# HG changeset patch # User Jaroslav Tulach # Date 1383407028 -3600 # Node ID 161772460817d364604ddf7a526ee82ed0f37f42 # Parent 60ca4f72a70cc4e952a50cee7aa2cadc4ff359c1# Parent f8f4cf9046fd1d657456cf04e158b73aba51700a Merging in timer diff -r 60ca4f72a70c -r 161772460817 rt/emul/compact/src/main/java/java/util/Timer.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/rt/emul/compact/src/main/java/java/util/Timer.java Sat Nov 02 16:43:48 2013 +0100 @@ -0,0 +1,720 @@ +/* + * 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. + * + *

Corresponding to each Timer 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. + * + *

After the last live reference to a Timer object goes away + * and 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 daemon thread, + * 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 cancel method. + * + *

If the timer's task execution thread terminates unexpectedly, for + * example, because its stop method is invoked, any further + * attempt to schedule a task on the timer will result in an + * IllegalStateException, as if the timer's cancel + * method had been invoked. + * + *

This class is thread-safe: multiple threads can share a single + * Timer object without the need for external synchronization. + * + *

This class does not offer real-time guarantees: it schedules + * tasks using the Object.wait(long) method. + * + *

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}. + * + *

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. + * + *

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 not + * {@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 not + * {@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 delay is negative, or + * delay + System.currentTimeMillis() 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 time.getTime() 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 fixed-delay execution, + * beginning after the specified delay. Subsequent executions take place + * at approximately regular intervals separated by the specified period. + * + *

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 Object.wait(long) is accurate). + * + *

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 fixed-delay execution, + * beginning at the specified time. Subsequent executions take place at + * approximately regular intervals, separated by the specified period. + * + *

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 fixed-rate execution, + * beginning after the specified delay. Subsequent executions take place + * at approximately regular intervals, separated by the specified period. + * + *

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 Object.wait(long) is accurate). + * + *

Fixed-rate execution is appropriate for recurring activities that + * are sensitive to absolute 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 time 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. + * + *

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. + * + *

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. Calling + * this method has no effect on the behavior of the timer, 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. + * + *

