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| 1 | /* | ||
| 2 | * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | import java.util.Date; | ||
| 28 | import java.util.concurrent.atomic.AtomicInteger; | ||
| 29 | |||
| 30 | /** | ||
| 31 | * A facility for threads to schedule tasks for future execution in a | ||
| 32 | * background thread. Tasks may be scheduled for one-time execution, or for | ||
| 33 | * repeated execution at regular intervals. | ||
| 34 | * | ||
| 35 | * <p>Corresponding to each <tt>Timer</tt> object is a single background | ||
| 36 | * thread that is used to execute all of the timer's tasks, sequentially. | ||
| 37 | * Timer tasks should complete quickly. If a timer task takes excessive time | ||
| 38 | * to complete, it "hogs" the timer's task execution thread. This can, in | ||
| 39 | * turn, delay the execution of subsequent tasks, which may "bunch up" and | ||
| 40 | * execute in rapid succession when (and if) the offending task finally | ||
| 41 | * completes. | ||
| 42 | * | ||
| 43 | * <p>After the last live reference to a <tt>Timer</tt> object goes away | ||
| 44 | * <i>and</i> all outstanding tasks have completed execution, the timer's task | ||
| 45 | * execution thread terminates gracefully (and becomes subject to garbage | ||
| 46 | * collection). However, this can take arbitrarily long to occur. By | ||
| 47 | * default, the task execution thread does not run as a <i>daemon thread</i>, | ||
| 48 | * so it is capable of keeping an application from terminating. If a caller | ||
| 49 | * wants to terminate a timer's task execution thread rapidly, the caller | ||
| 50 | * should invoke the timer's <tt>cancel</tt> method. | ||
| 51 | * | ||
| 52 | * <p>If the timer's task execution thread terminates unexpectedly, for | ||
| 53 | * example, because its <tt>stop</tt> method is invoked, any further | ||
| 54 | * attempt to schedule a task on the timer will result in an | ||
| 55 | * <tt>IllegalStateException</tt>, as if the timer's <tt>cancel</tt> | ||
| 56 | * method had been invoked. | ||
| 57 | * | ||
| 58 | * <p>This class is thread-safe: multiple threads can share a single | ||
| 59 | * <tt>Timer</tt> object without the need for external synchronization. | ||
| 60 | * | ||
| 61 | * <p>This class does <i>not</i> offer real-time guarantees: it schedules | ||
| 62 | * tasks using the <tt>Object.wait(long)</tt> method. | ||
| 63 | * | ||
| 64 | * <p>Java 5.0 introduced the {@code java.util.concurrent} package and | ||
| 65 | * one of the concurrency utilities therein is the {@link | ||
| 66 | * java.util.concurrent.ScheduledThreadPoolExecutor | ||
| 67 | * ScheduledThreadPoolExecutor} which is a thread pool for repeatedly | ||
| 68 | * executing tasks at a given rate or delay. It is effectively a more | ||
| 69 | * versatile replacement for the {@code Timer}/{@code TimerTask} | ||
| 70 | * combination, as it allows multiple service threads, accepts various | ||
| 71 | * time units, and doesn't require subclassing {@code TimerTask} (just | ||
| 72 | * implement {@code Runnable}). Configuring {@code | ||
| 73 | * ScheduledThreadPoolExecutor} with one thread makes it equivalent to | ||
| 74 | * {@code Timer}. | ||
| 75 | * | ||
| 76 | * <p>Implementation note: This class scales to large numbers of concurrently | ||
| 77 | * scheduled tasks (thousands should present no problem). Internally, | ||
| 78 | * it uses a binary heap to represent its task queue, so the cost to schedule | ||
| 79 | * a task is O(log n), where n is the number of concurrently scheduled tasks. | ||
| 80 | * | ||
| 81 | * <p>Implementation note: All constructors start a timer thread. | ||
| 82 | * | ||
| 83 | * @author Josh Bloch | ||
| 84 | * @see TimerTask | ||
| 85 | * @see Object#wait(long) | ||
| 86 | * @since 1.3 | ||
| 87 | */ | ||
| 88 | |||
| 89 | public class Timer { | ||
| 90 | /** | ||
| 91 | * The timer task queue. This data structure is shared with the timer | ||
| 92 | * thread. The timer produces tasks, via its various schedule calls, | ||
| 93 | * and the timer thread consumes, executing timer tasks as appropriate, | ||
| 94 | * and removing them from the queue when they're obsolete. | ||
| 95 | */ | ||
