/* * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util;import java.util.Date;import java.util.concurrent.atomic.AtomicInteger; /** * A facility for threads to schedule tasks for future execution in a * background thread. Tasks may be scheduled for one-time execution, or for * repeated execution at regular intervals. * * <p>Corresponding to each <tt>Timer</tt> object is a single background * thread that is used to execute all of the timer's tasks, sequentially. * Timer tasks should complete quickly. If a timer task takes excessive time * to complete, it "hogs" the timer's task execution thread. This can, in * turn, delay the execution of subsequent tasks, which may "bunch up" and * execute in rapid succession when (and if) the offending task finally * completes. * * <p>After the last live reference to a <tt>Timer</tt> object goes away * <i>and</i> all outstanding tasks have completed execution, the timer's task * execution thread terminates gracefully (and becomes subject to garbage * collection). However, this can take arbitrarily long to occur. By * default, the task execution thread does not run as a <i>daemon thread</i>, * so it is capable of keeping an application from terminating. If a caller * wants to terminate a timer's task execution thread rapidly, the caller * should invoke the timer's <tt>cancel</tt> method. * * <p>If the timer's task execution thread terminates unexpectedly, for * example, because its <tt>stop</tt> method is invoked, any further * attempt to schedule a task on the timer will result in an * <tt>IllegalStateException</tt>, as if the timer's <tt>cancel</tt> * method had been invoked. * * <p>This class is thread-safe: multiple threads can share a single * <tt>Timer</tt> object without the need for external synchronization. * * <p>This class does <i>not</i> offer real-time guarantees: it schedules * tasks using the <tt>Object.wait(long)</tt> method. * * <p>Java 5.0 introduced the {@code java.util.concurrent} package and * one of the concurrency utilities therein is the {@link * java.util.concurrent.ScheduledThreadPoolExecutor * ScheduledThreadPoolExecutor} which is a thread pool for repeatedly * executing tasks at a given rate or delay. It is effectively a more * versatile replacement for the {@code Timer}/{@code TimerTask} * combination, as it allows multiple service threads, accepts various * time units, and doesn't require subclassing {@code TimerTask} (just * implement {@code Runnable}). Configuring {@code * ScheduledThreadPoolExecutor} with one thread makes it equivalent to * {@code Timer}. * * <p>Implementation note: This class scales to large numbers of concurrently * scheduled tasks (thousands should present no problem). Internally, * it uses a binary heap to represent its task queue, so the cost to schedule * a task is O(log n), where n is the number of concurrently scheduled tasks. * * <p>Implementation note: All constructors start a timer thread. * * @author Josh Bloch * @see TimerTask * @see Object#wait(long) * @since 1.3 */ public class Timer { /** * The timer task queue. This data structure is shared with the timer * thread. The timer produces tasks, via its various schedule calls, * and the timer thread consumes, executing timer tasks as appropriate, * and removing them from the queue when they're obsolete. */ private final TaskQueue queue = new TaskQueue(); /** * The timer thread. */ private final TimerThread thread = new TimerThread(queue); /** * This object causes the timer's task execution thread to exit * gracefully when there are no live references to the Timer object and no * tasks in the timer queue. It is used in preference to a finalizer on * Timer as such a finalizer would be susceptible to a subclass's * finalizer forgetting to call it. */ private final Object threadReaper = new Object() { protected void finalize() throws Throwable { synchronized(queue) { thread.newTasksMayBeScheduled = false; queue.notify(); // In case queue is empty. } } }; /** * This ID is used to generate thread names. */ private final static AtomicInteger nextSerialNumber = new AtomicInteger(0); private static int serialNumber() { return nextSerialNumber.getAndIncrement(); } /** * Creates a new timer. The associated thread does <i>not</i> * {@linkplain Thread#setDaemon run as a daemon}. */ public Timer() { this("Timer-" + serialNumber()); } /** * Creates a new timer whose associated thread may be specified to * {@linkplain Thread#setDaemon run as a daemon}. * A daemon thread is called for if the timer will be used to * schedule repeating "maintenance activities", which must be * performed as long as the application is running, but should not * prolong the lifetime of the application. * * @param isDaemon true if the associated thread should run as a daemon. */ public Timer(boolean isDaemon) { this("Timer-" + serialNumber(), isDaemon); } /** * Creates a new timer whose associated thread has the specified name. * The associated thread does <i>not</i> * {@linkplain Thread#setDaemon run as a daemon}. * * @param name the name of the associated thread * @throws