jtulach@1405: /*
jtulach@1405:  * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved.
jtulach@1405:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jtulach@1405:  *
jtulach@1405:  * This code is free software; you can redistribute it and/or modify it
jtulach@1405:  * under the terms of the GNU General Public License version 2 only, as
jtulach@1405:  * published by the Free Software Foundation.  Oracle designates this
jtulach@1405:  * particular file as subject to the "Classpath" exception as provided
jtulach@1405:  * by Oracle in the LICENSE file that accompanied this code.
jtulach@1405:  *
jtulach@1405:  * This code is distributed in the hope that it will be useful, but WITHOUT
jtulach@1405:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jtulach@1405:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jtulach@1405:  * version 2 for more details (a copy is included in the LICENSE file that
jtulach@1405:  * accompanied this code).
jtulach@1405:  *
jtulach@1405:  * You should have received a copy of the GNU General Public License version
jtulach@1405:  * 2 along with this work; if not, write to the Free Software Foundation,
jtulach@1405:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jtulach@1405:  *
jtulach@1405:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jtulach@1405:  * or visit www.oracle.com if you need additional information or have any
jtulach@1405:  * questions.
jtulach@1405:  */
jtulach@1405: 
jtulach@1405: package java.util;
jtulach@1405: import java.util.Date;
jtulach@1405: import java.util.concurrent.atomic.AtomicInteger;
jtulach@1405: 
jtulach@1405: /**
jtulach@1405:  * A facility for threads to schedule tasks for future execution in a
jtulach@1405:  * background thread.  Tasks may be scheduled for one-time execution, or for
jtulach@1405:  * repeated execution at regular intervals.
jtulach@1405:  *
jtulach@1405:  * <p>Corresponding to each <tt>Timer</tt> object is a single background
jtulach@1405:  * thread that is used to execute all of the timer's tasks, sequentially.
jtulach@1405:  * Timer tasks should complete quickly.  If a timer task takes excessive time
jtulach@1405:  * to complete, it "hogs" the timer's task execution thread.  This can, in
jtulach@1405:  * turn, delay the execution of subsequent tasks, which may "bunch up" and
jtulach@1405:  * execute in rapid succession when (and if) the offending task finally
jtulach@1405:  * completes.
jtulach@1405:  *
jtulach@1405:  * <p>After the last live reference to a <tt>Timer</tt> object goes away
jtulach@1405:  * <i>and</i> all outstanding tasks have completed execution, the timer's task
jtulach@1405:  * execution thread terminates gracefully (and becomes subject to garbage
jtulach@1405:  * collection).  However, this can take arbitrarily long to occur.  By
jtulach@1405:  * default, the task execution thread does not run as a <i>daemon thread</i>,
jtulach@1405:  * so it is capable of keeping an application from terminating.  If a caller
jtulach@1405:  * wants to terminate a timer's task execution thread rapidly, the caller
jtulach@1405:  * should invoke the timer's <tt>cancel</tt> method.
jtulach@1405:  *
jtulach@1405:  * <p>If the timer's task execution thread terminates unexpectedly, for
jtulach@1405:  * example, because its <tt>stop</tt> method is invoked, any further
jtulach@1405:  * attempt to schedule a task on the timer will result in an
jtulach@1405:  * <tt>IllegalStateException</tt>, as if the timer's <tt>cancel</tt>
jtulach@1405:  * method had been invoked.
jtulach@1405:  *
jtulach@1405:  * <p>This class is thread-safe: multiple threads can share a single
jtulach@1405:  * <tt>Timer</tt> object without the need for external synchronization.
jtulach@1405:  *
jtulach@1405:  * <p>This class does <i>not</i> offer real-time guarantees: it schedules
jtulach@1405:  * tasks using the <tt>Object.wait(long)</tt> method.
jtulach@1405:  *
jtulach@1405:  * <p>Java 5.0 introduced the {@code java.util.concurrent} package and
jtulach@1405:  * one of the concurrency utilities therein is the {@link
jtulach@1405:  * java.util.concurrent.ScheduledThreadPoolExecutor
jtulach@1405:  * ScheduledThreadPoolExecutor} which is a thread pool for repeatedly
jtulach@1405:  * executing tasks at a given rate or delay.  It is effectively a more
jtulach@1405:  * versatile replacement for the {@code Timer}/{@code TimerTask}
jtulach@1405:  * combination, as it allows multiple service threads, accepts various
jtulach@1405:  * time units, and doesn't require subclassing {@code TimerTask} (just
jtulach@1405:  * implement {@code Runnable}).  Configuring {@code
jtulach@1405:  * ScheduledThreadPoolExecutor} with one thread makes it equivalent to
jtulach@1405:  * {@code Timer}.
