739 lines
30 KiB
Java
739 lines
30 KiB
Java
/*
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* Copyright (c) 1999, 2021, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.util;
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import dalvik.annotation.optimization.ReachabilitySensitive;
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import java.util.Date;
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import java.util.concurrent.atomic.AtomicInteger;
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import java.lang.ref.Cleaner.Cleanable;
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import jdk.internal.ref.CleanerFactory;
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/**
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* A facility for threads to schedule tasks for future execution in a
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* background thread. Tasks may be scheduled for one-time execution, or for
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* repeated execution at regular intervals.
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*
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* <p>Corresponding to each {@code Timer} object is a single background
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* thread that is used to execute all of the timer's tasks, sequentially.
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* Timer tasks should complete quickly. If a timer task takes excessive time
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* to complete, it "hogs" the timer's task execution thread. This can, in
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* turn, delay the execution of subsequent tasks, which may "bunch up" and
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* execute in rapid succession when (and if) the offending task finally
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* completes.
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*
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* <p>After the last live reference to a {@code Timer} object goes away
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* <i>and</i> all outstanding tasks have completed execution, the timer's task
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* execution thread terminates gracefully (and becomes subject to garbage
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* collection). However, this can take arbitrarily long to occur. By
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* default, the task execution thread does not run as a <i>daemon thread</i>,
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* so it is capable of keeping an application from terminating. If a caller
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* wants to terminate a timer's task execution thread rapidly, the caller
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* should invoke the timer's {@code cancel} method.
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*
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* <p>If the timer's task execution thread terminates unexpectedly, for
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* example, because its {@code stop} method is invoked, any further
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* attempt to schedule a task on the timer will result in an
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* {@code IllegalStateException}, as if the timer's {@code cancel}
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* method had been invoked.
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*
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* <p>This class is thread-safe: multiple threads can share a single
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* {@code Timer} object without the need for external synchronization.
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*
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* <p>This class does <i>not</i> offer real-time guarantees: it schedules
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* tasks using the {@code Object.wait(long)} method.
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*
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* <p>Java 5.0 introduced the {@code java.util.concurrent} package and
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* one of the concurrency utilities therein is the {@link
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* java.util.concurrent.ScheduledThreadPoolExecutor
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* ScheduledThreadPoolExecutor} which is a thread pool for repeatedly
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* executing tasks at a given rate or delay. It is effectively a more
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* versatile replacement for the {@code Timer}/{@code TimerTask}
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* combination, as it allows multiple service threads, accepts various
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* time units, and doesn't require subclassing {@code TimerTask} (just
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* implement {@code Runnable}). Configuring {@code
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* ScheduledThreadPoolExecutor} with one thread makes it equivalent to
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* {@code Timer}.
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*
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* <p>Implementation note: This class scales to large numbers of concurrently
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* scheduled tasks (thousands should present no problem). Internally,
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* it uses a binary heap to represent its task queue, so the cost to schedule
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* a task is O(log n), where n is the number of concurrently scheduled tasks.
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*
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* <p>Implementation note: All constructors start a timer thread.
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*
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* @author Josh Bloch
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* @see TimerTask
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* @see Object#wait(long)
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* @since 1.3
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*/
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public class Timer {
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/**
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* The timer task queue. This data structure is shared with the timer
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* thread. The timer produces tasks, via its various schedule calls,
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* and the timer thread consumes, executing timer tasks as appropriate,
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* and removing them from the queue when they're obsolete.
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*/
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// Android-added: @ReachabilitySensitive
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// Otherwise the finalizer may cancel the Timer in the middle of a
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// sched() call.
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@ReachabilitySensitive
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private final TaskQueue queue = new TaskQueue();
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/**
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* The timer thread.
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*/
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// Android-added: @ReachabilitySensitive
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@ReachabilitySensitive
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private final TimerThread thread = new TimerThread(queue);
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/**
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* An object of this class is registered with a Cleaner as the cleanup
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* handler for this Timer object. This causes the execution thread to
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* exit gracefully when there are no live references to the Timer object
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* and no tasks in the timer queue.
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*/
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private static class ThreadReaper implements Runnable {
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private final TaskQueue queue;
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private final TimerThread thread;
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ThreadReaper(TaskQueue queue, TimerThread thread) {
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this.queue = queue;
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this.thread = thread;
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}
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public void run() {
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synchronized(queue) {
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thread.newTasksMayBeScheduled = false;
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queue.notify(); // In case queue is empty.
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}
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}
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}
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private final Cleanable cleanup;
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/**
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* This ID is used to generate thread names.
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*/
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private static final AtomicInteger nextSerialNumber = new AtomicInteger();
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private static int serialNumber() {
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return nextSerialNumber.getAndIncrement();
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}
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/**
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* Creates a new timer. The associated thread does <i>not</i>
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* {@linkplain Thread#setDaemon run as a daemon}.
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*/
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public Timer() {
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this("Timer-" + serialNumber());
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}
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/**
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* Creates a new timer whose associated thread may be specified to
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* {@linkplain Thread#setDaemon run as a daemon}.
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* A daemon thread is called for if the timer will be used to
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* schedule repeating "maintenance activities", which must be
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* performed as long as the application is running, but should not
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* prolong the lifetime of the application.