NullPointerException if {@code name} is null * @since 1.5 */ public Timer(String name) { thread.setName(name); thread.start(); } /** * Creates a new timer whose associated thread has the specified name, * and may be specified to * {@linkplain Thread#setDaemon run as a daemon}. * * @param name the name of the associated thread * @param isDaemon true if the associated thread should run as a daemon * @throws NullPointerException if {@code name} is null * @since 1.5 */ public Timer(String name, boolean isDaemon) { thread.setName(name); thread.setDaemon(isDaemon); thread.start(); } /** * Schedules the specified task for execution after the specified delay. * * @param task task to be scheduled. * @param delay delay in milliseconds before task is to be executed. * @throws IllegalArgumentException if <tt>delay</tt> is negative, or * <tt>delay + System.currentTimeMillis()</tt> is negative. * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ public void schedule(TimerTask task, long delay) { if (delay < 0) throw new IllegalArgumentException("Negative delay."); sched(task, System.currentTimeMillis()+delay, 0); } /** * Schedules the specified task for execution at the specified time. If * the time is in the past, the task is scheduled for immediate execution. * * @param task task to be scheduled. * @param time time at which task is to be executed. * @throws IllegalArgumentException if <tt>time.getTime()</tt> is negative. * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} or {@code time} is null */ public void schedule(TimerTask task, Date time) { sched(task, time.getTime(), 0); } /** * Schedules the specified task for repeated <i>fixed-delay execution</i>, * beginning after the specified delay. Subsequent executions take place * at approximately regular intervals separated by the specified period. * * <p>In fixed-delay execution, each execution is scheduled relative to * the actual execution time of the previous execution. If an execution * is delayed for any reason (such as garbage collection or other * background activity), subsequent executions will be delayed as well. * In the long run, the frequency of execution will generally be slightly * lower than the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). * * <p>Fixed-delay execution is appropriate for recurring activities * that require "smoothness." In other words, it is appropriate for * activities where it is more important to keep the frequency accurate * in the short run than in the long run. This includes most animation * tasks, such as blinking a cursor at regular intervals. It also includes * tasks wherein regular activity is performed in response to human * input, such as automatically repeating a character as long as a key * is held down. * * @param task task to be scheduled. * @param delay delay in milliseconds before task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code delay < 0}, or * {@code delay + System.currentTimeMillis() < 0}, or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ public void schedule(TimerTask task, long delay, long period) { if (delay < 0) throw new IllegalArgumentException("Negative delay."); if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, System.currentTimeMillis()+delay, -period); } /** * Schedules the specified task for repeated <i>fixed-delay execution</i>, * beginning at the specified time. Subsequent executions take place at * approximately regular intervals, separated by the specified period. * * <p>In fixed-delay execution, each execution is scheduled relative to * the actual execution time of the previous execution. If an execution * is delayed for any reason (such as garbage collection or other * background activity), subsequent executions will be delayed as well. * In the long run, the frequency of execution will generally be slightly * lower than the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). As a * consequence of the above, if the scheduled first time is in the past, * it is scheduled for immediate execution. * * <p>Fixed-delay execution is appropriate for recurring activities * that require "smoothness." In other words, it is appropriate for * activities where it is more important to keep the frequency accurate * in the short run than in the long run. This includes most animation * tasks, such as blinking a cursor at regular intervals. It also includes * tasks wherein regular activity is performed in response to human * input, such as automatically repeating a character as long as a key * is held down. * * @param task task to be scheduled. * @param firstTime First time at which task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code firstTime.getTime() < 0}, or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} or {@code firstTime} is null */ public void schedule(TimerTask task, Date firstTime, long period) { if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, firstTime.getTime(), -period); } /** * Schedules the specified task for repeated <i>fixed-rate execution</i>, * beginning after the specified delay. Subsequent executions take