jtulach@1405:  *
jtulach@1405:  * <p>Implementation note: This class scales to large numbers of concurrently
jtulach@1405:  * scheduled tasks (thousands should present no problem).  Internally,
jtulach@1405:  * it uses a binary heap to represent its task queue, so the cost to schedule
jtulach@1405:  * a task is O(log n), where n is the number of concurrently scheduled tasks.
jtulach@1405:  *
jtulach@1405:  * <p>Implementation note: All constructors start a timer thread.
jtulach@1405:  *
jtulach@1405:  * @author  Josh Bloch
jtulach@1405:  * @see     TimerTask
jtulach@1405:  * @see     Object#wait(long)
jtulach@1405:  * @since   1.3
jtulach@1405:  */
jtulach@1405: 
jtulach@1405: public class Timer {
jtulach@1405:     /**
jtulach@1405:      * The timer task queue.  This data structure is shared with the timer
jtulach@1405:      * thread.  The timer produces tasks, via its various schedule calls,
jtulach@1405:      * and the timer thread consumes, executing timer tasks as appropriate,
jtulach@1405:      * and removing them from the queue when they're obsolete.
jtulach@1405:      */
jtulach@1405:     private final TaskQueue queue = new TaskQueue();
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * The timer thread.
jtulach@1405:      */
jtulach@1405:     private final TimerThread thread = new TimerThread(queue);
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * This object causes the timer's task execution thread to exit
jtulach@1405:      * gracefully when there are no live references to the Timer object and no
jtulach@1405:      * tasks in the timer queue.  It is used in preference to a finalizer on
jtulach@1405:      * Timer as such a finalizer would be susceptible to a subclass's
jtulach@1405:      * finalizer forgetting to call it.
jtulach@1405:      */
jtulach@1405:     private final Object threadReaper = new Object() {
jtulach@1405:         protected void finalize() throws Throwable {
jtulach@1405:             synchronized(queue) {
jtulach@1405:                 thread.newTasksMayBeScheduled = false;
jtulach@1405:                 queue.notify(); // In case queue is empty.
jtulach@1405:             }
jtulach@1405:         }
jtulach@1405:     };
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * This ID is used to generate thread names.
jtulach@1405:      */
jtulach@1405:     private final static AtomicInteger nextSerialNumber = new AtomicInteger(0);
jtulach@1405:     private static int serialNumber() {
jtulach@1405:         return nextSerialNumber.getAndIncrement();
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Creates a new timer.  The associated thread does <i>not</i>
jtulach@1405:      * {@linkplain Thread#setDaemon run as a daemon}.
jtulach@1405:      */
jtulach@1405:     public Timer() {
jtulach@1405:         this("Timer-" + serialNumber());
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Creates a new timer whose associated thread may be specified to
jtulach@1405:      * {@linkplain Thread#setDaemon run as a daemon}.
jtulach@1405:      * A daemon thread is called for if the timer will be used to
jtulach@1405:      * schedule repeating "maintenance activities", which must be
jtulach@1405:      * performed as long as the application is running, but should not
jtulach@1405:      * prolong the lifetime of the application.
jtulach@1405:      *
jtulach@1405:      * @param isDaemon true if the associated thread should run as a daemon.
jtulach@1405:      */
jtulach@1405:     public Timer(boolean isDaemon) {
jtulach@1405:         this("Timer-" + serialNumber(), isDaemon);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Creates a new timer whose associated thread has the specified name.
jtulach@1405:      * The associated thread does <i>not</i>
jtulach@1405:      * {@linkplain Thread#setDaemon run as a daemon}.
jtulach@1405:      *
jtulach@1405:      * @param name the name of the associated thread
jtulach@1405:      * @throws NullPointerException if {@code name} is null
jtulach@1405:      * @since 1.5
jtulach@1405:      */
jtulach@1405:     public Timer(String name) {
jtulach@1405:         thread.setName(name);
jtulach@1405:         thread.start();
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Creates a new timer whose associated thread has the specified name,
jtulach@1405:      * and may be specified to
jtulach@1405:      * {@linkplain Thread#setDaemon run as a daemon}.