| 96 | private final TaskQueue queue = new TaskQueue(); | ||
| 97 | |||
| 98 | /** | ||
| 99 | * The timer thread. | ||
| 100 | */ | ||
| 101 | private final TimerThread thread = new TimerThread(queue); | ||
| 102 | |||
| 103 | /** | ||
| 104 | * This object causes the timer's task execution thread to exit | ||
| 105 | * gracefully when there are no live references to the Timer object and no | ||
| 106 | * tasks in the timer queue. It is used in preference to a finalizer on | ||
| 107 | * Timer as such a finalizer would be susceptible to a subclass's | ||
| 108 | * finalizer forgetting to call it. | ||
| 109 | */ | ||
| 110 | private final Object threadReaper = new Object() { | ||
| 111 | protected void finalize() throws Throwable { | ||
| 112 | synchronized(queue) { | ||
| 113 | thread.newTasksMayBeScheduled = false; | ||
| 114 | queue.notify(); // In case queue is empty. | ||
| 115 | } | ||
| 116 | } | ||
| 117 | }; | ||
| 118 | |||
| 119 | /** | ||
| 120 | * This ID is used to generate thread names. | ||
| 121 | */ | ||
| 122 | private final static AtomicInteger nextSerialNumber = new AtomicInteger(0); | ||
| 123 | private static int serialNumber() { | ||
| 124 | return nextSerialNumber.getAndIncrement(); | ||
| 125 | } | ||
| 126 | |||
| 127 | /** | ||
| 128 | * Creates a new timer. The associated thread does <i>not</i> | ||
| 129 | * {@linkplain Thread#setDaemon run as a daemon}. | ||
| 130 | */ | ||
| 131 | public Timer() { | ||
| 132 | this("Timer-" + serialNumber()); | ||
| 133 | } | ||
| 134 | |||
| 135 | /** | ||
| 136 | * Creates a new timer whose associated thread may be specified to | ||
| 137 | * {@linkplain Thread#setDaemon run as a daemon}. | ||
| 138 | * A daemon thread is called for if the timer will be used to | ||
| 139 | * schedule repeating "maintenance activities", which must be | ||
| 140 | * performed as long as the application is running, but should not | ||
| 141 | * prolong the lifetime of the application. | ||
| 142 | * | ||
| 143 | * @param isDaemon true if the associated thread should run as a daemon. | ||
| 144 | */ | ||
| 145 | public Timer(boolean isDaemon) { | ||
| 146 | this("Timer-" + serialNumber(), isDaemon); | ||
| 147 | } | ||
| 148 | |||
| 149 | /** | ||
| 150 | * Creates a new timer whose associated thread has the specified name. | ||
| 151 | * The associated thread does <i>not</i> | ||
| 152 | * {@linkplain Thread#setDaemon run as a daemon}. | ||
| 153 | * | ||
| 154 | * @param name the name of the associated thread | ||
| 155 | * @throws NullPointerException if {@code name} is null | ||
| 156 | * @since 1.5 | ||
| 157 | */ | ||
| 158 | public Timer(String name) { | ||
| 159 | thread.setName(name); | ||
| 160 | thread.start(); | ||
| 161 | } | ||
| 162 | |||
| 163 | /** | ||
| 164 | * Creates a new timer whose associated thread has the specified name, | ||
| 165 | * and may be specified to | ||
| 166 | * {@linkplain Thread#setDaemon run as a daemon}. | ||
| 167 | * | ||
| 168 | * @param name the name of the associated thread | ||
| 169 | * @param isDaemon true if the associated thread should run as a daemon | ||
| 170 | * @throws NullPointerException if {@code name} is null | ||
| 171 | * @since 1.5 | ||
| 172 | */ | ||
| 173 | public Timer(String name, boolean isDaemon) { | ||
| 174 | thread.setName(name); | ||
| 175 | thread.setDaemon(isDaemon); | ||
| 176 | thread.start(); | ||
| 177 | } | ||
| 178 | |||
| 179 | /** | ||
| 180 | * Schedules the specified task for execution after the specified delay. | ||
| 181 | * | ||
| 182 | * @param task task to be scheduled. | ||
| 183 | * @param delay delay in milliseconds before task is to be executed. | ||
| 184 | * @throws IllegalArgumentException if <tt>delay</tt> is negative, or | ||
| 185 | * <tt>delay + System.currentTimeMillis()</tt> is negative. | ||
| 186 | * @throws IllegalStateException if task was already scheduled or | ||
| 187 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 188 | * @throws NullPointerException if {@code task} is null | ||
| 189 | */ | ||
| 190 | public void schedule(TimerTask task, long delay) { | ||
| 191 | if (delay < 0) | ||
| 192 | throw new IllegalArgumentException("Negative delay."); | ||