place * at approximately regular intervals, separated by the specified period. * * <p>In fixed-rate execution, each execution is scheduled relative to the * scheduled execution time of the initial execution. If an execution is * delayed for any reason (such as garbage collection or other background * activity), two or more executions will occur in rapid succession to * "catch up." In the long run, the frequency of execution will be * exactly the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). * * <p>Fixed-rate execution is appropriate for recurring activities that * are sensitive to <i>absolute</i> time, such as ringing a chime every * hour on the hour, or running scheduled maintenance every day at a * particular time. It is also appropriate for recurring activities * where the total time to perform a fixed number of executions is * important, such as a countdown timer that ticks once every second for * ten seconds. Finally, fixed-rate execution is appropriate for * scheduling multiple repeating timer tasks that must remain synchronized * with respect to one another. * * @param task task to be scheduled. * @param delay delay in milliseconds before task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code delay < 0}, or * {@code delay + System.currentTimeMillis() < 0}, or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ public void scheduleAtFixedRate(TimerTask task, long delay, long period) { if (delay < 0) throw new IllegalArgumentException("Negative delay."); if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, System.currentTimeMillis()+delay, period); } /** * Schedules the specified task for repeated <i>fixed-rate execution</i>, * beginning at the specified time. Subsequent executions take place at * approximately regular intervals, separated by the specified period. * * <p>In fixed-rate execution, each execution is scheduled relative to the * scheduled execution time of the initial execution. If an execution is * delayed for any reason (such as garbage collection or other background * activity), two or more executions will occur in rapid succession to * "catch up." In the long run, the frequency of execution will be * exactly the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). As a * consequence of the above, if the scheduled first time is in the past, * then any "missed" executions will be scheduled for immediate "catch up" * execution. * * <p>Fixed-rate execution is appropriate for recurring activities that * are sensitive to <i>absolute</i> time, such as ringing a chime every * hour on the hour, or running scheduled maintenance every day at a * particular time. It is also appropriate for recurring activities * where the total time to perform a fixed number of executions is * important, such as a countdown timer that ticks once every second for * ten seconds. Finally, fixed-rate execution is appropriate for * scheduling multiple repeating timer tasks that must remain synchronized * with respect to one another. * * @param task task to be scheduled. * @param firstTime First time at which task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code firstTime.getTime() < 0} or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} or {@code firstTime} is null */ public void scheduleAtFixedRate(TimerTask task, Date firstTime, long period) { if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, firstTime.getTime(), period); } /** * Schedule the specified timer task for execution at the specified * time with the specified period, in milliseconds. If period is * positive, the task is scheduled for repeated execution; if period is * zero, the task is scheduled for one-time execution. Time is specified * in Date.getTime() format. This method checks timer state, task state, * and initial execution time, but not period. * * @throws IllegalArgumentException if <tt>time</tt> is negative. * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ private void sched(TimerTask task, long time, long period) { if (time < 0) throw new IllegalArgumentException("Illegal execution time."); // Constrain value of period sufficiently to prevent numeric // overflow while still being effectively infinitely large. if (Math.abs(period) > (Long.MAX_VALUE >> 1)) period >>= 1; synchronized(queue) { if (!thread.newTasksMayBeScheduled) throw new IllegalStateException("Timer already cancelled."); synchronized(task.lock) { if (task.state != TimerTask.VIRGIN) throw new IllegalStateException( "Task already scheduled or cancelled"); task.nextExecutionTime = time; task.period = period; task.state = TimerTask.SCHEDULED; } queue.add(task); if (queue.getMin() == task) queue.notify(); } } /** * Terminates this timer, discarding any currently scheduled tasks. * Does not interfere with a currently executing task (if it exists). * Once a timer has been terminated, its execution thread terminates * gracefully, and no more tasks may be scheduled on it. * * <p>Note that calling this method from within the run method of a * timer task that was invoked by this timer absolutely guarantees that * the ongoing