jtulach@1405:      *
jtulach@1405:      * @param name the name of the associated thread
jtulach@1405:      * @param isDaemon true if the associated thread should run as a daemon
jtulach@1405:      * @throws NullPointerException if {@code name} is null
jtulach@1405:      * @since 1.5
jtulach@1405:      */
jtulach@1405:     public Timer(String name, boolean isDaemon) {
jtulach@1405:         thread.setName(name);
jtulach@1405:         thread.setDaemon(isDaemon);
jtulach@1405:         thread.start();
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedules the specified task for execution after the specified delay.
jtulach@1405:      *
jtulach@1405:      * @param task  task to be scheduled.
jtulach@1405:      * @param delay delay in milliseconds before task is to be executed.
jtulach@1405:      * @throws IllegalArgumentException if <tt>delay</tt> is negative, or
jtulach@1405:      *         <tt>delay + System.currentTimeMillis()</tt> is negative.
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} is null
jtulach@1405:      */
jtulach@1405:     public void schedule(TimerTask task, long delay) {
jtulach@1405:         if (delay < 0)
jtulach@1405:             throw new IllegalArgumentException("Negative delay.");
jtulach@1405:         sched(task, System.currentTimeMillis()+delay, 0);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedules the specified task for execution at the specified time.  If
jtulach@1405:      * the time is in the past, the task is scheduled for immediate execution.
jtulach@1405:      *
jtulach@1405:      * @param task task to be scheduled.
jtulach@1405:      * @param time time at which task is to be executed.
jtulach@1405:      * @throws IllegalArgumentException if <tt>time.getTime()</tt> is negative.
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} or {@code time} is null
jtulach@1405:      */
jtulach@1405:     public void schedule(TimerTask task, Date time) {
jtulach@1405:         sched(task, time.getTime(), 0);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedules the specified task for repeated <i>fixed-delay execution</i>,
jtulach@1405:      * beginning after the specified delay.  Subsequent executions take place
jtulach@1405:      * at approximately regular intervals separated by the specified period.
jtulach@1405:      *
jtulach@1405:      * <p>In fixed-delay execution, each execution is scheduled relative to
jtulach@1405:      * the actual execution time of the previous execution.  If an execution
jtulach@1405:      * is delayed for any reason (such as garbage collection or other
jtulach@1405:      * background activity), subsequent executions will be delayed as well.
jtulach@1405:      * In the long run, the frequency of execution will generally be slightly
jtulach@1405:      * lower than the reciprocal of the specified period (assuming the system
jtulach@1405:      * clock underlying <tt>Object.wait(long)</tt> is accurate).
jtulach@1405:      *
jtulach@1405:      * <p>Fixed-delay execution is appropriate for recurring activities
jtulach@1405:      * that require "smoothness."  In other words, it is appropriate for
jtulach@1405:      * activities where it is more important to keep the frequency accurate
jtulach@1405:      * in the short run than in the long run.  This includes most animation
jtulach@1405:      * tasks, such as blinking a cursor at regular intervals.  It also includes
jtulach@1405:      * tasks wherein regular activity is performed in response to human
jtulach@1405:      * input, such as automatically repeating a character as long as a key
jtulach@1405:      * is held down.
jtulach@1405:      *
jtulach@1405:      * @param task   task to be scheduled.
jtulach@1405:      * @param delay  delay in milliseconds before task is to be executed.
jtulach@1405:      * @param period time in milliseconds between successive task executions.
jtulach@1405:      * @throws IllegalArgumentException if {@code delay < 0}, or
jtulach@1405:      *         {@code delay + System.currentTimeMillis() < 0}, or
jtulach@1405:      *         {@code period <= 0}
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} is null
jtulach@1405:      */
jtulach@1405:     public void schedule(TimerTask task, long delay, long period) {
jtulach@1405:         if (delay < 0)
jtulach@1405:             throw new IllegalArgumentException("Negative delay.");
jtulach@1405:         if (period <= 0)
jtulach@1405:             throw new IllegalArgumentException("Non-positive period.");
jtulach@1405:         sched(task, System.currentTimeMillis()+delay, -period);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedules the specified task for repeated <i>fixed-delay execution</i>,
jtulach@1405:      * beginning at the specified time. Subsequent executions take place at
jtulach@1405:      * approximately regular intervals, separated by the specified period.
jtulach@1405:      *
jtulach@1405:      * <p>In fixed-delay execution, each execution is scheduled relative to
jtulach@1405:      * the actual execution time of the previous execution.  If an execution
jtulach@1405:      * is delayed for any reason (such as garbage collection or other
jtulach@1405:      * background activity), subsequent executions will be delayed as well.
