setState(0); |
| 626 | return true; |
| 627 | } |
| 628 | |
| 629 | public void lock() { acquire(1); } |
| 630 | public boolean tryLock() { return tryAcquire(1); } |
| 631 | public void unlock() { release(1); } |
| 632 | public boolean isLocked() { return isHeldExclusively(); } |
| 633 | } |
| 634 | |
| 635 | /* |
| 636 | * Methods for setting control state |
| 637 | */ |
| 638 | |
| 639 | /** |
| 640 | * Transitions runState to given target, or leaves it alone if |
| 641 | * already at least the given target. |
| 642 | * |
| 643 | * @param targetState the desired state, either SHUTDOWN or STOP |
| 644 | * (but not TIDYING or TERMINATED -- use tryTerminate for that) |
| 645 | */ |
| 646 | private void advanceRunState(int targetState) { |
| 647 | for (;;) { |
| 648 | int c = ctl.get(); |
| 649 | if (runStateAtLeast(c, targetState) || |
| 650 | ctl.compareAndSet(c, ctlOf(targetState, workerCountOf(c)))) |
| 651 | break; |
| 652 | } |
| 653 | } |
| 654 | |
| 655 | /** |
| 656 | * Transitions to TERMINATED state if either (SHUTDOWN and pool |
| 657 | * and queue empty) or (STOP and pool empty). If otherwise |
| 658 | * eligible to terminate but workerCount is nonzero, interrupts an |
| 659 | * idle worker to ensure that shutdown signals propagate. This |
| 660 | * method must be called following any action that might make |
| 661 | * termination possible -- reducing worker count or removing tasks |
| 662 | * from the queue during shutdown. The method is non-private to |
| 663 | * allow access from ScheduledThreadPoolExecutor. |
| 664 | */ |
| 665 | final void tryTerminate() { |
| 666 | for (;;) { |
| 667 | int c = ctl.get(); |
| 668 | if (isRunning(c) || |
| 669 | runStateAtLeast(c, TIDYING) || |
| 670 | (runStateOf(c) == SHUTDOWN && ! workQueue.isEmpty())) |
| 671 | return; |
| 672 | if (workerCountOf(c) != 0) { // Eligible to terminate |
| 673 | interruptIdleWorkers(ONLY_ONE); |
| 674 | return; |
| 675 | } |
| 676 | |
| 677 | final ReentrantLock mainLock = this.mainLock; |
| 678 | mainLock.lock(); |
| 679 | try { |
| 680 | if (ctl.compareAndSet(c, ctlOf(TIDYING, 0))) { |
| 681 | try { |
| 682 | terminated(); |
| 683 | } finally { |
| 684 | ctl.set(ctlOf(TERMINATED, 0)); |
| 685 | termination.signalAll(); |
| 686 | } |
| 687 | return; |
| 688 | } |
| 689 | } finally { |
| 690 | mainLock.unlock(); |
| 691 | } |
| 692 | // else retry on failed CAS |
| 693 | } |
| 694 | } |
| 695 | |
| 696 | /* |
| 697 | * Methods for controlling interrupts to worker threads. |
| 698 | */ |
| 699 | |
| 700 | /** |
| 701 | * If there is a security manager, makes sure caller has |
| 702 | * permission to shut down threads in general (see shutdownPerm). |
| 703 | * If this passes, additionally makes sure the caller is allowed |
| 704 | * to interrupt each worker thread. This might not be true even if |
| 705 | * first check passed, if the SecurityManager treats some threads |
| 706 | * specially. |
| 707 | */ |
| 708 | private void checkShutdownAccess() { |
| 709 | SecurityManager security = System.getSecurityManager(); |
| 710 | if (security != null) { |
| 711 | security.checkPermission(shutdownPerm); |
| 712 | final ReentrantLock mainLock = this.mainLock; |
| 713 | mainLock.lock(); |
| 714 | try { |
| 715 | for (Worker w : workers) |
| 716 | security.checkAccess(w.thread); |
| 717 | } finally { |
| 718 | mainLock.unlock(); |
| 719 | } |
| 720 | } |
| 721 | } |
| 722 | |
| 723 | /** |
| 724 | * Interrupts all threads, even if active. Ignores SecurityExceptions |
| 725 | * (in which case some threads may remain uninterrupted). |
| 726 | */ |
| 727 | private void interruptWorkers() { |
| 728 | final ReentrantLock mainLock = this.mainLock; |
| 729 | mainLock.lock(); |
| 730 | try { |
| 731 | for (Worker w : workers) { |
| 732 | try { |
| 733 | w.thread.interrupt(); |
| 734 | } catch (SecurityException ignore) { |
| 735 | } |
| 736 | } |
| 737 | } finally { |
| 738 | mainLock.unlock(); |
| 739 | } |
| 740 | } |
| 741 | |
| 742 | /** |
| 743 | * Interrupts threads that might be waiting for tasks (as |
| 744 | * indicated by not being locked) so they can check for |
| 745 | * termination or configuration changes. Ignores |
| 746 | * SecurityExceptions (in which case some threads may remain |
| 747 | * uninterrupted). |
| 748 | * |
| 749 | * @param onlyOne If true, interrupt at most one worker. This is |
| 750 | * called only from tryTerminate when termination is otherwise |
| 751 | * enabled but there are still other workers. In this case, at |
| 752 | * most one waiting worker is interrupted to propagate shutdown |
| 753 | * signals in case all threads are currently waiting. |
| 754 | * Interrupting any arbitrary thread ensures that newly arriving |
| 755 | * workers since shutdown began will also eventually exit. |
| 756 | * To guarantee eventual termination, it suffices to always |
| 757 | * interrupt only one idle worker, but shutdown() interrupts all |
| 758 | * idle workers so that redundant workers exit promptly, not |
| 759 | * waiting for a straggler task to finish. |
| 760 | */ |
| 761 | private void interruptIdleWorkers(boolean onlyOne) { |
| 762 | final ReentrantLock mainLock = this.mainLock; |
| 763 | mainLock.lock(); |
| 764 | try { |
| 765 | for (Worker w : workers) { |
| 766 | Thread t = w.thread; |
| 767 | if (!t.isInterrupted() && w.tryLock()) { |
| 768 | try { |
| 769 | t.interrupt(); |
| 770 | } catch (SecurityException ignore) { |
| 771 | } finally { |
| 772 | w.unlock(); |
| 773 | } |
| 774 | } |
| 775 | if (onlyOne) |
| 776 | break; |
| 777 | } |
| 778 | } finally { |
| 779 | mainLock.unlock(); |
| 780 | } |
| 781 | } |
| 782 | |
| 783 | /** |
| 784 | * Common form of interruptIdleWorkers, to avoid having to |
| 785 | * remember what the boolean argument means. |
| 786 | */ |
| 787 | private void interruptIdleWorkers() { |
| 788 | interruptIdleWorkers(false); |
| 789 | } |
| 790 | |
| 791 | private static final boolean ONLY_ONE = true; |
| 792 | |
| 793 | /** |
| 794 | * Ensures that unless the pool is stopping, the current thread |
| 795 | * does not have its interrupt set. This requires a double-check |
| 796 | * of state in case the interrupt was cleared concurrently with a |
| 797 | * shutdownNow -- if so, the interrupt is re-enabled. |
| 798 | */ |
| 799 | private void clearInterruptsForTaskRun() { |
| 800 | if (runStateLessThan(ctl.get(), STOP) && |
| 801 | Thread.interrupted() && |
| 802 | runStateAtLeast(ctl.get(), STOP)) |
| 803 | Thread.currentThread().interrupt(); |
| 804 | } |
| 805 | |
| 806 | /* |
| 807 | * Misc utilities, most of which are also exported to |
| 808 | * ScheduledThreadPoolExecutor |
| 809 | */ |
| 810 | |
| 811 | /** |
| 812 | * Invokes the rejected execution handler for the given command. |
| 813 | * Package-protected for use by ScheduledThreadPoolExecutor. |
| 814 | */ |
| 815 | final void reject(Runnable command) { |
| 816 | handler.rejectedExecution(command, this); |
| 817 | } |
| 818 | |
| 819 | /** |