task execution is the last task execution that will ever * be performed by this timer. * * <p>This method may be called repeatedly; the second and subsequent * calls have no effect. */ public void cancel() { synchronized(queue) { thread.newTasksMayBeScheduled = false; queue.clear(); queue.notify(); // In case queue was already empty. } } /** * Removes all cancelled tasks from this timer's task queue. <i>Calling * this method has no effect on the behavior of the timer</i>, but * eliminates the references to the cancelled tasks from the queue. * If there are no external references to these tasks, they become * eligible for garbage collection. * * <p>Most programs will have no need to call this method. * It is designed for use by the rare application that cancels a large * number of tasks. Calling this method trades time for space: the * runtime of the method may be proportional to n + c log n, where n * is the number of tasks in the queue and c is the number of cancelled * tasks. * * <p>Note that it is permissible to call this method from within a * a task scheduled on this timer. * * @return the number of tasks removed from the queue. * @since 1.5 */ public int purge() { int result = 0; synchronized(queue) { for (int i = queue.size(); i > 0; i--) { if (queue.get(i).state == TimerTask.CANCELLED) { queue.quickRemove(i); result++; } } if (result != 0) queue.heapify(); } return result; }} /** * This "helper class" implements the timer's task execution thread, which * waits for tasks on the timer queue, executions them when they fire, * reschedules repeating tasks, and removes cancelled tasks and spent * non-repeating tasks from the queue. */class TimerThread extends Thread { /** * This flag is set to false by the reaper to inform us that there * are no more live references to our Timer object. Once this flag * is true and there are no more tasks in our queue, there is no * work left for us to do, so we terminate gracefully. Note that * this field is protected by queue's monitor! */ boolean newTasksMayBeScheduled = true; /** * Our Timer's queue. We store this reference in preference to * a reference to the Timer so the reference graph remains acyclic. * Otherwise, the Timer would never be garbage-collected and this * thread would never go away. */ private TaskQueue queue; TimerThread(TaskQueue queue) { this.queue = queue;Lines 1–500 of 720. Load more
/* * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; import java.util.Date; import java.util.concurrent.atomic.AtomicInteger; /** * A facility for threads to schedule tasks for future execution in a * background thread. Tasks may be scheduled for one-time execution, or for * repeated execution at regular intervals. * * <p>Corresponding to each <tt>Timer</tt> object is a single background * thread that is used to execute all of the timer's tasks, sequentially. * Timer tasks should complete quickly. If a timer task takes excessive time * to complete, it "hogs" the timer's task execution thread. This can, in * turn, delay the execution of subsequent tasks, which may "bunch up" and * execute in rapid succession when (and if) the offending task finally * completes. * * <p>After the last live reference to a <tt>Timer</tt> object goes away * <i>and</i> all outstanding tasks have completed execution, the timer's task * execution thread terminates gracefully (and becomes subject to garbage * collection). However, this can take arbitrarily long to occur. By * default, the task execution thread does not run as a <i>daemon thread</i>, * so it is capable of keeping an application from terminating. If a caller * wants to terminate a timer's task execution thread rapidly, the caller * should invoke the timer's <tt>cancel</tt> method. * * <p>If the timer's task execution thread terminates unexpectedly, for * example, because its <tt>stop</tt> method is invoked, any further * attempt to schedule a task on the timer will result in an * <tt>IllegalStateException</tt>, as if the timer's <tt>cancel</tt> * method had been invoked. * * <p>This class is thread-safe: multiple threads can share a single * <tt>Timer</tt> object without the need for external synchronization. * * <p>This class does <i>not</i> offer real-time guarantees: it schedules * tasks using the <tt>Object.wait(long)</tt> method. * * <p>Java 5.0 introduced the {@code java.util.concurrent} package and * one of the concurrency utilities therein is the {@link * java.util.concurrent.ScheduledThreadPoolExecutor * ScheduledThreadPoolExecutor} which is a thread pool for repeatedly * executing tasks at a given rate or delay. It is effectively a more * versatile replacement for the {@code Timer}/{@code TimerTask} * combination, as it allows multiple service threads, accepts various * time units, and doesn't require subclassing {@code TimerTask} (just * implement {@code Runnable}). Configuring {@code * ScheduledThreadPoolExecutor} with one thread makes it equivalent to * {@code Timer}. * * <p>Implementation note: This class scales to large numbers of concurrently * scheduled tasks (thousands should