jtulach@1405:      * In the long run, the frequency of execution will generally be slightly
jtulach@1405:      * lower than the reciprocal of the specified period (assuming the system
jtulach@1405:      * clock underlying <tt>Object.wait(long)</tt> is accurate).  As a
jtulach@1405:      * consequence of the above, if the scheduled first time is in the past,
jtulach@1405:      * it is scheduled for immediate execution.
jtulach@1405:      *
jtulach@1405:      * <p>Fixed-delay execution is appropriate for recurring activities
jtulach@1405:      * that require "smoothness."  In other words, it is appropriate for
jtulach@1405:      * activities where it is more important to keep the frequency accurate
jtulach@1405:      * in the short run than in the long run.  This includes most animation
jtulach@1405:      * tasks, such as blinking a cursor at regular intervals.  It also includes
jtulach@1405:      * tasks wherein regular activity is performed in response to human
jtulach@1405:      * input, such as automatically repeating a character as long as a key
jtulach@1405:      * is held down.
jtulach@1405:      *
jtulach@1405:      * @param task   task to be scheduled.
jtulach@1405:      * @param firstTime First time at which task is to be executed.
jtulach@1405:      * @param period time in milliseconds between successive task executions.
jtulach@1405:      * @throws IllegalArgumentException if {@code firstTime.getTime() < 0}, or
jtulach@1405:      *         {@code period <= 0}
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} or {@code firstTime} is null
jtulach@1405:      */
jtulach@1405:     public void schedule(TimerTask task, Date firstTime, long period) {
jtulach@1405:         if (period <= 0)
jtulach@1405:             throw new IllegalArgumentException("Non-positive period.");
jtulach@1405:         sched(task, firstTime.getTime(), -period);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedules the specified task for repeated <i>fixed-rate execution</i>,
jtulach@1405:      * beginning after the specified delay.  Subsequent executions take place
jtulach@1405:      * at approximately regular intervals, separated by the specified period.
jtulach@1405:      *
jtulach@1405:      * <p>In fixed-rate execution, each execution is scheduled relative to the
jtulach@1405:      * scheduled execution time of the initial execution.  If an execution is
jtulach@1405:      * delayed for any reason (such as garbage collection or other background
jtulach@1405:      * activity), two or more executions will occur in rapid succession to
jtulach@1405:      * "catch up."  In the long run, the frequency of execution will be
jtulach@1405:      * exactly the reciprocal of the specified period (assuming the system
jtulach@1405:      * clock underlying <tt>Object.wait(long)</tt> is accurate).
jtulach@1405:      *
jtulach@1405:      * <p>Fixed-rate execution is appropriate for recurring activities that
jtulach@1405:      * are sensitive to <i>absolute</i> time, such as ringing a chime every
jtulach@1405:      * hour on the hour, or running scheduled maintenance every day at a
jtulach@1405:      * particular time.  It is also appropriate for recurring activities
jtulach@1405:      * where the total time to perform a fixed number of executions is
jtulach@1405:      * important, such as a countdown timer that ticks once every second for
jtulach@1405:      * ten seconds.  Finally, fixed-rate execution is appropriate for
jtulach@1405:      * scheduling multiple repeating timer tasks that must remain synchronized
jtulach@1405:      * with respect to one another.
jtulach@1405:      *
jtulach@1405:      * @param task   task to be scheduled.
jtulach@1405:      * @param delay  delay in milliseconds before task is to be executed.
jtulach@1405:      * @param period time in milliseconds between successive task executions.
jtulach@1405:      * @throws IllegalArgumentException if {@code delay < 0}, or
jtulach@1405:      *         {@code delay + System.currentTimeMillis() < 0}, or
jtulach@1405:      *         {@code period <= 0}
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} is null
jtulach@1405:      */
jtulach@1405:     public void scheduleAtFixedRate(TimerTask task, long delay, long period) {
jtulach@1405:         if (delay < 0)
jtulach@1405:             throw new IllegalArgumentException("Negative delay.");
jtulach@1405:         if (period <= 0)
jtulach@1405:             throw new IllegalArgumentException("Non-positive period.");
jtulach@1405:         sched(task, System.currentTimeMillis()+delay, period);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedules the specified task for repeated <i>fixed-rate execution</i>,
jtulach@1405:      * beginning at the specified time. Subsequent executions take place at
jtulach@1405:      * approximately regular intervals, separated by the specified period.