| 820 | * Performs any further cleanup following run state transition on |
| 821 | * invocation of shutdown. A no-op here, but used by |
| 822 | * ScheduledThreadPoolExecutor to cancel delayed tasks. |
| 823 | */ |
| 824 | void onShutdown() { |
| 825 | } |
| 826 | |
| 827 | /** |
| 828 | * State check needed by ScheduledThreadPoolExecutor to |
| 829 | * enable running tasks during shutdown. |
| 830 | * |
| 831 | * @param shutdownOK true if should return true if SHUTDOWN |
| 832 | */ |
| 833 | final boolean isRunningOrShutdown(boolean shutdownOK) { |
| 834 | int rs = runStateOf(ctl.get()); |
| 835 | return rs == RUNNING || (rs == SHUTDOWN && shutdownOK); |
| 836 | } |
| 837 | |
| 838 | /** |
| 839 | * Drains the task queue into a new list, normally using |
| 840 | * drainTo. But if the queue is a DelayQueue or any other kind of |
| 841 | * queue for which poll or drainTo may fail to remove some |
| 842 | * elements, it deletes them one by one. |
| 843 | */ |
| 844 | private List<Runnable> drainQueue() { |
| 845 | BlockingQueue<Runnable> q = workQueue; |
| 846 | List<Runnable> taskList = new ArrayList<Runnable>(); |
| 847 | q.drainTo(taskList); |
| 848 | if (!q.isEmpty()) { |
| 849 | for (Runnable r : q.toArray(new Runnable[0])) { |
| 850 | if (q.remove(r)) |
| 851 | taskList.add(r); |
| 852 | } |
| 853 | } |
| 854 | return taskList; |
| 855 | } |
| 856 | |
| 857 | /* |
| 858 | * Methods for creating, running and cleaning up after workers |
| 859 | */ |
| 860 | |
| 861 | /** |
| 862 | * Checks if a new worker can be added with respect to current |
| 863 | * pool state and the given bound (either core or maximum). If so, |
| 864 | * the worker count is adjusted accordingly, and, if possible, a |
| 865 | * new worker is created and started running firstTask as its |
| 866 | * first task. This method returns false if the pool is stopped or |
| 867 | * eligible to shut down. It also returns false if the thread |
| 868 | * factory fails to create a thread when asked, which requires a |
| 869 | * backout of workerCount, and a recheck for termination, in case |
| 870 | * the existence of this worker was holding up termination. |
| 871 | * |
| 872 | * @param firstTask the task the new thread should run first (or |
| 873 | * null if none). Workers are created with an initial first task |
| 874 | * (in method execute()) to bypass queuing when there are fewer |
| 875 | * than corePoolSize threads (in which case we always start one), |
| 876 | * or when the queue is full (in which case we must bypass queue). |
| 877 | * Initially idle threads are usually created via |
| 878 | * prestartCoreThread or to replace other dying workers. |
| 879 | * |
| 880 | * @param core if true use corePoolSize as bound, else |
| 881 | * maximumPoolSize. (A boolean indicator is used here rather than a |
| 882 | * value to ensure reads of fresh values after checking other pool |
| 883 | * state). |
| 884 | * @return true if successful |
| 885 | */ |
| 886 | private boolean addWorker(Runnable firstTask, boolean core) { |
| 887 | retry: |
| 888 | for (;;) { |
| 889 | int c = ctl.get(); |
| 890 | int rs = runStateOf(c); |
| 891 | |
| 892 | // Check if queue empty only if necessary. |
| 893 | if (rs >= SHUTDOWN && |
| 894 | ! (rs == SHUTDOWN && |
| 895 | firstTask == null && |
| 896 | ! workQueue.isEmpty())) |
| 897 | return false; |
| 898 | |
| 899 | for (;;) { |
| 900 | int wc = workerCountOf(c); |
| 901 | if (wc >= CAPACITY || |
| 902 | wc >= (core ? corePoolSize : maximumPoolSize)) |
| 903 | return false; |
| 904 | if (compareAndIncrementWorkerCount(c)) |
| 905 | break retry; |
| 906 | c = ctl.get(); // Re-read ctl |
| 907 | if (runStateOf(c) != rs) |
| 908 | continue retry; |
| 909 | // else CAS failed due to workerCount change; retry inner loop |
| 910 | } |
| 911 | } |
| 912 | |
| 913 | Worker w = new Worker(firstTask); |
| 914 | Thread t = w.thread; |
| 915 | |
| 916 | final ReentrantLock mainLock = this.mainLock; |
| 917 | mainLock.lock(); |
| 918 | try { |
| 919 | // Recheck while holding lock. |
| 920 | // Back out on ThreadFactory failure or if |
| 921 | // shut down before lock acquired. |
| 922 | int c = ctl.get(); |
| 923 | int rs = runStateOf(c); |
| 924 | |
| 925 | if (t == null || |
| 926 | (rs >= SHUTDOWN && |
| 927 | ! (rs == SHUTDOWN && |
| 928 | firstTask == null))) { |
| 929 | decrementWorkerCount(); |
| 930 | tryTerminate(); |
| 931 | return false; |
| 932 | } |
| 933 | |
| 934 | workers.add(w); |
| 935 | |
| 936 | int s = workers.size(); |
| 937 | if (s > largestPoolSize) |
| 938 | largestPoolSize = s; |
| 939 | } finally { |
| 940 | mainLock.unlock(); |
| 941 | } |
| 942 | |
| 943 | t.start(); |
| 944 | // It is possible (but unlikely) for a thread to have been |
| 945 | // added to workers, but not yet started, during transition to |
| 946 | // STOP, which could result in a rare missed interrupt, |
| 947 | // because Thread.interrupt is not guaranteed to have any effect |
| 948 | // on a non-yet-started Thread (see Thread#interrupt). |
| 949 | if (runStateOf(ctl.get()) == STOP && ! t.isInterrupted()) |
| 950 | t.interrupt(); |
| 951 | |
| 952 | return true; |
| 953 | } |
| 954 | |
| 955 | /** |
| 956 | * Performs cleanup and bookkeeping for a dying worker. Called |
| 957 | * only from worker threads. Unless completedAbruptly is set, |
| 958 | * assumes that workerCount has already been adjusted to account |
| 959 | * for exit. This method removes thread from worker set, and |
| 960 | * possibly terminates the pool or replaces the worker if either |
| 961 | * it exited due to user task exception or if fewer than |
| 962 | * corePoolSize workers are running or queue is non-empty but |
| 963 | * there are no workers. |
| 964 | * |
| 965 | * @param w the worker |
| 966 | * @param completedAbruptly if the worker died due to user exception |
| 967 | */ |
| 968 | private void processWorkerExit(Worker w, boolean completedAbruptly) { |
| 969 | if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted |
| 970 | decrementWorkerCount(); |
| 971 | |
| 972 | final ReentrantLock mainLock = this.mainLock; |
| 973 | mainLock.lock(); |
| 974 | try { |
| 975 | completedTaskCount += w.completedTasks; |
| 976 | workers.remove(w); |
| 977 | } finally { |
| 978 | mainLock.unlock(); |
| 979 | } |
| 980 | |
| 981 | tryTerminate(); |
| 982 | |
| 983 | int c = ctl.get(); |
| 984 | if (runStateLessThan(c, STOP)) { |
| 985 | if (!completedAbruptly) { |
| 986 | int min = allowCoreThreadTimeOut ? 0 : corePoolSize; |
| 987 | if (min == 0 && ! workQueue.isEmpty()) |
| 988 | min = 1; |
| 989 | if (workerCountOf(c) >= min) |
| 990 | return; // replacement not needed |
| 991 | } |
| 992 | addWorker(null, false); |
| 993 | } |
| 994 | } |
| 995 | |
| 996 | /** |
| 997 | * Performs blocking or timed wait for a task, depending on |
| 998 | * current configuration settings, or returns null if this worker |
| 999 | * must exit because of any of: |
| 1000 | * 1. There are more than maximumPoolSize workers (due to |
| 1001 | * a call to setMaximumPoolSize). |