| 193 | sched(task, System.currentTimeMillis()+delay, 0); | ||
| 194 | } | ||
| 195 | |||
| 196 | /** | ||
| 197 | * Schedules the specified task for execution at the specified time. If | ||
| 198 | * the time is in the past, the task is scheduled for immediate execution. | ||
| 199 | * | ||
| 200 | * @param task task to be scheduled. | ||
| 201 | * @param time time at which task is to be executed. | ||
| 202 | * @throws IllegalArgumentException if <tt>time.getTime()</tt> is negative. | ||
| 203 | * @throws IllegalStateException if task was already scheduled or | ||
| 204 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 205 | * @throws NullPointerException if {@code task} or {@code time} is null | ||
| 206 | */ | ||
| 207 | public void schedule(TimerTask task, Date time) { | ||
| 208 | sched(task, time.getTime(), 0); | ||
| 209 | } | ||
| 210 | |||
| 211 | /** | ||
| 212 | * Schedules the specified task for repeated <i>fixed-delay execution</i>, | ||
| 213 | * beginning after the specified delay. Subsequent executions take place | ||
| 214 | * at approximately regular intervals separated by the specified period. | ||
| 215 | * | ||
| 216 | * <p>In fixed-delay execution, each execution is scheduled relative to | ||
| 217 | * the actual execution time of the previous execution. If an execution | ||
| 218 | * is delayed for any reason (such as garbage collection or other | ||
| 219 | * background activity), subsequent executions will be delayed as well. | ||
| 220 | * In the long run, the frequency of execution will generally be slightly | ||
| 221 | * lower than the reciprocal of the specified period (assuming the system | ||
| 222 | * clock underlying <tt>Object.wait(long)</tt> is accurate). | ||
| 223 | * | ||
| 224 | * <p>Fixed-delay execution is appropriate for recurring activities | ||
| 225 | * that require "smoothness." In other words, it is appropriate for | ||
| 226 | * activities where it is more important to keep the frequency accurate | ||
| 227 | * in the short run than in the long run. This includes most animation | ||
| 228 | * tasks, such as blinking a cursor at regular intervals. It also includes | ||
| 229 | * tasks wherein regular activity is performed in response to human | ||
| 230 | * input, such as automatically repeating a character as long as a key | ||
| 231 | * is held down. | ||
| 232 | * | ||
| 233 | * @param task task to be scheduled. | ||
| 234 | * @param delay delay in milliseconds before task is to be executed. | ||
| 235 | * @param period time in milliseconds between successive task executions. | ||
| 236 | * @throws IllegalArgumentException if {@code delay < 0}, or | ||
| 237 | * {@code delay + System.currentTimeMillis() < 0}, or | ||
| 238 | * {@code period <= 0} | ||
| 239 | * @throws IllegalStateException if task was already scheduled or | ||
| 240 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 241 | * @throws NullPointerException if {@code task} is null | ||
| 242 | */ | ||
| 243 | public void schedule(TimerTask task, long delay, long period) { | ||
| 244 | if (delay < 0) | ||
| 245 | throw new IllegalArgumentException("Negative delay."); | ||
| 246 | if (period <= 0) | ||
| 247 | throw new IllegalArgumentException("Non-positive period."); | ||
| 248 | sched(task, System.currentTimeMillis()+delay, -period); | ||
| 249 | } | ||
| 250 | |||
| 251 | /** | ||
| 252 | * Schedules the specified task for repeated <i>fixed-delay execution</i>, | ||
| 253 | * beginning at the specified time. Subsequent executions take place at | ||
| 254 | * approximately regular intervals, separated by the specified period. | ||
| 255 | * | ||
| 256 | * <p>In fixed-delay execution, each execution is scheduled relative to | ||
| 257 | * the actual execution time of the previous execution. If an execution | ||
| 258 | * is delayed for any reason (such as garbage collection or other | ||
| 259 | * background activity), subsequent executions will be delayed as well. | ||
| 260 | * In the long run, the frequency of execution will generally be slightly | ||
| 261 | * lower than the reciprocal of the specified period (assuming the system | ||
| 262 | * clock underlying <tt>Object.wait(long)</tt> is accurate). As a | ||