jtulach@1405:      *
jtulach@1405:      * <p>In fixed-rate execution, each execution is scheduled relative to the
jtulach@1405:      * scheduled execution time of the initial execution.  If an execution is
jtulach@1405:      * delayed for any reason (such as garbage collection or other background
jtulach@1405:      * activity), two or more executions will occur in rapid succession to
jtulach@1405:      * "catch up."  In the long run, the frequency of execution will be
jtulach@1405:      * exactly the reciprocal of the specified period (assuming the system
jtulach@1405:      * clock underlying <tt>Object.wait(long)</tt> is accurate).  As a
jtulach@1405:      * consequence of the above, if the scheduled first time is in the past,
jtulach@1405:      * then any "missed" executions will be scheduled for immediate "catch up"
jtulach@1405:      * execution.
jtulach@1405:      *
jtulach@1405:      * <p>Fixed-rate execution is appropriate for recurring activities that
jtulach@1405:      * are sensitive to <i>absolute</i> time, such as ringing a chime every
jtulach@1405:      * hour on the hour, or running scheduled maintenance every day at a
jtulach@1405:      * particular time.  It is also appropriate for recurring activities
jtulach@1405:      * where the total time to perform a fixed number of executions is
jtulach@1405:      * important, such as a countdown timer that ticks once every second for
jtulach@1405:      * ten seconds.  Finally, fixed-rate execution is appropriate for
jtulach@1405:      * scheduling multiple repeating timer tasks that must remain synchronized
jtulach@1405:      * with respect to one another.
jtulach@1405:      *
jtulach@1405:      * @param task   task to be scheduled.
jtulach@1405:      * @param firstTime First time at which task is to be executed.
jtulach@1405:      * @param period time in milliseconds between successive task executions.
jtulach@1405:      * @throws IllegalArgumentException if {@code firstTime.getTime() < 0} or
jtulach@1405:      *         {@code period <= 0}
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} or {@code firstTime} is null
jtulach@1405:      */
jtulach@1405:     public void scheduleAtFixedRate(TimerTask task, Date firstTime,
jtulach@1405:                                     long period) {
jtulach@1405:         if (period <= 0)
jtulach@1405:             throw new IllegalArgumentException("Non-positive period.");
jtulach@1405:         sched(task, firstTime.getTime(), period);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Schedule the specified timer task for execution at the specified
jtulach@1405:      * time with the specified period, in milliseconds.  If period is
jtulach@1405:      * positive, the task is scheduled for repeated execution; if period is
jtulach@1405:      * zero, the task is scheduled for one-time execution. Time is specified
jtulach@1405:      * in Date.getTime() format.  This method checks timer state, task state,
jtulach@1405:      * and initial execution time, but not period.
jtulach@1405:      *
jtulach@1405:      * @throws IllegalArgumentException if <tt>time</tt> is negative.
jtulach@1405:      * @throws IllegalStateException if task was already scheduled or
jtulach@1405:      *         cancelled, timer was cancelled, or timer thread terminated.
jtulach@1405:      * @throws NullPointerException if {@code task} is null
jtulach@1405:      */
jtulach@1405:     private void sched(TimerTask task, long time, long period) {
jtulach@1405:         if (time < 0)
jtulach@1405:             throw new IllegalArgumentException("Illegal execution time.");
jtulach@1405: 
jtulach@1405:         // Constrain value of period sufficiently to prevent numeric
jtulach@1405:         // overflow while still being effectively infinitely large.
jtulach@1405:         if (Math.abs(period) > (Long.MAX_VALUE >> 1))
jtulach@1405:             period >>= 1;
jtulach@1405: 
jtulach@1405:         synchronized(queue) {
jtulach@1405:             if (!thread.newTasksMayBeScheduled)
jtulach@1405:                 throw new IllegalStateException("Timer already cancelled.");
jtulach@1405: 
jtulach@1405:             synchronized(task.lock) {
jtulach@1405:                 if (task.state != TimerTask.VIRGIN)
jtulach@1405:                     throw new IllegalStateException(
jtulach@1405:                         "Task already scheduled or cancelled");
jtulach@1405:                 task.nextExecutionTime = time;
jtulach@1405:                 task.period = period;
jtulach@1405:                 task.state = TimerTask.SCHEDULED;
jtulach@1405:             }
jtulach@1405: 
jtulach@1405:             queue.add(task);
jtulach@1405:             if (queue.getMin() == task)
jtulach@1405:                 queue.notify();
jtulach@1405:         }
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Terminates this timer, discarding any currently scheduled tasks.
jtulach@1405:      * Does not interfere with a currently executing task (if it exists).
jtulach@1405:      * Once a timer has been terminated, its execution thread terminates
jtulach@1405:      * gracefully, and no more tasks may be scheduled on it.