present no problem). Internally, * it uses a binary heap to represent its task queue, so the cost to schedule * a task is O(log n), where n is the number of concurrently scheduled tasks. * * <p>Implementation note: All constructors start a timer thread. * * @author Josh Bloch * @see TimerTask * @see Object#wait(long) * @since 1.3 */ public class Timer { /** * The timer task queue. This data structure is shared with the timer * thread. The timer produces tasks, via its various schedule calls, * and the timer thread consumes, executing timer tasks as appropriate, * and removing them from the queue when they're obsolete. */ private final TaskQueue queue = new TaskQueue(); /** * The timer thread. */ private final TimerThread thread = new TimerThread(queue); /** * This object causes the timer's task execution thread to exit * gracefully when there are no live references to the Timer object and no * tasks in the timer queue. It is used in preference to a finalizer on * Timer as such a finalizer would be susceptible to a subclass's * finalizer forgetting to call it. */ private final Object threadReaper = new Object() { protected void finalize() throws Throwable { synchronized(queue) { thread.newTasksMayBeScheduled = false; queue.notify(); // In case queue is empty. } } }; /** * This ID is used to generate thread names. */ private final static AtomicInteger nextSerialNumber = new AtomicInteger(0); private static int serialNumber() { return nextSerialNumber.getAndIncrement(); } /** * Creates a new timer. The associated thread does <i>not</i> * {@linkplain Thread#setDaemon run as a daemon}. */ public Timer() { this("Timer-" + serialNumber()); } /** * Creates a new timer whose associated thread may be specified to * {@linkplain Thread#setDaemon run as a daemon}. * A daemon thread is called for if the timer will be used to * schedule repeating "maintenance activities", which must be * performed as long as the application is running, but should not * prolong the lifetime of the application. * * @param isDaemon true if the associated thread should run as a daemon. */ public Timer(boolean isDaemon) { this("Timer-" + serialNumber(), isDaemon); } /** * Creates a new timer whose associated thread has the specified name. * The associated thread does <i>not</i> * {@linkplain Thread#setDaemon run as a daemon}. * * @param name the name of the associated thread * @throws NullPointerException if {@code name} is null * @since 1.5 */ public Timer(String name) { thread.setName(name); thread.start(); } /** * Creates a new timer whose associated thread has the specified name, * and may be specified to * {@linkplain Thread#setDaemon run as a daemon}. * * @param name the name of the associated thread * @param isDaemon true if the associated thread should run as a daemon * @throws NullPointerException if {@code name} is null * @since 1.5 */ public Timer(String name, boolean isDaemon) { thread.setName(name); thread.setDaemon(isDaemon); thread.start(); } /** * Schedules the specified task for execution after the specified delay. * * @param task task to be scheduled. * @param delay delay in milliseconds before task is to be executed. * @throws IllegalArgumentException if <tt>delay</tt> is negative, or * <tt>delay + System.currentTimeMillis()</tt> is negative. * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ public void schedule(TimerTask task, long delay) { if (delay < 0) throw new IllegalArgumentException("Negative delay."); sched(task, System.currentTimeMillis()+delay, 0); } /** * Schedules the specified task for execution at the specified time. If * the time is in the past, the task is scheduled for immediate execution. * * @param task task to be scheduled. * @param time time at which task is to be executed. * @throws IllegalArgumentException if <tt>time.getTime()</tt> is negative. * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} or {@code time} is null */ public void schedule(TimerTask task, Date time) { sched(task, time.getTime(), 0); } /** * Schedules the specified task for repeated <i>fixed-delay execution</i>, * beginning after the specified delay. Subsequent executions take place * at approximately regular intervals separated by the specified period. * * <p>In fixed-delay execution, each execution is scheduled relative to * the actual execution time of the previous execution. If an execution * is delayed for any reason (such as garbage collection or other * background activity), subsequent executions will be delayed as well. * In the long run, the frequency of execution will generally be slightly * lower than the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). * * <p>Fixed-delay execution is appropriate for recurring activities * that require "smoothness." In other words, it is appropriate for * activities where it is more important to keep the frequency accurate * in the short run than in the long run. This includes most animation * tasks, such as blinking a cursor at regular intervals. It also includes * tasks wherein regular activity is performed in response to human * input, such as