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. + * + *

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; + } + + public void run() { + try { + mainLoop(); + } finally { + // Someone killed this Thread, behave as if Timer cancelled + synchronized(queue) { + newTasksMayBeScheduled = false; + queue.clear(); // Eliminate obsolete references + } + } + } + + /** + * The main timer loop. (See class comment.) + */ + private void mainLoop() { + while (true) { + try { + TimerTask task; + boolean taskFired; + synchronized(queue) { + // Wait for queue to become non-empty + while (queue.isEmpty() && newTasksMayBeScheduled) + queue.wait(); + if (queue.isEmpty()) + break; // Queue is empty and will forever remain; die + + // Queue nonempty; look at first evt and do the right thing + long currentTime, executionTime; + task = queue.getMin(); + synchronized(task.lock) { + if (task.state == TimerTask.CANCELLED) { + queue.removeMin(); + continue; // No action required, poll queue again + } + currentTime = System.currentTimeMillis(); + executionTime = task.nextExecutionTime; + if (taskFired = (executionTime<=currentTime)) { + if (task.period == 0) { // Non-repeating, remove + queue.removeMin(); + task.state = TimerTask.EXECUTED; + } else { // Repeating task, reschedule + queue.rescheduleMin( + task.period<0 ? currentTime - task.period + : executionTime + task.period); + } + } + } + if (!taskFired) // Task hasn't yet fired; wait + queue.wait(executionTime - currentTime); + } + if (taskFired) // Task fired; run it, holding no locks + task.run(); + } catch(InterruptedException e) { + } + } + } +} + +/** + * This class represents a timer task queue: a priority queue of TimerTasks, + * ordered on nextExecutionTime. Each Timer object has one of these, which it + * shares with its TimerThread. Internally this class uses a heap, which + * offers log(n) performance for the add, removeMin and rescheduleMin + * operations, and constant time performance for the getMin operation. + */ +class TaskQueue { + /** + * Priority queue represented as a balanced binary heap: the two children + * of queue[n] are queue[2*n] and queue[2*n+1]. The priority queue is + * ordered on the nextExecutionTime field: The TimerTask with the lowest + * nextExecutionTime is in queue[1] (assuming the queue is nonempty). For + * each node n in the heap, and each descendant of n, d, + * n.nextExecutionTime <= d.nextExecutionTime. + */ + private TimerTask[] queue = new TimerTask[128]; + + /** + * The number of tasks in the priority queue. (The tasks are stored in + * queue[1] up to queue[size]). + */ + private int size = 0; + + /** + * Returns the number of tasks currently on the queue. + */ + int size() { + return size; + } + + /** + * Adds a new task to the priority queue. + */ + void add(TimerTask task) { + // Grow backing store if necessary + if (size + 1 == queue.length) + queue = Arrays.copyOf(queue, 2*queue.length); + + queue[++size] = task; + fixUp(size); + } + + /** + * Return the "head task" of the priority queue. (The head task is an + * task with the lowest nextExecutionTime.) + */ + TimerTask getMin() { + return queue[1]; + } + + /** + * Return the ith task in the priority queue, where i ranges from 1 (the + * head task, which is returned by getMin) to the number of tasks on the + * queue, inclusive. + */ + TimerTask get(int i) { + return queue[i]; + } + + /** + * Remove the head task from the priority queue. + */ + void removeMin() { + queue[1] = queue[size]; + queue[size--] = null; // Drop extra reference to prevent memory leak + fixDown(1); + } + + /** + * Removes the ith element from queue without regard for maintaining + * the heap invariant. Recall that queue is one-based, so + * 1 <= i <= size. + */ + void quickRemove(int i) { + assert i <= size; + + queue[i] = queue[size]; + queue[size--] = null; // Drop extra ref to prevent memory leak + } + + /** + * Sets the nextExecutionTime associated with the head task to the + * specified value, and adjusts priority queue accordingly. + */ + void rescheduleMin(long newTime) { + queue[1].nextExecutionTime = newTime; + fixDown(1); + } + + /** + * Returns true if the priority queue contains no elements. + */ + boolean isEmpty() { + return size==0; + } + + /** + * Removes all elements from the priority queue. + */ + void clear() { + // Null out task references to prevent memory leak + for (int i=1; i<=size; i++) + queue[i] = null; + + size = 0; + } + + /** + * Establishes the heap invariant (described above) assuming the heap + * satisfies the invariant except possibly for the leaf-node indexed by k + * (which may have a nextExecutionTime less than its parent's). + * + * This method functions by "promoting" queue[k] up the hierarchy + * (by swapping it with its parent) repeatedly until queue[k]'s + * nextExecutionTime is greater than or equal to that of its parent. + */ + private void fixUp(int k) { + while (k > 1) { + int j = k >> 1; + if (queue[j].nextExecutionTime <= queue[k].nextExecutionTime) + break; + TimerTask tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } + + /** + * Establishes the heap invariant (described above) in the subtree + * rooted at k, which is assumed to satisfy the heap invariant except + * possibly for node k itself (which may have a nextExecutionTime greater + * than its children's). + * + * This method functions by "demoting" queue[k] down the hierarchy + * (by swapping it with its smaller child) repeatedly until queue[k]'s + * nextExecutionTime is less than or equal to those of its children. + */ + private void fixDown(int k) { + int j; + while ((j = k << 1) <= size && j > 0) { + if (j < size && + queue[j].nextExecutionTime > queue[j+1].nextExecutionTime) + j++; // j indexes smallest kid + if (queue[k].nextExecutionTime <= queue[j].nextExecutionTime) + break; + TimerTask tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } + + /** + * Establishes the heap invariant (described above) in the entire tree, + * assuming nothing about the order of the elements prior to the call. + */ + void heapify() { + for (int i = size/2; i >= 1; i--) + fixDown(i); + } +} diff -r 60ca4f72a70c -r 161772460817 rt/emul/compact/src/main/java/java/util/TimerTask.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/rt/emul/compact/src/main/java/java/util/TimerTask.java Sat Nov 02 16:43:48 2013 +0100 @@ -0,0 +1,158 @@ +/* + * Copyright (c) 1999, 2004, 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; + +/** + * A task that can be scheduled for one-time or repeated execution by a Timer. + * + * @author Josh Bloch + * @see Timer + * @since 1.3 + */ + +public abstract class TimerTask implements Runnable { + /** + * This object is used to control access to the TimerTask internals. + */ + final Object lock = new Object(); + + /** + * The state of this task, chosen from the constants below. + */ + int state = VIRGIN; + + /** + * This task has not yet been scheduled. + */ + static final int VIRGIN = 0; + + /** + * This task is scheduled for execution. If it is a non-repeating task, + * it has not yet been executed. + */ + static final int SCHEDULED = 1; + + /** + * This non-repeating task has already executed (or is currently + * executing) and has not been cancelled. + */ + static final int EXECUTED = 2; + + /** + * This task has been cancelled (with a call to TimerTask.cancel). + */ + static final int CANCELLED = 3; + + /** + * Next execution time for this task in the format returned by + * System.currentTimeMillis, assuming this task is scheduled for execution. + * For repeating tasks, this field is updated prior to each task execution. + */ + long nextExecutionTime; + + /** + * Period in milliseconds for repeating tasks. A positive value indicates + * fixed-rate execution. A negative value indicates fixed-delay execution. + * A value of 0 indicates a non-repeating task. + */ + long period = 0; + + /** + * Creates a new timer task. + */ + protected TimerTask() { + } + + /** + * The action to be performed by this timer task. + */ + public abstract void run(); + + /** + * Cancels this timer task. If the task has been scheduled for one-time + * execution and has not yet run, or has not yet been scheduled, it will + * never run. If the task has been scheduled for repeated execution, it + * will never run again. (If the task is running when this call occurs, + * the task will run to completion, but will never run again.) + * + *