jtulach@1405:      *
jtulach@1405:      * <p>Note that calling this method from within the run method of a
jtulach@1405:      * timer task that was invoked by this timer absolutely guarantees that
jtulach@1405:      * the ongoing task execution is the last task execution that will ever
jtulach@1405:      * be performed by this timer.
jtulach@1405:      *
jtulach@1405:      * <p>This method may be called repeatedly; the second and subsequent
jtulach@1405:      * calls have no effect.
jtulach@1405:      */
jtulach@1405:     public void cancel() {
jtulach@1405:         synchronized(queue) {
jtulach@1405:             thread.newTasksMayBeScheduled = false;
jtulach@1405:             queue.clear();
jtulach@1405:             queue.notify();  // In case queue was already empty.
jtulach@1405:         }
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Removes all cancelled tasks from this timer's task queue.  <i>Calling
jtulach@1405:      * this method has no effect on the behavior of the timer</i>, but
jtulach@1405:      * eliminates the references to the cancelled tasks from the queue.
jtulach@1405:      * If there are no external references to these tasks, they become
jtulach@1405:      * eligible for garbage collection.
jtulach@1405:      *
jtulach@1405:      * <p>Most programs will have no need to call this method.
jtulach@1405:      * It is designed for use by the rare application that cancels a large
jtulach@1405:      * number of tasks.  Calling this method trades time for space: the
jtulach@1405:      * runtime of the method may be proportional to n + c log n, where n
jtulach@1405:      * is the number of tasks in the queue and c is the number of cancelled
jtulach@1405:      * tasks.
jtulach@1405:      *
jtulach@1405:      * <p>Note that it is permissible to call this method from within a
jtulach@1405:      * a task scheduled on this timer.
jtulach@1405:      *
jtulach@1405:      * @return the number of tasks removed from the queue.
jtulach@1405:      * @since 1.5
jtulach@1405:      */
jtulach@1405:      public int purge() {
jtulach@1405:          int result = 0;
jtulach@1405: 
jtulach@1405:          synchronized(queue) {
jtulach@1405:              for (int i = queue.size(); i > 0; i--) {
jtulach@1405:                  if (queue.get(i).state == TimerTask.CANCELLED) {
jtulach@1405:                      queue.quickRemove(i);
jtulach@1405:                      result++;
jtulach@1405:                  }
jtulach@1405:              }
jtulach@1405: 
jtulach@1405:              if (result != 0)
jtulach@1405:                  queue.heapify();
jtulach@1405:          }
jtulach@1405: 
jtulach@1405:          return result;
jtulach@1405:      }
jtulach@1405: }
jtulach@1405: 
jtulach@1405: /**
jtulach@1405:  * This "helper class" implements the timer's task execution thread, which
jtulach@1405:  * waits for tasks on the timer queue, executions them when they fire,
jtulach@1405:  * reschedules repeating tasks, and removes cancelled tasks and spent
jtulach@1405:  * non-repeating tasks from the queue.
jtulach@1405:  */
jtulach@1405: class TimerThread extends Thread {
jtulach@1405:     /**
jtulach@1405:      * This flag is set to false by the reaper to inform us that there
jtulach@1405:      * are no more live references to our Timer object.  Once this flag
jtulach@1405:      * is true and there are no more tasks in our queue, there is no
jtulach@1405:      * work left for us to do, so we terminate gracefully.  Note that
jtulach@1405:      * this field is protected by queue's monitor!
jtulach@1405:      */
jtulach@1405:     boolean newTasksMayBeScheduled = true;
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Our Timer's queue.  We store this reference in preference to
jtulach@1405:      * a reference to the Timer so the reference graph remains acyclic.
jtulach@1405:      * Otherwise, the Timer would never be garbage-collected and this
jtulach@1405:      * thread would never go away.
jtulach@1405:      */
jtulach@1405:     private TaskQueue queue;
jtulach@1405: 
jtulach@1405:     TimerThread(TaskQueue queue) {
jtulach@1405:         this.queue = queue;
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     public void run() {
jtulach@1405:         try {
jtulach@1405:             mainLoop();
jtulach@1405:         } finally {
jtulach@1405:             // Someone killed this Thread, behave as if Timer cancelled
jtulach@1405:             synchronized(queue) {
jtulach@1405:                 newTasksMayBeScheduled = false;
jtulach@1405:                 queue.clear();  // Eliminate obsolete references
jtulach@1405:             }
jtulach@1405:         }
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * The main timer loop.  (See class comment.)