| 263 | * consequence of the above, if the scheduled first time is in the past, | ||
| 264 | * it is scheduled for immediate execution. | ||
| 265 | * | ||
| 266 | * <p>Fixed-delay execution is appropriate for recurring activities | ||
| 267 | * that require "smoothness." In other words, it is appropriate for | ||
| 268 | * activities where it is more important to keep the frequency accurate | ||
| 269 | * in the short run than in the long run. This includes most animation | ||
| 270 | * tasks, such as blinking a cursor at regular intervals. It also includes | ||
| 271 | * tasks wherein regular activity is performed in response to human | ||
| 272 | * input, such as automatically repeating a character as long as a key | ||
| 273 | * is held down. | ||
| 274 | * | ||
| 275 | * @param task task to be scheduled. | ||
| 276 | * @param firstTime First time at which task is to be executed. | ||
| 277 | * @param period time in milliseconds between successive task executions. | ||
| 278 | * @throws IllegalArgumentException if {@code firstTime.getTime() < 0}, or | ||
| 279 | * {@code period <= 0} | ||
| 280 | * @throws IllegalStateException if task was already scheduled or | ||
| 281 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 282 | * @throws NullPointerException if {@code task} or {@code firstTime} is null | ||
| 283 | */ | ||
| 284 | public void schedule(TimerTask task, Date firstTime, long period) { | ||
| 285 | if (period <= 0) | ||
| 286 | throw new IllegalArgumentException("Non-positive period."); | ||
| 287 | sched(task, firstTime.getTime(), -period); | ||
| 288 | } | ||
| 289 | |||
| 290 | /** | ||
| 291 | * Schedules the specified task for repeated <i>fixed-rate execution</i>, | ||
| 292 | * beginning after the specified delay. Subsequent executions take place | ||
| 293 | * at approximately regular intervals, separated by the specified period. | ||
| 294 | * | ||
| 295 | * <p>In fixed-rate execution, each execution is scheduled relative to the | ||
| 296 | * scheduled execution time of the initial execution. If an execution is | ||
| 297 | * delayed for any reason (such as garbage collection or other background | ||
| 298 | * activity), two or more executions will occur in rapid succession to | ||
| 299 | * "catch up." In the long run, the frequency of execution will be | ||
| 300 | * exactly the reciprocal of the specified period (assuming the system | ||
| 301 | * clock underlying <tt>Object.wait(long)</tt> is accurate). | ||
| 302 | * | ||
| 303 | * <p>Fixed-rate execution is appropriate for recurring activities that | ||
| 304 | * are sensitive to <i>absolute</i> time, such as ringing a chime every | ||
| 305 | * hour on the hour, or running scheduled maintenance every day at a | ||
| 306 | * particular time. It is also appropriate for recurring activities | ||
| 307 | * where the total time to perform a fixed number of executions is | ||
| 308 | * important, such as a countdown timer that ticks once every second for | ||
| 309 | * ten seconds. Finally, fixed-rate execution is appropriate for | ||
| 310 | * scheduling multiple repeating timer tasks that must remain synchronized | ||
| 311 | * with respect to one another. | ||
| 312 | * | ||
| 313 | * @param task task to be scheduled. | ||
| 314 | * @param delay delay in milliseconds before task is to be executed. | ||
| 315 | * @param period time in milliseconds between successive task executions. | ||
| 316 | * @throws IllegalArgumentException if {@code delay < 0}, or | ||
| 317 | * {@code delay + System.currentTimeMillis() < 0}, or | ||
| 318 | * {@code period <= 0} | ||
| 319 | * @throws IllegalStateException if task was already scheduled or | ||
| 320 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 321 | * @throws NullPointerException if {@code task} is null | ||
| 322 | */ | ||
| 323 | public void scheduleAtFixedRate(TimerTask task, long delay, long period) { | ||
| 324 | if (delay < 0) | ||
| 325 | throw new IllegalArgumentException("Negative delay."); | ||
| 326 | if (period <= 0) | ||
| 327 | throw new IllegalArgumentException("Non-positive period."); | ||
| 328 | sched(task, System.currentTimeMillis()+delay, period); | ||
| 329 | } | ||
| 330 | |||
| 331 | /** | ||