| 1002 | * 2. The pool is stopped. |
| 1003 | * 3. The pool is shutdown and the queue is empty. |
| 1004 | * 4. This worker timed out waiting for a task, and timed-out |
| 1005 | * workers are subject to termination (that is, |
| 1006 | * {@code allowCoreThreadTimeOut || workerCount > corePoolSize}) |
| 1007 | * both before and after the timed wait. |
| 1008 | * |
| 1009 | * @return task, or null if the worker must exit, in which case |
| 1010 | * workerCount is decremented |
| 1011 | */ |
| 1012 | private Runnable getTask() { |
| 1013 | boolean timedOut = false; // Did the last poll() time out? |
| 1014 | |
| 1015 | retry: |
| 1016 | for (;;) { |
| 1017 | int c = ctl.get(); |
| 1018 | int rs = runStateOf(c); |
| 1019 | |
| 1020 | // Check if queue empty only if necessary. |
| 1021 | if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) { |
| 1022 | decrementWorkerCount(); |
| 1023 | return null; |
| 1024 | } |
| 1025 | |
| 1026 | boolean timed; // Are workers subject to culling? |
| 1027 | |
| 1028 | for (;;) { |
| 1029 | int wc = workerCountOf(c); |
| 1030 | timed = allowCoreThreadTimeOut || wc > corePoolSize; |
| 1031 | |
| 1032 | if (wc <= maximumPoolSize && ! (timedOut && timed)) |
| 1033 | break; |
| 1034 | if (compareAndDecrementWorkerCount(c)) |
| 1035 | return null; |
| 1036 | c = ctl.get(); // Re-read ctl |
| 1037 | if (runStateOf(c) != rs) |
| 1038 | continue retry; |
| 1039 | // else CAS failed due to workerCount change; retry inner loop |
| 1040 | } |
| 1041 | |
| 1042 | try { |
| 1043 | Runnable r = timed ? |
| 1044 | workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) : |
| 1045 | workQueue.take(); |
| 1046 | if (r != null) |
| 1047 | return r; |
| 1048 | timedOut = true; |
| 1049 | } catch (InterruptedException retry) { |
| 1050 | timedOut = false; |
| 1051 | } |
| 1052 | } |
| 1053 | } |
| 1054 | |
| 1055 | /** |
| 1056 | * Main worker run loop. Repeatedly gets tasks from queue and |
| 1057 | * executes them, while coping with a number of issues: |
| 1058 | * |
| 1059 | * 1. We may start out with an initial task, in which case we |
| 1060 | * don't need to get the first one. Otherwise, as long as pool is |
| 1061 | * running, we get tasks from getTask. If it returns null then the |
| 1062 | * worker exits due to changed pool state or configuration |
| 1063 | * parameters. Other exits result from exception throws in |
| 1064 | * external code, in which case completedAbruptly holds, which |
| 1065 | * usually leads processWorkerExit to replace this thread. |
| 1066 | * |
| 1067 | * 2. Before running any task, the lock is acquired to prevent |
| 1068 | * other pool interrupts while the task is executing, and |
| 1069 | * clearInterruptsForTaskRun called to ensure that unless pool is |
| 1070 | * stopping, this thread does not have its interrupt set. |
| 1071 | * |
| 1072 | * 3. Each task run is preceded by a call to beforeExecute, which |
| 1073 | * might throw an exception, in which case we cause thread to die |
| 1074 | * (breaking loop with completedAbruptly true) without processing |
| 1075 | * the task. |
| 1076 | * |
| 1077 | * 4. Assuming beforeExecute completes normally, we run the task, |
| 1078 | * gathering any of its thrown exceptions to send to |
| 1079 | * afterExecute. We separately handle RuntimeException, Error |
| 1080 | * (both of which the specs guarantee that we trap) and arbitrary |
| 1081 | * Throwables. Because we cannot rethrow Throwables within |
| 1082 | * Runnable.run, we wrap them within Errors on the way out (to the |
| 1083 | * thread's UncaughtExceptionHandler). Any thrown exception also |
| 1084 | * conservatively causes thread to die. |
| 1085 | * |
| 1086 | * 5. After task.run completes, we call afterExecute, which may |
| 1087 | * also throw an exception, which will also cause thread to |
| 1088 | * die. According to JLS Sec 14.20, this exception is the one that |
| 1089 | * will be in effect even if task.run throws. |
| 1090 | * |
| 1091 | * The net effect of the exception mechanics is that afterExecute |
| 1092 | * and the thread's UncaughtExceptionHandler have as accurate |
| 1093 | * information as we can provide about any problems encountered by |
| 1094 | * user code. |
| 1095 | * |
| 1096 | * @param w the worker |
| 1097 | */ |
| 1098 | final void runWorker(Worker w) { |
| 1099 | Runnable task = w.firstTask; |
| 1100 | w.firstTask = null; |
| 1101 | boolean completedAbruptly = true; |
| 1102 | try { |
| 1103 | while (task != null || (task = getTask()) != null) { |
| 1104 | w.lock(); |
| 1105 | clearInterruptsForTaskRun(); |
| 1106 | try { |
| 1107 | beforeExecute(w.thread, task); |
| 1108 | Throwable thrown = null; |
| 1109 | try { |
| 1110 | task.run(); |
| 1111 | } catch (RuntimeException x) { |
| 1112 | thrown = x; throw x; |
| 1113 | } catch (Error x) { |
| 1114 | thrown = x; throw x; |
| 1115 | } catch (Throwable x) { |
| 1116 | thrown = x; throw new Error(x); |
| 1117 | } finally { |
| 1118 | afterExecute(task, thrown); |
| 1119 | } |
| 1120 | } finally { |
| 1121 | task = null; |
| 1122 | w.completedTasks++; |
| 1123 | w.unlock(); |
| 1124 | } |
| 1125 | } |
| 1126 | completedAbruptly = false; |
| 1127 | } finally { |
| 1128 | processWorkerExit(w, completedAbruptly); |
| 1129 | } |
| 1130 | } |
| 1131 | |
| 1132 | // Public constructors and methods |
| 1133 | |
| 1134 | /** |
| 1135 | * Creates a new {@code ThreadPoolExecutor} with the given initial |
| 1136 | * parameters and default thread factory and rejected execution handler. |
| 1137 | * It may be more convenient to use one of the {@link Executors} factory |
| 1138 | * methods instead of this general purpose constructor. |
| 1139 | * |
| 1140 | * @param corePoolSize the number of threads to keep in the pool, even |
| 1141 | * if they are idle, unless {@code allowCoreThreadTimeOut} is set |
| 1142 | * @param maximumPoolSize the maximum number of threads to allow in the |
| 1143 | * pool |
| 1144 | * @param keepAliveTime when the number of threads is greater than |
| 1145 | * the core, this is the maximum time that excess idle threads |
| 1146 | * will wait for new tasks before terminating. |
| 1147 | * @param unit the time unit for the {@code keepAliveTime} argument |
| 1148 | * @param workQueue the queue to use for holding tasks before they are |
| 1149 | * executed. This queue will hold only the {@code Runnable} |
| 1150 | * tasks submitted by the {@code execute} method. |
| 1151 | * @throws IllegalArgumentException if one of the following holds:<br> |
| 1152 | * {@code corePoolSize < 0}<br> |
| 1153 | * {@code keepAliveTime < 0}<br> |
| 1154 | * {@code maximumPoolSize <= 0}<br> |
| 1155 | * {@code maximumPoolSize < corePoolSize} |
| 1156 | * @throws NullPointerException if {@code workQueue} is null |
| 1157 | */ |
| 1158 | public ThreadPoolExecutor(int corePoolSize, |
| 1159 | int maximumPoolSize, |
| 1160 | long keepAliveTime, |
| 1161 | TimeUnit unit, |
| 1162 | BlockingQueue<Runnable> workQueue) { |