jtulach@1405:      */
jtulach@1405:     private void mainLoop() {
jtulach@1405:         while (true) {
jtulach@1405:             try {
jtulach@1405:                 TimerTask task;
jtulach@1405:                 boolean taskFired;
jtulach@1405:                 synchronized(queue) {
jtulach@1405:                     // Wait for queue to become non-empty
jtulach@1405:                     while (queue.isEmpty() && newTasksMayBeScheduled)
jtulach@1405:                         queue.wait();
jtulach@1405:                     if (queue.isEmpty())
jtulach@1405:                         break; // Queue is empty and will forever remain; die
jtulach@1405: 
jtulach@1405:                     // Queue nonempty; look at first evt and do the right thing
jtulach@1405:                     long currentTime, executionTime;
jtulach@1405:                     task = queue.getMin();
jtulach@1405:                     synchronized(task.lock) {
jtulach@1405:                         if (task.state == TimerTask.CANCELLED) {
jtulach@1405:                             queue.removeMin();
jtulach@1405:                             continue;  // No action required, poll queue again
jtulach@1405:                         }
jtulach@1405:                         currentTime = System.currentTimeMillis();
jtulach@1405:                         executionTime = task.nextExecutionTime;
jtulach@1405:                         if (taskFired = (executionTime<=currentTime)) {
jtulach@1405:                             if (task.period == 0) { // Non-repeating, remove
jtulach@1405:                                 queue.removeMin();
jtulach@1405:                                 task.state = TimerTask.EXECUTED;
jtulach@1405:                             } else { // Repeating task, reschedule
jtulach@1405:                                 queue.rescheduleMin(
jtulach@1405:                                   task.period<0 ? currentTime   - task.period
jtulach@1405:                                                 : executionTime + task.period);
jtulach@1405:                             }
jtulach@1405:                         }
jtulach@1405:                     }
jtulach@1405:                     if (!taskFired) // Task hasn't yet fired; wait
jtulach@1405:                         queue.wait(executionTime - currentTime);
jtulach@1405:                 }
jtulach@1405:                 if (taskFired)  // Task fired; run it, holding no locks
jtulach@1405:                     task.run();
jtulach@1405:             } catch(InterruptedException e) {
jtulach@1405:             }
jtulach@1405:         }
jtulach@1405:     }
jtulach@1405: }
jtulach@1405: 
jtulach@1405: /**
jtulach@1405:  * This class represents a timer task queue: a priority queue of TimerTasks,
jtulach@1405:  * ordered on nextExecutionTime.  Each Timer object has one of these, which it
jtulach@1405:  * shares with its TimerThread.  Internally this class uses a heap, which
jtulach@1405:  * offers log(n) performance for the add, removeMin and rescheduleMin
jtulach@1405:  * operations, and constant time performance for the getMin operation.
jtulach@1405:  */
jtulach@1405: class TaskQueue {
jtulach@1405:     /**
jtulach@1405:      * Priority queue represented as a balanced binary heap: the two children
jtulach@1405:      * of queue[n] are queue[2*n] and queue[2*n+1].  The priority queue is
jtulach@1405:      * ordered on the nextExecutionTime field: The TimerTask with the lowest
jtulach@1405:      * nextExecutionTime is in queue[1] (assuming the queue is nonempty).  For
jtulach@1405:      * each node n in the heap, and each descendant of n, d,
jtulach@1405:      * n.nextExecutionTime <= d.nextExecutionTime.
jtulach@1405:      */
jtulach@1405:     private TimerTask[] queue = new TimerTask[128];
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * The number of tasks in the priority queue.  (The tasks are stored in
jtulach@1405:      * queue[1] up to queue[size]).
jtulach@1405:      */
jtulach@1405:     private int size = 0;
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Returns the number of tasks currently on the queue.
jtulach@1405:      */
jtulach@1405:     int size() {
jtulach@1405:         return size;
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Adds a new task to the priority queue.
jtulach@1405:      */
jtulach@1405:     void add(TimerTask task) {
jtulach@1405:         // Grow backing store if necessary
jtulach@1405:         if (size + 1 == queue.length)
jtulach@1405:             queue = Arrays.copyOf(queue, 2*queue.length);
jtulach@1405: 
jtulach@1405:         queue[++size] = task;
jtulach@1405:         fixUp(size);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Return the "head task" of the priority queue.  (The head task is an
jtulach@1405:      * task with the lowest nextExecutionTime.)