| 332 | * Schedules the specified task for repeated <i>fixed-rate execution</i>, | ||
| 333 | * beginning at the specified time. Subsequent executions take place at | ||
| 334 | * approximately regular intervals, separated by the specified period. | ||
| 335 | * | ||
| 336 | * <p>In fixed-rate execution, each execution is scheduled relative to the | ||
| 337 | * scheduled execution time of the initial execution. If an execution is | ||
| 338 | * delayed for any reason (such as garbage collection or other background | ||
| 339 | * activity), two or more executions will occur in rapid succession to | ||
| 340 | * "catch up." In the long run, the frequency of execution will be | ||
| 341 | * exactly the reciprocal of the specified period (assuming the system | ||
| 342 | * clock underlying <tt>Object.wait(long)</tt> is accurate). As a | ||
| 343 | * consequence of the above, if the scheduled first time is in the past, | ||
| 344 | * then any "missed" executions will be scheduled for immediate "catch up" | ||
| 345 | * execution. | ||
| 346 | * | ||
| 347 | * <p>Fixed-rate execution is appropriate for recurring activities that | ||
| 348 | * are sensitive to <i>absolute</i> time, such as ringing a chime every | ||
| 349 | * hour on the hour, or running scheduled maintenance every day at a | ||
| 350 | * particular time. It is also appropriate for recurring activities | ||
| 351 | * where the total time to perform a fixed number of executions is | ||
| 352 | * important, such as a countdown timer that ticks once every second for | ||
| 353 | * ten seconds. Finally, fixed-rate execution is appropriate for | ||
| 354 | * scheduling multiple repeating timer tasks that must remain synchronized | ||
| 355 | * with respect to one another. | ||
| 356 | * | ||
| 357 | * @param task task to be scheduled. | ||
| 358 | * @param firstTime First time at which task is to be executed. | ||
| 359 | * @param period time in milliseconds between successive task executions. | ||
| 360 | * @throws IllegalArgumentException if {@code firstTime.getTime() < 0} or | ||
| 361 | * {@code period <= 0} | ||
| 362 | * @throws IllegalStateException if task was already scheduled or | ||
| 363 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 364 | * @throws NullPointerException if {@code task} or {@code firstTime} is null | ||
| 365 | */ | ||
| 366 | public void scheduleAtFixedRate(TimerTask task, Date firstTime, | ||
| 367 | long period) { | ||
| 368 | if (period <= 0) | ||
| 369 | throw new IllegalArgumentException("Non-positive period."); | ||
| 370 | sched(task, firstTime.getTime(), period); | ||
| 371 | } | ||
| 372 | |||
| 373 | /** | ||
| 374 | * Schedule the specified timer task for execution at the specified | ||
| 375 | * time with the specified period, in milliseconds. If period is | ||
| 376 | * positive, the task is scheduled for repeated execution; if period is | ||
| 377 | * zero, the task is scheduled for one-time execution. Time is specified | ||
| 378 | * in Date.getTime() format. This method checks timer state, task state, | ||
| 379 | * and initial execution time, but not period. | ||
| 380 | * | ||
| 381 | * @throws IllegalArgumentException if <tt>time</tt> is negative. | ||
| 382 | * @throws IllegalStateException if task was already scheduled or | ||
| 383 | * cancelled, timer was cancelled, or timer thread terminated. | ||
| 384 | * @throws NullPointerException if {@code task} is null | ||
| 385 | */ | ||
| 386 | private void sched(TimerTask task, long time, long period) { | ||
| 387 | if (time < 0) | ||
| 388 | throw new IllegalArgumentException("Illegal execution time."); | ||
| 389 | |||
| 390 | // Constrain value of period sufficiently to prevent numeric | ||
| 391 | // overflow while still being effectively infinitely large. | ||
| 392 | if (Math.abs(period) > (Long.MAX_VALUE >> 1)) | ||
| 393 | period >>= 1; | ||
| 394 | |||
| 395 | synchronized(queue) { | ||
| 396 | if (!thread.newTasksMayBeScheduled) | ||
| 397 | throw new IllegalStateException("Timer already cancelled."); | ||
| 398 | |||
| 399 | synchronized(task.lock) { | ||
| 400 | if (task.state != TimerTask.VIRGIN) | ||
| 401 | throw new IllegalStateException( | ||
| 402 | "Task already scheduled or cancelled"); | ||