| 1163 | this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
| 1164 | Executors.defaultThreadFactory(), defaultHandler); |
| 1165 | } |
| 1166 | |
| 1167 | /** |
| 1168 | * Creates a new {@code ThreadPoolExecutor} with the given initial |
| 1169 | * parameters and default rejected execution handler. |
| 1170 | * |
| 1171 | * @param corePoolSize the number of threads to keep in the pool, even |
| 1172 | * if they are idle, unless {@code allowCoreThreadTimeOut} is set |
| 1173 | * @param maximumPoolSize the maximum number of threads to allow in the |
| 1174 | * pool |
| 1175 | * @param keepAliveTime when the number of threads is greater than |
| 1176 | * the core, this is the maximum time that excess idle threads |
| 1177 | * will wait for new tasks before terminating. |
| 1178 | * @param unit the time unit for the {@code keepAliveTime} argument |
| 1179 | * @param workQueue the queue to use for holding tasks before they are |
| 1180 | * executed. This queue will hold only the {@code Runnable} |
| 1181 | * tasks submitted by the {@code execute} method. |
| 1182 | * @param threadFactory the factory to use when the executor |
| 1183 | * creates a new thread |
| 1184 | * @throws IllegalArgumentException if one of the following holds:<br> |
| 1185 | * {@code corePoolSize < 0}<br> |
| 1186 | * {@code keepAliveTime < 0}<br> |
| 1187 | * {@code maximumPoolSize <= 0}<br> |
| 1188 | * {@code maximumPoolSize < corePoolSize} |
| 1189 | * @throws NullPointerException if {@code workQueue} |
| 1190 | * or {@code threadFactory} is null |
| 1191 | */ |
| 1192 | public ThreadPoolExecutor(int corePoolSize, |
| 1193 | int maximumPoolSize, |
| 1194 | long keepAliveTime, |
| 1195 | TimeUnit unit, |
| 1196 | BlockingQueue<Runnable> workQueue, |
| 1197 | ThreadFactory threadFactory) { |
| 1198 | this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
| 1199 | threadFactory, defaultHandler); |
| 1200 | } |
| 1201 | |
| 1202 | /** |
| 1203 | * Creates a new {@code ThreadPoolExecutor} with the given initial |
| 1204 | * parameters and default thread factory. |
| 1205 | * |
| 1206 | * @param corePoolSize the number of threads to keep in the pool, even |
| 1207 | * if they are idle, unless {@code allowCoreThreadTimeOut} is set |
| 1208 | * @param maximumPoolSize the maximum number of threads to allow in the |
| 1209 | * pool |
| 1210 | * @param keepAliveTime when the number of threads is greater than |
| 1211 | * the core, this is the maximum time that excess idle threads |
| 1212 | * will wait for new tasks before terminating. |
| 1213 | * @param unit the time unit for the {@code keepAliveTime} argument |
| 1214 | * @param workQueue the queue to use for holding tasks before they are |
| 1215 | * executed. This queue will hold only the {@code Runnable} |
| 1216 | * tasks submitted by the {@code execute} method. |
| 1217 | * @param handler the handler to use when execution is blocked |
| 1218 | * because the thread bounds and queue capacities are reached |
| 1219 | * @throws IllegalArgumentException if one of the following holds:<br> |
| 1220 | * {@code corePoolSize < 0}<br> |
| 1221 | * {@code keepAliveTime < 0}<br> |
| 1222 | * {@code maximumPoolSize <= 0}<br> |
| 1223 | * {@code maximumPoolSize < corePoolSize} |
| 1224 | * @throws NullPointerException if {@code workQueue} |
| 1225 | * or {@code handler} is null |
| 1226 | */ |
| 1227 | public ThreadPoolExecutor(int corePoolSize, |
| 1228 | int maximumPoolSize, |
| 1229 | long keepAliveTime, |
| 1230 | TimeUnit unit, |
| 1231 | BlockingQueue<Runnable> workQueue, |
| 1232 | RejectedExecutionHandler handler) { |
| 1233 | this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
| 1234 | Executors.defaultThreadFactory(), handler); |
| 1235 | } |
| 1236 | |
| 1237 | /** |
| 1238 | * Creates a new {@code ThreadPoolExecutor} with the given initial |
| 1239 | * parameters. |
| 1240 | * |
| 1241 | * @param corePoolSize the number of threads to keep in the pool, even |
| 1242 | * if they are idle, unless {@code allowCoreThreadTimeOut} is set |
| 1243 | * @param maximumPoolSize the maximum number of threads to allow in the |
| 1244 | * pool |
| 1245 | * @param keepAliveTime when the number of threads is greater than |
| 1246 | * the core, this is the maximum time that excess idle threads |
| 1247 | * will wait for new tasks before terminating. |
| 1248 | * @param unit the time unit for the {@code keepAliveTime} argument |
| 1249 | * @param workQueue the queue to use for holding tasks before they are |
| 1250 | * executed. This queue will hold only the {@code Runnable} |
| 1251 | * tasks submitted by the {@code execute} method. |
| 1252 | * @param threadFactory the factory to use when the executor |
| 1253 | * creates a new thread |
| 1254 | * @param handler the handler to use when execution is blocked |
| 1255 | * because the thread bounds and queue capacities are reached |
| 1256 | * @throws IllegalArgumentException if one of the following holds:<br> |
| 1257 | * {@code corePoolSize < 0}<br> |
| 1258 | * {@code keepAliveTime < 0}<br> |
| 1259 | * {@code maximumPoolSize <= 0}<br> |
| 1260 | * {@code maximumPoolSize < corePoolSize} |
| 1261 | * @throws NullPointerException if {@code workQueue} |
| 1262 | * or {@code threadFactory} or {@code handler} is null |
| 1263 | */ |
| 1264 | public ThreadPoolExecutor(int corePoolSize, |
| 1265 | int maximumPoolSize, |
| 1266 | long keepAliveTime, |
| 1267 | TimeUnit unit, |
| 1268 | BlockingQueue<Runnable> workQueue, |
| 1269 | ThreadFactory threadFactory, |
| 1270 | RejectedExecutionHandler handler) { |
| 1271 | if (corePoolSize < 0 || |
| 1272 | maximumPoolSize <= 0 || |
| 1273 | maximumPoolSize < corePoolSize || |
| 1274 | keepAliveTime < 0) |
| 1275 | throw new IllegalArgumentException(); |
| 1276 | if (workQueue == null || threadFactory == null || handler == null) |
| 1277 | throw new NullPointerException(); |
| 1278 | this.corePoolSize = corePoolSize; |
| 1279 | this.maximumPoolSize = maximumPoolSize; |
| 1280 | this.workQueue = workQueue; |
| 1281 | this.keepAliveTime = unit.toNanos(keepAliveTime); |
| 1282 | this.threadFactory = threadFactory; |
| 1283 | this.handler = handler; |
| 1284 | } |
| 1285 | |
| 1286 | /** |
| 1287 | * Executes the given task sometime in the future. The task |
| 1288 | * may execute in a new thread or in an existing pooled thread. |
| 1289 | * |
| 1290 | * If the task cannot be submitted for execution, either because this |
| 1291 | * executor has been shutdown or because its capacity has been reached, |
| 1292 | * the task is handled by the current {@code RejectedExecutionHandler}. |
| 1293 | * |
| 1294 | * @param command the task to execute |
| 1295 | * @throws RejectedExecutionException at discretion of |
| 1296 | * {@code RejectedExecutionHandler}, if the task |
| 1297 | * cannot be accepted for execution |
| 1298 | * @throws NullPointerException if {@code command} is null |
| 1299 | */ |
| 1300 | public void execute(Runnable command) { |
| 1301 | if (command == null) |