jtulach@1405:      */
jtulach@1405:     TimerTask getMin() {
jtulach@1405:         return queue[1];
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Return the ith task in the priority queue, where i ranges from 1 (the
jtulach@1405:      * head task, which is returned by getMin) to the number of tasks on the
jtulach@1405:      * queue, inclusive.
jtulach@1405:      */
jtulach@1405:     TimerTask get(int i) {
jtulach@1405:         return queue[i];
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Remove the head task from the priority queue.
jtulach@1405:      */
jtulach@1405:     void removeMin() {
jtulach@1405:         queue[1] = queue[size];
jtulach@1405:         queue[size--] = null;  // Drop extra reference to prevent memory leak
jtulach@1405:         fixDown(1);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Removes the ith element from queue without regard for maintaining
jtulach@1405:      * the heap invariant.  Recall that queue is one-based, so
jtulach@1405:      * 1 <= i <= size.
jtulach@1405:      */
jtulach@1405:     void quickRemove(int i) {
jtulach@1405:         assert i <= size;
jtulach@1405: 
jtulach@1405:         queue[i] = queue[size];
jtulach@1405:         queue[size--] = null;  // Drop extra ref to prevent memory leak
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Sets the nextExecutionTime associated with the head task to the
jtulach@1405:      * specified value, and adjusts priority queue accordingly.
jtulach@1405:      */
jtulach@1405:     void rescheduleMin(long newTime) {
jtulach@1405:         queue[1].nextExecutionTime = newTime;
jtulach@1405:         fixDown(1);
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Returns true if the priority queue contains no elements.
jtulach@1405:      */
jtulach@1405:     boolean isEmpty() {
jtulach@1405:         return size==0;
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Removes all elements from the priority queue.
jtulach@1405:      */
jtulach@1405:     void clear() {
jtulach@1405:         // Null out task references to prevent memory leak
jtulach@1405:         for (int i=1; i<=size; i++)
jtulach@1405:             queue[i] = null;
jtulach@1405: 
jtulach@1405:         size = 0;
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Establishes the heap invariant (described above) assuming the heap
jtulach@1405:      * satisfies the invariant except possibly for the leaf-node indexed by k
jtulach@1405:      * (which may have a nextExecutionTime less than its parent's).
jtulach@1405:      *
jtulach@1405:      * This method functions by "promoting" queue[k] up the hierarchy
jtulach@1405:      * (by swapping it with its parent) repeatedly until queue[k]'s
jtulach@1405:      * nextExecutionTime is greater than or equal to that of its parent.
jtulach@1405:      */
jtulach@1405:     private void fixUp(int k) {
jtulach@1405:         while (k > 1) {
jtulach@1405:             int j = k >> 1;
jtulach@1405:             if (queue[j].nextExecutionTime <= queue[k].nextExecutionTime)
jtulach@1405:                 break;
jtulach@1405:             TimerTask tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
jtulach@1405:             k = j;
jtulach@1405:         }
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Establishes the heap invariant (described above) in the subtree
jtulach@1405:      * rooted at k, which is assumed to satisfy the heap invariant except
jtulach@1405:      * possibly for node k itself (which may have a nextExecutionTime greater
jtulach@1405:      * than its children's).
jtulach@1405:      *
jtulach@1405:      * This method functions by "demoting" queue[k] down the hierarchy
jtulach@1405:      * (by swapping it with its smaller child) repeatedly until queue[k]'s
jtulach@1405:      * nextExecutionTime is less than or equal to those of its children.
jtulach@1405:      */
jtulach@1405:     private void fixDown(int k) {
jtulach@1405:         int j;
jtulach@1405:         while ((j = k << 1) <= size && j > 0) {
jtulach@1405:             if (j < size &&
jtulach@1405:                 queue[j].nextExecutionTime > queue[j+1].nextExecutionTime)
jtulach@1405:                 j++; // j indexes smallest kid
jtulach@1405:             if (queue[k].nextExecutionTime <= queue[j].nextExecutionTime)
jtulach@1405:                 break;
jtulach@1405:             TimerTask tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
jtulach@1405:             k = j;
jtulach@1405:         }
jtulach@1405:     }
jtulach@1405: 
jtulach@1405:     /**
jtulach@1405:      * Establishes the heap invariant (described above) in the entire tree,
jtulach@1405:      * assuming nothing about the order of the elements prior to the call.
jtulach@1405:      */
jtulach@1405:     void heapify() {
jtulach@1405:         for (int i = size/2; i >= 1; i--)
jtulach@1405:             fixDown(i);
jtulach@1405:     }
jtulach@1405: }