| 403 | task.nextExecutionTime = time; | ||
| 404 | task.period = period; | ||
| 405 | task.state = TimerTask.SCHEDULED; | ||
| 406 | } | ||
| 407 | |||
| 408 | queue.add(task); | ||
| 409 | if (queue.getMin() == task) | ||
| 410 | queue.notify(); | ||
| 411 | } | ||
| 412 | } | ||
| 413 | |||
| 414 | /** | ||
| 415 | * Terminates this timer, discarding any currently scheduled tasks. | ||
| 416 | * Does not interfere with a currently executing task (if it exists). | ||
| 417 | * Once a timer has been terminated, its execution thread terminates | ||
| 418 | * gracefully, and no more tasks may be scheduled on it. | ||
| 419 | * | ||
| 420 | * <p>Note that calling this method from within the run method of a | ||
| 421 | * timer task that was invoked by this timer absolutely guarantees that | ||
| 422 | * the ongoing task execution is the last task execution that will ever | ||
| 423 | * be performed by this timer. | ||
| 424 | * | ||
| 425 | * <p>This method may be called repeatedly; the second and subsequent | ||
| 426 | * calls have no effect. | ||
| 427 | */ | ||
| 428 | public void cancel() { | ||
| 429 | synchronized(queue) { | ||
| 430 | thread.newTasksMayBeScheduled = false; | ||
| 431 | queue.clear(); | ||
| 432 | queue.notify(); // In case queue was already empty. | ||
| 433 | } | ||
| 434 | } | ||
| 435 | |||
| 436 | /** | ||
| 437 | * Removes all cancelled tasks from this timer's task queue. <i>Calling | ||
| 438 | * this method has no effect on the behavior of the timer</i>, but | ||
| 439 | * eliminates the references to the cancelled tasks from the queue. | ||
| 440 | * If there are no external references to these tasks, they become | ||
| 441 | * eligible for garbage collection. | ||
| 442 | * | ||
| 443 | * <p>Most programs will have no need to call this method. | ||
| 444 | * It is designed for use by the rare application that cancels a large | ||
| 445 | * number of tasks. Calling this method trades time for space: the | ||
| 446 | * runtime of the method may be proportional to n + c log n, where n | ||
| 447 | * is the number of tasks in the queue and c is the number of cancelled | ||
| 448 | * tasks. | ||
| 449 | * | ||
| 450 | * <p>Note that it is permissible to call this method from within a | ||
| 451 | * a task scheduled on this timer. | ||
| 452 | * | ||
| 453 | * @return the number of tasks removed from the queue. | ||
| 454 | * @since 1.5 | ||
| 455 | */ | ||
| 456 | public int purge() { | ||
| 457 | int result = 0; | ||
| 458 | |||
| 459 | synchronized(queue) { | ||
| 460 | for (int i = queue.size(); i > 0; i--) { | ||
| 461 | if (queue.get(i).state == TimerTask.CANCELLED) { | ||
| 462 | queue.quickRemove(i); | ||
| 463 | result++; | ||
| 464 | } | ||
| 465 | } | ||
| 466 | |||
| 467 | if (result != 0) | ||
| 468 | queue.heapify(); | ||
| 469 | } | ||
| 470 | |||
| 471 | return result; | ||
| 472 | } | ||
| 473 | } | ||
| 474 | |||
| 475 | /** | ||
| 476 | * This "helper class" implements the timer's task execution thread, which | ||
| 477 | * waits for tasks on the timer queue, executions them when they fire, | ||
| 478 | * reschedules repeating tasks, and removes cancelled tasks and spent | ||
| 479 | * non-repeating tasks from the queue. | ||
| 480 | */ | ||
| 481 | class TimerThread extends Thread { | ||
| 482 | /** | ||
| 483 | * This flag is set to false by the reaper to inform us that there | ||
| 484 | * are no more live references to our Timer object. Once this flag | ||
| 485 | * is true and there are no more tasks in our queue, there is no | ||
| 486 | * work left for us to do, so we terminate gracefully. Note that | ||
| 487 | * this field is protected by queue's monitor! | ||
| 488 | */ | ||
| 489 | boolean newTasksMayBeScheduled = true; | ||
| 490 | |||
| 491 | /** | ||
| 492 | * Our Timer's queue. We store this reference in preference to | ||
| 493 | * a reference to the Timer so the reference graph remains acyclic. | ||
| 494 | * Otherwise, the Timer would never be garbage-collected and this | ||
| 495 | * thread would never go away. | ||
| 496 | */ | ||
| 497 | private TaskQueue queue; | ||
| 498 | |||
| 499 | TimerThread(TaskQueue queue) { | ||
| 500 | this.queue = queue; | ||