| 1302 | throw new NullPointerException(); |
| 1303 | /* |
| 1304 | * Proceed in 3 steps: |
| 1305 | * |
| 1306 | * 1. If fewer than corePoolSize threads are running, try to |
| 1307 | * start a new thread with the given command as its first |
| 1308 | * task. The call to addWorker atomically checks runState and |
| 1309 | * workerCount, and so prevents false alarms that would add |
| 1310 | * threads when it shouldn't, by returning false. |
| 1311 | * |
| 1312 | * 2. If a task can be successfully queued, then we still need |
| 1313 | * to double-check whether we should have added a thread |
| 1314 | * (because existing ones died since last checking) or that |
| 1315 | * the pool shut down since entry into this method. So we |
| 1316 | * recheck state and if necessary roll back the enqueuing if |
| 1317 | * stopped, or start a new thread if there are none. |
| 1318 | * |
| 1319 | * 3. If we cannot queue task, then we try to add a new |
| 1320 | * thread. If it fails, we know we are shut down or saturated |
| 1321 | * and so reject the task. |
| 1322 | */ |
| 1323 | int c = ctl.get(); |
| 1324 | if (workerCountOf(c) < corePoolSize) { |
| 1325 | if (addWorker(command, true)) |
| 1326 | return; |
| 1327 | c = ctl.get(); |
| 1328 | } |
| 1329 | if (isRunning(c) && workQueue.offer(command)) { |
| 1330 | int recheck = ctl.get(); |
| 1331 | if (! isRunning(recheck) && remove(command)) |
| 1332 | reject(command); |
| 1333 | else if (workerCountOf(recheck) == 0) |
| 1334 | addWorker(null, false); |
| 1335 | } |
| 1336 | else if (!addWorker(command, false)) |
| 1337 | reject(command); |
| 1338 | } |
| 1339 | |
| 1340 | /** |
| 1341 | * Initiates an orderly shutdown in which previously submitted |
| 1342 | * tasks are executed, but no new tasks will be accepted. |
| 1343 | * Invocation has no additional effect if already shut down. |
| 1344 | * |
| 1345 | * @throws SecurityException {@inheritDoc} |
| 1346 | */ |
| 1347 | public void shutdown() { |
| 1348 | final ReentrantLock mainLock = this.mainLock; |
| 1349 | mainLock.lock(); |
| 1350 | try { |
| 1351 | checkShutdownAccess(); |
| 1352 | advanceRunState(SHUTDOWN); |
| 1353 | interruptIdleWorkers(); |
| 1354 | onShutdown(); // hook for ScheduledThreadPoolExecutor |
| 1355 | } finally { |
| 1356 | mainLock.unlock(); |
| 1357 | } |
| 1358 | tryTerminate(); |
| 1359 | } |
| 1360 | |
| 1361 | /** |
| 1362 | * Attempts to stop all actively executing tasks, halts the |
| 1363 | * processing of waiting tasks, and returns a list of the tasks |
| 1364 | * that were awaiting execution. These tasks are drained (removed) |
| 1365 | * from the task queue upon return from this method. |
| 1366 | * |
| 1367 | * <p>There are no guarantees beyond best-effort attempts to stop |
| 1368 | * processing actively executing tasks. This implementation |
| 1369 | * cancels tasks via {@link Thread#interrupt}, so any task that |
| 1370 | * fails to respond to interrupts may never terminate. |
| 1371 | * |
| 1372 | * @throws SecurityException {@inheritDoc} |
| 1373 | */ |
| 1374 | public List<Runnable> shutdownNow() { |
| 1375 | List<Runnable> tasks; |
| 1376 | final ReentrantLock mainLock = this.mainLock; |
| 1377 | mainLock.lock(); |
| 1378 | try { |
| 1379 | checkShutdownAccess(); |
| 1380 | advanceRunState(STOP); |
| 1381 | interruptWorkers(); |
| 1382 | tasks = drainQueue(); |
| 1383 | } finally { |
| 1384 | mainLock.unlock(); |
| 1385 | } |
| 1386 | tryTerminate(); |
| 1387 | return tasks; |
| 1388 | } |
| 1389 | |
| 1390 | public boolean isShutdown() { |
| 1391 | return ! isRunning(ctl.get()); |
| 1392 | } |
| 1393 | |
| 1394 | /** |
| 1395 | * Returns true if this executor is in the process of terminating |
| 1396 | * after {@link #shutdown} or {@link #shutdownNow} but has not |
| 1397 | * completely terminated. This method may be useful for |
| 1398 | * debugging. A return of {@code true} reported a sufficient |
| 1399 | * period after shutdown may indicate that submitted tasks have |
| 1400 | * ignored or suppressed interruption, causing this executor not |
| 1401 | * to properly terminate. |
| 1402 | * |
| 1403 | * @return true if terminating but not yet terminated |
| 1404 | */ |
| 1405 | public boolean isTerminating() { |
| 1406 | int c = ctl.get(); |
| 1407 | return ! isRunning(c) && runStateLessThan(c, TERMINATED); |
| 1408 | } |
| 1409 | |
| 1410 | public boolean isTerminated() { |
| 1411 | return runStateAtLeast(ctl.get(), TERMINATED); |
| 1412 | } |
| 1413 | |
| 1414 | public boolean awaitTermination(long timeout, TimeUnit unit) |
| 1415 | throws InterruptedException { |
| 1416 | long nanos = unit.toNanos(timeout); |
| 1417 | final ReentrantLock mainLock = this.mainLock; |
| 1418 | mainLock.lock(); |
| 1419 | try { |
| 1420 | for (;;) { |
| 1421 | if (runStateAtLeast(ctl.get(), TERMINATED)) |
| 1422 | return true; |
| 1423 | if (nanos <= 0) |
| 1424 | return false; |
| 1425 | nanos = termination.awaitNanos(nanos); |
| 1426 | } |
| 1427 | } finally { |
| 1428 | mainLock.unlock(); |
| 1429 | } |
| 1430 | } |
| 1431 | |
| 1432 | /** |
| 1433 | * Invokes {@code shutdown} when this executor is no longer |
| 1434 | * referenced and it has no threads. |
| 1435 | */ |
| 1436 | protected void finalize() { |
| 1437 | shutdown(); |
| 1438 | } |
| 1439 | |
| 1440 | /** |
| 1441 | * Sets the thread factory used to create new threads. |
| 1442 | * |
| 1443 | * @param threadFactory the new thread factory |
| 1444 | * @throws NullPointerException if threadFactory is null |
| 1445 | * @see #getThreadFactory |
| 1446 | */ |
| 1447 | public void setThreadFactory(ThreadFactory threadFactory) { |
| 1448 | if (threadFactory == null) |
| 1449 | throw new NullPointerException(); |
| 1450 | this.threadFactory = threadFactory; |
| 1451 | } |
| 1452 | |
| 1453 | /** |
| 1454 | * Returns the thread factory used to create new threads. |
| 1455 | * |
| 1456 | * @return the current thread factory |
| 1457 | * @see #setThreadFactory |
| 1458 | */ |
| 1459 | public ThreadFactory getThreadFactory() { |
| 1460 | return threadFactory; |
| 1461 | } |
| 1462 | |
| 1463 | /** |
| 1464 | * Sets a new handler for unexecutable tasks. |
| 1465 | * |
| 1466 | * @param handler the new handler |
| 1467 | * @throws NullPointerException if handler is null |
| 1468 | * @see #getRejectedExecutionHandler |
| 1469 | */ |
| 1470 | public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
| 1471 | if (handler == null) |
| 1472 | throw new NullPointerException(); |
| 1473 | this.handler = handler; |
| 1474 | } |
| 1475 | |
| 1476 | /** |
| 1477 | * Returns the current handler for unexecutable tasks. |
| 1478 | * |
| 1479 | * @return the current handler |
| 1480 | * @see #setRejectedExecutionHandler |
| 1481 | */ |
| 1482 | public RejectedExecutionHandler getRejectedExecutionHandler() { |
| 1483 | return handler; |
| 1484 | } |
| 1485 | |
| 1486 | /** |
| 1487 | * Sets the core number of threads. This overrides any value set |
| 1488 | * in the constructor. If the new value is smaller than the |