automatically repeating a character as long as a key * is held down. * * @param task task to be scheduled. * @param delay delay in milliseconds before task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code delay < 0}, or * {@code delay + System.currentTimeMillis() < 0}, or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ public void schedule(TimerTask task, long delay, long period) { if (delay < 0) throw new IllegalArgumentException("Negative delay."); if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, System.currentTimeMillis()+delay, -period); } /** * Schedules the specified task for repeated <i>fixed-delay execution</i>, * beginning at the specified time. Subsequent executions take place at * approximately regular intervals, separated by the specified period. * * <p>In fixed-delay execution, each execution is scheduled relative to * the actual execution time of the previous execution. If an execution * is delayed for any reason (such as garbage collection or other * background activity), subsequent executions will be delayed as well. * In the long run, the frequency of execution will generally be slightly * lower than the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). As a * consequence of the above, if the scheduled first time is in the past, * it is scheduled for immediate execution. * * <p>Fixed-delay execution is appropriate for recurring activities * that require "smoothness." In other words, it is appropriate for * activities where it is more important to keep the frequency accurate * in the short run than in the long run. This includes most animation * tasks, such as blinking a cursor at regular intervals. It also includes * tasks wherein regular activity is performed in response to human * input, such as automatically repeating a character as long as a key * is held down. * * @param task task to be scheduled. * @param firstTime First time at which task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code firstTime.getTime() < 0}, or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} or {@code firstTime} is null */ public void schedule(TimerTask task, Date firstTime, long period) { if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, firstTime.getTime(), -period); } /** * Schedules the specified task for repeated <i>fixed-rate execution</i>, * beginning after the specified delay. Subsequent executions take place * at approximately regular intervals, separated by the specified period. * * <p>In fixed-rate execution, each execution is scheduled relative to the * scheduled execution time of the initial execution. If an execution is * delayed for any reason (such as garbage collection or other background * activity), two or more executions will occur in rapid succession to * "catch up." In the long run, the frequency of execution will be * exactly the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). * * <p>Fixed-rate execution is appropriate for recurring activities that * are sensitive to <i>absolute</i> time, such as ringing a chime every * hour on the hour, or running scheduled maintenance every day at a * particular time. It is also appropriate for recurring activities * where the total time to perform a fixed number of executions is * important, such as a countdown timer that ticks once every second for * ten seconds. Finally, fixed-rate execution is appropriate for * scheduling multiple repeating timer tasks that must remain synchronized * with respect to one another. * * @param task task to be scheduled. * @param delay delay in milliseconds before task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code delay < 0}, or * {@code delay + System.currentTimeMillis() < 0}, or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ public void scheduleAtFixedRate(TimerTask task, long delay, long period) { if (delay < 0) throw new IllegalArgumentException("Negative delay."); if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, System.currentTimeMillis()+delay, period); } /** * Schedules the specified task for repeated <i>fixed-rate execution</i>, * beginning at the specified time. Subsequent executions take place at * approximately regular intervals, separated by the specified period. * * <p>In fixed-rate execution, each execution is scheduled relative to the * scheduled execution time of the initial execution. If an execution is * delayed for any reason (such as garbage collection or other background * activity), two or more executions will occur in rapid succession to * "catch up." In the long run, the frequency of execution will be * exactly the reciprocal of the specified period (assuming the system * clock underlying <tt>Object.wait(long)</tt> is accurate). As a * consequence of the above, if the scheduled first time is in the past, * then any "missed" executions will be scheduled for immediate "catch up" * execution. * * <p>Fixed-rate execution is appropriate for recurring activities that * are sensitive to <i>absolute</i> time, such as ringing a chime every * hour on the hour, or running scheduled maintenance every day at a * particular time. It is also appropriate for recurring activities * where the total time to perform a fixed number of executions is * important, such as a countdown timer that ticks once every second for * ten seconds. Finally, fixed-rate execution is appropriate for * scheduling multiple repeating timer tasks that must remain synchronized * with respect to one another. * * @param task task to be scheduled. * @param firstTime First time at which task is to be executed. * @param period time in milliseconds between successive task executions. * @throws IllegalArgumentException if {@code firstTime.getTime() < 0} or * {@code period <= 0} * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} or {@code firstTime} is null */ public void scheduleAtFixedRate(TimerTask task, Date firstTime, long period) { if (period <= 0) throw new IllegalArgumentException("Non-positive period."); sched(task, firstTime.getTime(), period); } /** * Schedule the specified timer task for execution at the specified * time with the specified period, in milliseconds. If period is * positive, the task is scheduled for repeated execution; if period is * zero, the task is scheduled for one-time execution. Time is specified * in Date.getTime() format. This method checks timer state, task state, * and initial execution time, but not period. * * @throws IllegalArgumentException if <tt>time</tt> is negative. * @throws IllegalStateException if task was already scheduled or * cancelled, timer was cancelled, or timer thread terminated. * @throws NullPointerException if {@code task} is null */ private void sched(TimerTask task, long time, long period) { if (time < 0) throw new IllegalArgumentException("Illegal execution time."); // Constrain value of period sufficiently to prevent numeric // overflow while still being effectively infinitely large. if (Math.abs(period) > (Long.MAX_VALUE >> 1)) period >>= 1; synchronized(queue) { if (!thread.newTasksMayBeScheduled) throw new IllegalStateException("Timer already cancelled."); synchronized(task.lock) { if (task.state != TimerTask.VIRGIN) throw new IllegalStateException( "Task already scheduled or cancelled"); task.nextExecutionTime = time; task.period = period; task.state = TimerTask.SCHEDULED; } queue.add(task); if (queue.getMin() == task) queue.notify(); } } /** * Terminates this timer, discarding any currently scheduled tasks. * Does not interfere with a currently executing task (if it exists). * Once a timer has been terminated, its execution thread terminates * gracefully, and no more tasks may be scheduled on it. * * <p>Note that calling this method from within the run method of a * timer task that was invoked by this timer absolutely guarantees that * the ongoing task execution is the last task execution that will ever * be performed by this timer. * * <p>This method may be called repeatedly; the second and subsequent * calls have no effect. */ public void cancel() { synchronized(queue) { thread.newTasksMayBeScheduled = false; queue.clear(); queue.notify(); // In case queue was already empty. } } /** * Removes all cancelled tasks from this timer's task queue. <i>Calling * this method has no effect on the behavior of the timer</i>, but * eliminates the references to the cancelled tasks from the queue. * If there are no external references to these tasks, they become * eligible for garbage collection. * * <p>Most programs will have no need to call this method. * It is designed for use by the rare application that cancels a large * number of tasks. Calling this method trades time for space: the * runtime of the method may be proportional to n + c log n, where n * is the number of tasks in the queue and c is the number of cancelled * tasks. * * <p>Note that it is permissible to call this method from within a * a task scheduled on this timer. * * @return the number of tasks removed from the queue. * @since 1.5 */ public int purge() { int result = 0; synchronized(queue) { for (int i = queue.size(); i > 0; i--) { if (queue.get(i).state == TimerTask.CANCELLED) { queue.quickRemove(i); result++; } } if (result != 0) queue.heapify(); } return result; } } /** * This "helper class" implements the timer's task execution thread, which * waits for tasks on the timer queue, executions them when they fire, * reschedules repeating tasks, and removes cancelled tasks and spent * non-repeating tasks from the queue. */ class TimerThread extends Thread { /** * This flag is set to false by the reaper to inform us that there * are no more live references to our Timer object. Once this flag * is true and there are no more tasks in our queue, there is no * work left for us to do, so we terminate gracefully. Note that * this field is protected by queue's monitor! */ boolean newTasksMayBeScheduled = true; /** * Our Timer's queue. We store this reference in preference to * a reference to the Timer so the reference graph remains acyclic. * Otherwise, the Timer would never be garbage-collected and this * thread would never go away. */ private TaskQueue queue; TimerThread(TaskQueue queue) { this.queue = queue;