| 501 | } | ||
| 502 | |||
| 503 | public void run() { | ||
| 504 | try { | ||
| 505 | mainLoop(); | ||
| 506 | } finally { | ||
| 507 | // Someone killed this Thread, behave as if Timer cancelled | ||
| 508 | synchronized(queue) { | ||
| 509 | newTasksMayBeScheduled = false; | ||
| 510 | queue.clear(); // Eliminate obsolete references | ||
| 511 | } | ||
| 512 | } | ||
| 513 | } | ||
| 514 | |||
| 515 | /** | ||
| 516 | * The main timer loop. (See class comment.) | ||
| 517 | */ | ||
| 518 | private void mainLoop() { | ||
| 519 | while (true) { | ||
| 520 | try { | ||
| 521 | TimerTask task; | ||
| 522 | boolean taskFired; | ||
| 523 | synchronized(queue) { | ||
| 524 | // Wait for queue to become non-empty | ||
| 525 | while (queue.isEmpty() && newTasksMayBeScheduled) | ||
| 526 | queue.wait(); | ||
| 527 | if (queue.isEmpty()) | ||
| 528 | break; // Queue is empty and will forever remain; die | ||
| 529 | |||
| 530 | // Queue nonempty; look at first evt and do the right thing | ||
| 531 | long currentTime, executionTime; | ||
| 532 | task = queue.getMin(); | ||
| 533 | synchronized(task.lock) { | ||
| 534 | if (task.state == TimerTask.CANCELLED) { | ||
| 535 | queue.removeMin(); | ||
| 536 | continue; // No action required, poll queue again | ||
| 537 | } | ||
| 538 | currentTime = System.currentTimeMillis(); | ||
| 539 | executionTime = task.nextExecutionTime; | ||
| 540 | if (taskFired = (executionTime<=currentTime)) { | ||
| 541 | if (task.period == 0) { // Non-repeating, remove | ||
| 542 | queue.removeMin(); | ||
| 543 | task.state = TimerTask.EXECUTED; | ||
| 544 | } else { // Repeating task, reschedule | ||
| 545 | queue.rescheduleMin( | ||
| 546 | task.period<0 ? currentTime - task.period | ||
| 547 | : executionTime + task.period); | ||
| 548 | } | ||
| 549 | } | ||
| 550 | } | ||
| 551 | if (!taskFired) // Task hasn't yet fired; wait | ||
| 552 | queue.wait(executionTime - currentTime); | ||
| 553 | } | ||
| 554 | if (taskFired) // Task fired; run it, holding no locks | ||
| 555 | task.run(); | ||
| 556 | } catch(InterruptedException e) { | ||
| 557 | } | ||
| 558 | } | ||
| 559 | } | ||
| 560 | } | ||
| 561 | |||
| 562 | /** | ||
| 563 | * This class represents a timer task queue: a priority queue of TimerTasks, | ||
| 564 | * ordered on nextExecutionTime. Each Timer object has one of these, which it | ||
| 565 | * shares with its TimerThread. Internally this class uses a heap, which | ||
| 566 | * offers log(n) performance for the add, removeMin and rescheduleMin | ||
| 567 | * operations, and constant time performance for the getMin operation. | ||
| 568 | */ | ||
| 569 | class TaskQueue { | ||
| 570 | /** | ||
| 571 | * Priority queue represented as a balanced binary heap: the two children | ||
| 572 | * of queue[n] are queue[2*n] and queue[2*n+1]. The priority queue is | ||
| 573 | * ordered on the nextExecutionTime field: The TimerTask with the lowest | ||
| 574 | * nextExecutionTime is in queue[1] (assuming the queue is nonempty). For | ||
| 575 | * each node n in the heap, and each descendant of n, d, | ||
| 576 | * n.nextExecutionTime <= d.nextExecutionTime. | ||
| 577 | */ | ||
| 578 | private TimerTask[] queue = new TimerTask[128]; | ||
| 579 | |||
| 580 | /** | ||
| 581 | * The number of tasks in the priority queue. (The tasks are stored in | ||
| 582 | * queue[1] up to queue[size]). | ||
| 583 | */ | ||
| 584 | private int size = 0; | ||
| 585 | |||
| 586 | /** | ||
| 587 | * Returns the number of tasks currently on the queue. | ||
| 588 | */ | ||
| 589 | int size() { | ||
| 590 | return size; | ||
| 591 | } | ||
| 592 | |||
| 593 | /** | ||
| 594 | * Adds a new task to the priority queue. | ||
| 595 | */ | ||
| 596 | void add(TimerTask task) { | ||
| 597 | // Grow backing store if necessary | ||
| 598 | if (size + 1 == queue.length) | ||
| 599 | queue = Arrays.copyOf(queue, 2*queue.length); | ||
| 600 | |||
| 601 | queue[++size] = task; | ||
| 602 | fixUp(size); | ||
| 603 | } | ||
| 604 | |||
| 605 | /** | ||
| 606 | * Return the "head task" of the priority queue. (The head task is an | ||
| 607 | * task with the lowest nextExecutionTime.) | ||
| 608 | */ | ||
| 609 | TimerTask getMin() { | ||
| 610 | return queue[1]; | ||