| 1489 | * current value, excess existing threads will be terminated when |
| 1490 | * they next become idle. If larger, new threads will, if needed, |
| 1491 | * be started to execute any queued tasks. |
| 1492 | * |
| 1493 | * @param corePoolSize the new core size |
| 1494 | * @throws IllegalArgumentException if {@code corePoolSize < 0} |
| 1495 | * @see #getCorePoolSize |
| 1496 | */ |
| 1497 | public void setCorePoolSize(int corePoolSize) { |
| 1498 | if (corePoolSize < 0) |
| 1499 | throw new IllegalArgumentException(); |
| 1500 | int delta = corePoolSize - this.corePoolSize; |
| 1501 | this.corePoolSize = corePoolSize; |
| 1502 | if (workerCountOf(ctl.get()) > corePoolSize) |
| 1503 | interruptIdleWorkers(); |
| 1504 | else if (delta > 0) { |
| 1505 | // We don't really know how many new threads are "needed". |
| 1506 | // As a heuristic, prestart enough new workers (up to new |
| 1507 | // core size) to handle the current number of tasks in |
| 1508 | // queue, but stop if queue becomes empty while doing so. |
| 1509 | int k = Math.min(delta, workQueue.size()); |
| 1510 | while (k-- > 0 && addWorker(null, true)) { |
| 1511 | if (workQueue.isEmpty()) |
| 1512 | break; |
| 1513 | } |
| 1514 | } |
| 1515 | } |
| 1516 | |
| 1517 | /** |
| 1518 | * Returns the core number of threads. |
| 1519 | * |
| 1520 | * @return the core number of threads |
| 1521 | * @see #setCorePoolSize |
| 1522 | */ |
| 1523 | public int getCorePoolSize() { |
| 1524 | return corePoolSize; |
| 1525 | } |
| 1526 | |
| 1527 | /** |
| 1528 | * Starts a core thread, causing it to idly wait for work. This |
| 1529 | * overrides the default policy of starting core threads only when |
| 1530 | * new tasks are executed. This method will return {@code false} |
| 1531 | * if all core threads have already been started. |
| 1532 | * |
| 1533 | * @return {@code true} if a thread was started |
| 1534 | */ |
| 1535 | public boolean prestartCoreThread() { |
| 1536 | return workerCountOf(ctl.get()) < corePoolSize && |
| 1537 | addWorker(null, true); |
| 1538 | } |
| 1539 | |
| 1540 | /** |
| 1541 | * Starts all core threads, causing them to idly wait for work. This |
| 1542 | * overrides the default policy of starting core threads only when |
| 1543 | * new tasks are executed. |
| 1544 | * |
| 1545 | * @return the number of threads started |
| 1546 | */ |
| 1547 | public int prestartAllCoreThreads() { |
| 1548 | int n = 0; |
| 1549 | while (addWorker(null, true)) |
| 1550 | ++n; |
| 1551 | return n; |
| 1552 | } |
| 1553 | |
| 1554 | /** |
| 1555 | * Returns true if this pool allows core threads to time out and |
| 1556 | * terminate if no tasks arrive within the keepAlive time, being |
| 1557 | * replaced if needed when new tasks arrive. When true, the same |
| 1558 | * keep-alive policy applying to non-core threads applies also to |
| 1559 | * core threads. When false (the default), core threads are never |
| 1560 | * terminated due to lack of incoming tasks. |
| 1561 | * |
| 1562 | * @return {@code true} if core threads are allowed to time out, |
| 1563 | * else {@code false} |
| 1564 | * |
| 1565 | * @since 1.6 |
| 1566 | */ |
| 1567 | public boolean allowsCoreThreadTimeOut() { |
| 1568 | return allowCoreThreadTimeOut; |
| 1569 | } |
| 1570 | |
| 1571 | /** |
| 1572 | * Sets the policy governing whether core threads may time out and |
| 1573 | * terminate if no tasks arrive within the keep-alive time, being |
| 1574 | * replaced if needed when new tasks arrive. When false, core |
| 1575 | * threads are never terminated due to lack of incoming |
| 1576 | * tasks. When true, the same keep-alive policy applying to |
| 1577 | * non-core threads applies also to core threads. To avoid |
| 1578 | * continual thread replacement, the keep-alive time must be |
| 1579 | * greater than zero when setting {@code true}. This method |
| 1580 | * should in general be called before the pool is actively used. |
| 1581 | * |
| 1582 | * @param value {@code true} if should time out, else {@code false} |
| 1583 | * @throws IllegalArgumentException if value is {@code true} |
| 1584 | * and the current keep-alive time is not greater than zero |
| 1585 | * |
| 1586 | * @since 1.6 |
| 1587 | */ |
| 1588 | public void allowCoreThreadTimeOut(boolean value) { |
| 1589 | if (value && keepAliveTime <= 0) |
| 1590 | throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
| 1591 | if (value != allowCoreThreadTimeOut) { |
| 1592 | allowCoreThreadTimeOut = value; |
| 1593 | if (value) |
| 1594 | interruptIdleWorkers(); |
| 1595 | } |
| 1596 | } |
| 1597 | |
| 1598 | /** |
| 1599 | * Sets the maximum allowed number of threads. This overrides any |
| 1600 | * value set in the constructor. If the new value is smaller than |
| 1601 | * the current value, excess existing threads will be |
| 1602 | * terminated when they next become idle. |
| 1603 | * |
| 1604 | * @param maximumPoolSize the new maximum |
| 1605 | * @throws IllegalArgumentException if the new maximum is |
| 1606 | * less than or equal to zero, or |
| 1607 | * less than the {@linkplain #getCorePoolSize core pool size} |
| 1608 | * @see #getMaximumPoolSize |
| 1609 | */ |
| 1610 | public void setMaximumPoolSize(int maximumPoolSize) { |
| 1611 | if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
| 1612 | throw new IllegalArgumentException(); |
| 1613 | this.maximumPoolSize = maximumPoolSize; |
| 1614 | if (workerCountOf(ctl.get()) > maximumPoolSize) |
| 1615 | interruptIdleWorkers(); |
| 1616 | } |
| 1617 | |
| 1618 | /** |
| 1619 | * Returns the maximum allowed number of threads. |
| 1620 | * |
| 1621 | * @return the maximum allowed number of threads |
| 1622 | * @see #setMaximumPoolSize |
| 1623 | */ |
| 1624 | public int getMaximumPoolSize() { |
| 1625 | return maximumPoolSize; |
| 1626 | } |
| 1627 | |
| 1628 | /** |
| 1629 | * Sets the time limit for which threads may remain idle before |
| 1630 | * being terminated. If there are more than the core number of |
| 1631 | * threads currently in the pool, after waiting this amount of |
| 1632 | * time without processing a task, excess threads will be |
| 1633 | * terminated. This overrides any value set in the constructor. |
| 1634 | * |
| 1635 | * @param time the time to wait. A time value of zero will cause |
| 1636 | * excess threads to terminate immediately after executing tasks. |
| 1637 | * @param unit the time unit of the {@code time} argument |
| 1638 | * @throws IllegalArgumentException if {@code time} less than zero or |
| 1639 | * if {@code time} is zero and {@code allowsCoreThreadTimeOut} |
| 1640 | * @see #getKeepAliveTime |
| 1641 | */ |
| 1642 | public void setKeepAliveTime(long time, TimeUnit unit) { |
| 1643 | if (time < 0) |
| 1644 | throw new IllegalArgumentException(); |
| 1645 | if (time == 0 && allowsCoreThreadTimeOut()) |
| 1646 | throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
| 1647 | long keepAliveTime = unit.toNanos(time); |
| 1648 | long delta = keepAliveTime - this.keepAliveTime; |