Note that calling this method from within the run method of + * a repeating timer task absolutely guarantees that the timer task will + * not run again. + * + *

This method may be called repeatedly; the second and subsequent + * calls have no effect. + * + * @return true if this task is scheduled for one-time execution and has + * not yet run, or this task is scheduled for repeated execution. + * Returns false if the task was scheduled for one-time execution + * and has already run, or if the task was never scheduled, or if + * the task was already cancelled. (Loosely speaking, this method + * returns true if it prevents one or more scheduled + * executions from taking place.) + */ + public boolean cancel() { + synchronized(lock) { + boolean result = (state == SCHEDULED); + state = CANCELLED; + return result; + } + } + + /** + * Returns the scheduled execution time of the most recent + * actual execution of this task. (If this method is invoked + * while task execution is in progress, the return value is the scheduled + * execution time of the ongoing task execution.) + * + *

This method is typically invoked from within a task's run method, to + * determine whether the current execution of the task is sufficiently + * timely to warrant performing the scheduled activity: + *

+     *   public void run() {
+     *       if (System.currentTimeMillis() - scheduledExecutionTime() >=
+     *           MAX_TARDINESS)
+     *               return;  // Too late; skip this execution.
+     *       // Perform the task
+     *   }
+     *

+ * This method is typically not used in conjunction with + * fixed-delay execution repeating tasks, as their scheduled + * execution times are allowed to drift over time, and so are not terribly + * significant. + * + * @return the time at which the most recent execution of this task was + * scheduled to occur, in the format returned by Date.getTime(). + * The return value is undefined if the task has yet to commence + * its first execution. + * @see Date#getTime() + */ + public long scheduledExecutionTime() { + synchronized(lock) { + return (period < 0 ? nextExecutionTime + period + : nextExecutionTime - period); + } + } +}