| 611 | } | ||
| 612 | |||
| 613 | /** | ||
| 614 | * Return the ith task in the priority queue, where i ranges from 1 (the | ||
| 615 | * head task, which is returned by getMin) to the number of tasks on the | ||
| 616 | * queue, inclusive. | ||
| 617 | */ | ||
| 618 | TimerTask get(int i) { | ||
| 619 | return queue[i]; | ||
| 620 | } | ||
| 621 | |||
| 622 | /** | ||
| 623 | * Remove the head task from the priority queue. | ||
| 624 | */ | ||
| 625 | void removeMin() { | ||
| 626 | queue[1] = queue[size]; | ||
| 627 | queue[size--] = null; // Drop extra reference to prevent memory leak | ||
| 628 | fixDown(1); | ||
| 629 | } | ||
| 630 | |||
| 631 | /** | ||
| 632 | * Removes the ith element from queue without regard for maintaining | ||
| 633 | * the heap invariant. Recall that queue is one-based, so | ||
| 634 | * 1 <= i <= size. | ||
| 635 | */ | ||
| 636 | void quickRemove(int i) { | ||
| 637 | assert i <= size; | ||
| 638 | |||
| 639 | queue[i] = queue[size]; | ||
| 640 | queue[size--] = null; // Drop extra ref to prevent memory leak | ||
| 641 | } | ||
| 642 | |||
| 643 | /** | ||
| 644 | * Sets the nextExecutionTime associated with the head task to the | ||
| 645 | * specified value, and adjusts priority queue accordingly. | ||
| 646 | */ | ||
| 647 | void rescheduleMin(long newTime) { | ||
| 648 | queue[1].nextExecutionTime = newTime; | ||
| 649 | fixDown(1); | ||
| 650 | } | ||
| 651 | |||
| 652 | /** | ||
| 653 | * Returns true if the priority queue contains no elements. | ||
| 654 | */ | ||
| 655 | boolean isEmpty() { | ||
| 656 | return size==0; | ||
| 657 | } | ||
| 658 | |||
| 659 | /** | ||
| 660 | * Removes all elements from the priority queue. | ||
| 661 | */ | ||
| 662 | void clear() { | ||
| 663 | // Null out task references to prevent memory leak | ||
| 664 | for (int i=1; i<=size; i++) | ||
| 665 | queue[i] = null; | ||
| 666 | |||
| 667 | size = 0; | ||
| 668 | } | ||
| 669 | |||
| 670 | /** | ||
| 671 | * Establishes the heap invariant (described above) assuming the heap | ||
| 672 | * satisfies the invariant except possibly for the leaf-node indexed by k | ||
| 673 | * (which may have a nextExecutionTime less than its parent's). | ||
| 674 | * | ||
| 675 | * This method functions by "promoting" queue[k] up the hierarchy | ||
| 676 | * (by swapping it with its parent) repeatedly until queue[k]'s | ||
| 677 | * nextExecutionTime is greater than or equal to that of its parent. | ||
| 678 | */ | ||
| 679 | private void fixUp(int k) { | ||
| 680 | while (k > 1) { | ||
| 681 | int j = k >> 1; | ||
| 682 | if (queue[j].nextExecutionTime <= queue[k].nextExecutionTime) | ||
| 683 | break; | ||
| 684 | TimerTask tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; | ||
| 685 | k = j; | ||
| 686 | } | ||
| 687 | } | ||
| 688 | |||
| 689 | /** | ||
| 690 | * Establishes the heap invariant (described above) in the subtree | ||
| 691 | * rooted at k, which is assumed to satisfy the heap invariant except | ||
| 692 | * possibly for node k itself (which may have a nextExecutionTime greater | ||
| 693 | * than its children's). | ||
| 694 | * | ||
| 695 | * This method functions by "demoting" queue[k] down the hierarchy | ||
| 696 | * (by swapping it with its smaller child) repeatedly until queue[k]'s | ||
| 697 | * nextExecutionTime is less than or equal to those of its children. | ||
| 698 | */ | ||
| 699 | private void fixDown(int k) { | ||
| 700 | int j; | ||
| 701 | while ((j = k << 1) <= size && j > 0) { | ||
| 702 | if (j < size && | ||
| 703 | queue[j].nextExecutionTime > queue[j+1].nextExecutionTime) | ||
| 704 | j++; // j indexes smallest kid | ||
| 705 | if (queue[k].nextExecutionTime <= queue[j].nextExecutionTime) | ||
| 706 | break; | ||
| 707 | TimerTask tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; | ||
| 708 | k = j; | ||
| 709 | } | ||
| 710 | } | ||
| 711 | |||
| 712 | /** | ||
| 713 | * Establishes the heap invariant (described above) in the entire tree, | ||
| 714 | * assuming nothing about the order of the elements prior to the call. | ||
| 715 | */ | ||
| 716 | void heapify() { | ||
| 717 | for (int i = size/2; i >= 1; i--) | ||
| 718 | fixDown(i); | ||
| 719 | } | ||
| 720 | } | ||