| 1649 | this.keepAliveTime = keepAliveTime; |
| 1650 | if (delta < 0) |
| 1651 | interruptIdleWorkers(); |
| 1652 | } |
| 1653 | |
| 1654 | /** |
| 1655 | * Returns the thread keep-alive time, which is the amount of time |
| 1656 | * that threads in excess of the core pool size may remain |
| 1657 | * idle before being terminated. |
| 1658 | * |
| 1659 | * @param unit the desired time unit of the result |
| 1660 | * @return the time limit |
| 1661 | * @see #setKeepAliveTime |
| 1662 | */ |
| 1663 | public long getKeepAliveTime(TimeUnit unit) { |
| 1664 | return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
| 1665 | } |
| 1666 | |
| 1667 | /* User-level queue utilities */ |
| 1668 | |
| 1669 | /** |
| 1670 | * Returns the task queue used by this executor. Access to the |
| 1671 | * task queue is intended primarily for debugging and monitoring. |
| 1672 | * This queue may be in active use. Retrieving the task queue |
| 1673 | * does not prevent queued tasks from executing. |
| 1674 | * |
| 1675 | * @return the task queue |
| 1676 | */ |
| 1677 | public BlockingQueue<Runnable> getQueue() { |
| 1678 | return workQueue; |
| 1679 | } |
| 1680 | |
| 1681 | /** |
| 1682 | * Removes this task from the executor's internal queue if it is |
| 1683 | * present, thus causing it not to be run if it has not already |
| 1684 | * started. |
| 1685 | * |
| 1686 | * <p> This method may be useful as one part of a cancellation |
| 1687 | * scheme. It may fail to remove tasks that have been converted |
| 1688 | * into other forms before being placed on the internal queue. For |
| 1689 | * example, a task entered using {@code submit} might be |
| 1690 | * converted into a form that maintains {@code Future} status. |
| 1691 | * However, in such cases, method {@link #purge} may be used to |
| 1692 | * remove those Futures that have been cancelled. |
| 1693 | * |
| 1694 | * @param task the task to remove |
| 1695 | * @return true if the task was removed |
| 1696 | */ |
| 1697 | public boolean remove(Runnable task) { |
| 1698 | boolean removed = workQueue.remove(task); |
| 1699 | tryTerminate(); // In case SHUTDOWN and now empty |
| 1700 | return removed; |
| 1701 | } |
| 1702 | |
| 1703 | /** |
| 1704 | * Tries to remove from the work queue all {@link Future} |
| 1705 | * tasks that have been cancelled. This method can be useful as a |
| 1706 | * storage reclamation operation, that has no other impact on |
| 1707 | * functionality. Cancelled tasks are never executed, but may |
| 1708 | * accumulate in work queues until worker threads can actively |
| 1709 | * remove them. Invoking this method instead tries to remove them now. |
| 1710 | * However, this method may fail to remove tasks in |
| 1711 | * the presence of interference by other threads. |
| 1712 | */ |
| 1713 | public void purge() { |
| 1714 | final BlockingQueue<Runnable> q = workQueue; |
| 1715 | try { |
| 1716 | Iterator<Runnable> it = q.iterator(); |
| 1717 | while (it.hasNext()) { |
| 1718 | Runnable r = it.next(); |
| 1719 | if (r instanceof Future<?> && ((Future<?>)r).isCancelled()) |
| 1720 | it.remove(); |
| 1721 | } |
| 1722 | } catch (ConcurrentModificationException fallThrough) { |
| 1723 | // Take slow path if we encounter interference during traversal. |
| 1724 | // Make copy for traversal and call remove for cancelled entries. |
| 1725 | // The slow path is more likely to be O(N*N). |
| 1726 | for (Object r : q.toArray()) |
| 1727 | if (r instanceof Future<?> && ((Future<?>)r).isCancelled()) |
| 1728 | q.remove(r); |
| 1729 | } |
| 1730 | |
| 1731 | tryTerminate(); // In case SHUTDOWN and now empty |
| 1732 | } |
| 1733 | |
| 1734 | /* Statistics */ |
| 1735 | |
| 1736 | /** |
| 1737 | * Returns the current number of threads in the pool. |
| 1738 | * |
| 1739 | * @return the number of threads |
| 1740 | */ |
| 1741 | public int getPoolSize() { |
| 1742 | final ReentrantLock mainLock = this.mainLock; |
| 1743 | mainLock.lock(); |
| 1744 | try { |
| 1745 | // Remove rare and surprising possibility of |
| 1746 | // isTerminated() && getPoolSize() > 0 |
| 1747 | return runStateAtLeast(ctl.get(), TIDYING) ? 0 |
| 1748 | : workers.size(); |
| 1749 | } finally { |
| 1750 | mainLock.unlock(); |
| 1751 | } |
| 1752 | } |
| 1753 | |
| 1754 | /** |
| 1755 | * Returns the approximate number of threads that are actively |
| 1756 | * executing tasks. |
| 1757 | * |
| 1758 | * @return the number of threads |
| 1759 | */ |
| 1760 | public int getActiveCount() { |
| 1761 | final ReentrantLock mainLock = this.mainLock; |
| 1762 | mainLock.lock(); |
| 1763 | try { |
| 1764 | int n = 0; |
| 1765 | for (Worker w : workers) |
| 1766 | if (w.isLocked()) |
| 1767 | ++n; |
| 1768 | return n; |
| 1769 | } finally { |
| 1770 | mainLock.unlock(); |
| 1771 | } |
| 1772 | } |
| 1773 | |
| 1774 | /** |
| 1775 | * Returns the largest number of threads that have ever |
| 1776 | * simultaneously been in the pool. |
| 1777 | * |
| 1778 | * @return the number of threads |
| 1779 | */ |
| 1780 | public int getLargestPoolSize() { |
| 1781 | final ReentrantLock mainLock = this.mainLock; |
| 1782 | mainLock.lock(); |
| 1783 | try { |
| 1784 | return largestPoolSize; |
| 1785 | } finally { |
| 1786 | mainLock.unlock(); |
| 1787 | } |
| 1788 | } |
| 1789 | |
| 1790 | /** |
| 1791 | * Returns the approximate total number of tasks that have ever been |
| 1792 | * scheduled for execution. Because the states of tasks and |
| 1793 | * threads may change dynamically during computation, the returned |
| 1794 | * value is only an approximation. |
| 1795 | * |
| 1796 | * @return the number of tasks |
| 1797 | */ |
| 1798 | public long getTaskCount() { |
| 1799 | final ReentrantLock mainLock = this.mainLock; |
| 1800 | mainLock.lock(); |
| 1801 | try { |
| 1802 | long n = completedTaskCount; |
| 1803 | for (Worker w : workers) { |
| 1804 | n += w.completedTasks; |
| 1805 | if (w.isLocked()) |
| 1806 | ++n; |
| 1807 | } |
| 1808 | return n + workQueue.size(); |
| 1809 | } finally { |
| 1810 | mainLock.unlock(); |
| 1811 | } |
| 1812 | } |
| 1813 | |
| 1814 | /** |
| 1815 | * Returns the approximate total number of tasks that have |
| 1816 | * completed execution. Because the states of tasks and threads |
| 1817 | * may change dynamically during computation, the returned value |
| 1818 | * is only an approximation, but one that does not ever decrease |
| 1819 | * across successive calls. |
| 1820 | * |
| 1821 | * @return the number of tasks |
| 1822 | */ |
| 1823 | public long getCompletedTaskCount() { |
| 1824 | final ReentrantLock mainLock = this.mainLock; |
| 1825 | mainLock.lock(); |
| 1826 | try { |
| 1827 | long n = completedTaskCount; |
| 1828 | for (Worker w : workers) |
| 1829 | n += w.completedTasks; |
| 1830 | return n; |
| 1831 | } finally { |
| 1832 | mainLock.unlock(); |
| 1833 | } |
| 1834 | } |
| 1835 | |
| 1836 | /* Extension hooks */ |
| 1837 | |
| 1838 | /** |
| 1839 | * Method invoked prior to executing the given Runnable in the |
| 1840 | * given thread. This method is invoked by thread {@code t} that |
| 1841 | * will execute task {@code r}, and may be used to re-initialize |
| 1842 | * ThreadLocals, or to perform logging. |
| 1843 | * |
| 1844 | * <p>This implementation does nothing, but may be customized in |
| 1845 | * subclasses. Note: To properly nest multiple overridings, subclasses |
| 1846 | * should generally invoke {@code super.beforeExecute} at the end of |
| 1847 | * this method. |
| 1848 | * |
| 1849 | * @param t the thread that will run task {@code r} |
| 1850 | * @param r the task that will be executed |
| 1851 | */ |
| 1852 | protected void beforeExecute(Thread t, Runnable r) { } |
| 1853 | |
| 1854 | /** |
| 1855 | * Method invoked upon completion of execution of the given Runnable. |
| 1856 | * This method is invoked by the thread that executed the task. If |
| 1857 | * non-null, the Throwable is the uncaught {@code RuntimeException} |
| 1858 | * or {@code Error} that caused execution to terminate abruptly. |
| 1859 | * |
| 1860 | * <p>This implementation does nothing, but may be customized in |
| 1861 | * subclasses. Note: To properly nest multiple overridings, subclasses |
| 1862 | * should generally invoke {@code super.afterExecute} at the |
| 1863 | * beginning of this method. |
| 1864 | * |
| 1865 | * <p><b>Note:</b> When actions are enclosed in tasks (such as |
| 1866 | * {@link FutureTask}) either explicitly or via methods such as |
| 1867 | * {@code submit}, these task objects catch and maintain |
| 1868 | * computational exceptions, and so they do not cause abrupt |
| 1869 | * termination, and the internal exceptions are <em>not</em> |
| 1870 | * passed to this method. If you would like to trap both kinds of |
| 1871 | * failures in this method, you can further probe for such cases, |
| 1872 | * as in this sample subclass that prints either the direct cause |
| 1873 | * or the underlying exception if a task has been aborted: |
| 1874 | * |
| 1875 | * <pre> {@code |
| 1876 | * class ExtendedExecutor extends ThreadPoolExecutor { |
| 1877 | * // ... |
| 1878 | * protected void afterExecute(Runnable r, Throwable t) { |
| 1879 | * super.afterExecute(r, t); |
| 1880 | * if (t == null && r instanceof Future<?>) { |
| 1881 | * try { |
| 1882 | * Object result = ((Future<?>) r).get(); |
| 1883 | * } catch (CancellationException ce) { |
| 1884 | * t = ce; |
| 1885 | * } catch (ExecutionException ee) { |
| 1886 | * t = ee.getCause(); |
| 1887 | * } catch (InterruptedException ie) { |
| 1888 | * Thread.currentThread().interrupt(); // ignore/reset |
| 1889 | * } |
| 1890 | * } |
| 1891 | * if (t != null) |
| 1892 | * System.out.println(t); |
| 1893 | * } |
| 1894 | * }}</pre> |
| 1895 | * |
| 1896 | * @param r the runnable that has completed |
| 1897 | * @param t the exception that caused termination, or null if |
| 1898 | * execution completed normally |
| 1899 | */ |
| 1900 | protected void afterExecute(Runnable r, Throwable t) { } |
| 1901 | |
| 1902 | /** |
| 1903 | * Method invoked when the Executor has terminated. Default |
| 1904 | * implementation does nothing. Note: To properly nest multiple |
| 1905 | * overridings, subclasses should generally invoke |
| 1906 | * {@code super.terminated} within this method. |
| 1907 | */ |
| 1908 | protected void terminated() { } |
| 1909 | |
| 1910 | /* Predefined RejectedExecutionHandlers */ |
| 1911 | |
| 1912 | /** |
| 1913 | * A handler for rejected tasks that runs the rejected task |
| 1914 | * directly in the calling thread of the {@code execute} method, |
| 1915 | * unless the executor has been shut down, in which case the task |
| 1916 | * is discarded. |
| 1917 | */ |
| 1918 | public static class CallerRunsPolicy implements RejectedExecutionHandler { |
| 1919 | /** |
| 1920 | * Creates a {@code CallerRunsPolicy}. |
| 1921 | */ |
| 1922 | public CallerRunsPolicy() { } |
| 1923 | |
| 1924 | /** |
| 1925 | * Executes task r in the caller's thread, unless the executor |
| 1926 | * has been shut down, in which case the task is discarded. |
| 1927 | * |
| 1928 | * @param r the runnable task requested to be executed |
| 1929 | * @param e the executor attempting to execute this task |
| 1930 | */ |
| 1931 | public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
| 1932 | if (!e.isShutdown()) { |
| 1933 | r.run(); |
| 1934 | } |
| 1935 | } |
| 1936 | } |
| 1937 | |
| 1938 | /** |
| 1939 | * A handler for rejected tasks that throws a |
| 1940 | * {@code RejectedExecutionException}. |
| 1941 | */ |
| 1942 | public static class AbortPolicy implements RejectedExecutionHandler { |
| 1943 | /** |
| 1944 | * Creates an {@code AbortPolicy}. |
| 1945 | */ |
| 1946 | public AbortPolicy() { } |
| 1947 | |
| 1948 | /** |
| 1949 | * Always throws RejectedExecutionException. |
| 1950 | * |
| 1951 | * @param r the runnable task requested to be executed |
| 1952 | * @param e the executor attempting to execute this task |
| 1953 | * @throws RejectedExecutionException always. |
| 1954 | */ |
| 1955 | public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
| 1956 | throw new RejectedExecutionException(); |
| 1957 | } |
| 1958 | } |
| 1959 | |
| 1960 | /** |
| 1961 | * A handler for rejected tasks that silently discards the |
| 1962 | * rejected task. |
| 1963 | */ |
| 1964 | public static class DiscardPolicy implements RejectedExecutionHandler { |
| 1965 | /** |
| 1966 | * Creates a {@code DiscardPolicy}. |
| 1967 | */ |
| 1968 | public DiscardPolicy() { } |
| 1969 | |
| 1970 | /** |
| 1971 | * Does nothing, which has the effect of discarding task r. |
| 1972 | * |
| 1973 | * @param r the runnable task requested to be executed |
| 1974 | * @param e the executor attempting to execute this task |
| 1975 | */ |
| 1976 | public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
| 1977 | } |
| 1978 | } |
| 1979 | |
| 1980 | /** |
| 1981 | * A handler for rejected tasks that discards the oldest unhandled |
| 1982 | * request and then retries {@code execute}, unless the executor |
| 1983 | * is shut down, in which case the task is discarded. |
| 1984 | */ |
| 1985 | public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
| 1986 | /** |
| 1987 | * Creates a {@code DiscardOldestPolicy} for the given executor. |
| 1988 | */ |
| 1989 | public DiscardOldestPolicy() { } |
| 1990 | |
| 1991 | /** |
| 1992 | * Obtains and ignores the next task that the executor |
| 1993 | * would otherwise execute, if one is immediately available, |
| 1994 | * and then retries execution of task r, unless the executor |
| 1995 | * is shut down, in which case task r is instead discarded. |
| 1996 | * |
| 1997 | * @param r the runnable task requested to be executed |
| 1998 | * @param e the executor attempting to execute this task |
| 1999 | */ |
| 2000 | public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
| 2001 | if (!e.isShutdown()) { |
| 2002 | e.getQueue().poll(); |
| 2003 | e.execute(r); |
| 2004 | } |
| 2005 | } |
| 2006 | } |
| 2007 | } |