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*
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* @param isDaemon true if the associated thread should run as a daemon.
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*/
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public Timer(boolean isDaemon) {
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this("Timer-" + serialNumber(), isDaemon);
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}
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/**
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* Creates a new timer whose associated thread has the specified name.
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* The associated thread does <i>not</i>
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* {@linkplain Thread#setDaemon run as a daemon}.
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*
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* @param name the name of the associated thread
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* @throws NullPointerException if {@code name} is null
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* @since 1.5
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*/
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public Timer(String name) {
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this(name, false);
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}
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/**
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* Creates a new timer whose associated thread has the specified name,
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* and may be specified to
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* {@linkplain Thread#setDaemon run as a daemon}.
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*
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* @param name the name of the associated thread
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* @param isDaemon true if the associated thread should run as a daemon
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* @throws NullPointerException if {@code name} is null
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* @since 1.5
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*/
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public Timer(String name, boolean isDaemon) {
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var threadReaper = new ThreadReaper(queue, thread);
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this.cleanup = CleanerFactory.cleaner().register(this, threadReaper);
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thread.setName(name);
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thread.setDaemon(isDaemon);
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thread.start();
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}
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/**
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* Schedules the specified task for execution after the specified delay.
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*
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* @param task task to be scheduled.
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* @param delay delay in milliseconds before task is to be executed.
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* @throws IllegalArgumentException if {@code delay} is negative, or
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* {@code delay + System.currentTimeMillis()} is negative.
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* @throws IllegalStateException if task was already scheduled or
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} is null
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*/
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public void schedule(TimerTask task, long delay) {
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if (delay < 0)
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throw new IllegalArgumentException("Negative delay.");
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sched(task, System.currentTimeMillis()+delay, 0);
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}
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/**
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* Schedules the specified task for execution at the specified time. If
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* the time is in the past, the task is scheduled for immediate execution.
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*
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* @param task task to be scheduled.
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* @param time time at which task is to be executed.
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* @throws IllegalArgumentException if {@code time.getTime()} is negative.
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* @throws IllegalStateException if task was already scheduled or
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} or {@code time} is null
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*/
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public void schedule(TimerTask task, Date time) {
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sched(task, time.getTime(), 0);
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}
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/**
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* Schedules the specified task for repeated <i>fixed-delay execution</i>,
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* beginning after the specified delay. Subsequent executions take place
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* at approximately regular intervals separated by the specified period.
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*
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* <p>In fixed-delay execution, each execution is scheduled relative to
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* the actual execution time of the previous execution. If an execution
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* is delayed for any reason (such as garbage collection or other
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* background activity), subsequent executions will be delayed as well.
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* In the long run, the frequency of execution will generally be slightly
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* lower than the reciprocal of the specified period (assuming the system
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* clock underlying {@code Object.wait(long)} is accurate).
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*
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* <p>Fixed-delay execution is appropriate for recurring activities
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* that require "smoothness." In other words, it is appropriate for
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* activities where it is more important to keep the frequency accurate
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* in the short run than in the long run. This includes most animation
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* tasks, such as blinking a cursor at regular intervals. It also includes
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* tasks wherein regular activity is performed in response to human
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* input, such as automatically repeating a character as long as a key
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* is held down.
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*
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* @param task task to be scheduled.
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* @param delay delay in milliseconds before task is to be executed.
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* @param period time in milliseconds between successive task executions.
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* @throws IllegalArgumentException if {@code delay < 0}, or
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* {@code delay + System.currentTimeMillis() < 0}, or
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* {@code period <= 0}
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* @throws IllegalStateException if task was already scheduled or
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} is null
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*/
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public void schedule(TimerTask task, long delay, long period) {
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if (delay < 0)
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throw new IllegalArgumentException("Negative delay.");
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if (period <= 0)
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throw new IllegalArgumentException("Non-positive period.");
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sched(task, System.currentTimeMillis()+delay, -period);
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}
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/**
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* Schedules the specified task for repeated <i>fixed-delay execution</i>,
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* beginning at the specified time. Subsequent executions take place at
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* approximately regular intervals, separated by the specified period.
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*
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* <p>In fixed-delay execution, each execution is scheduled relative to
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* the actual execution time of the previous execution. If an execution
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* is delayed for any reason (such as garbage collection or other
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* background activity), subsequent executions will be delayed as well.
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* In the long run, the frequency of execution will generally be slightly
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* lower than the reciprocal of the specified period (assuming the system
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* clock underlying {@code Object.wait(long)} is accurate). As a
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* consequence of the above, if the scheduled first time is in the past,
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* it is scheduled for immediate execution.
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*
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* <p>Fixed-delay execution is appropriate for recurring activities
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* that require "smoothness." In other words, it is appropriate for
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* activities where it is more important to keep the frequency accurate
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* in the short run than in the long run. This includes most animation
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* tasks, such as blinking a cursor at regular intervals. It also includes
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* tasks wherein regular activity is performed in response to human
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* input, such as automatically repeating a character as long as a key
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* is held down.
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*
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* @param task task to be scheduled.
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* @param firstTime First time at which task is to be executed.
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* @param period time in milliseconds between successive task executions.
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* @throws IllegalArgumentException if {@code firstTime.getTime() < 0}, or
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* {@code period <= 0}
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* @throws IllegalStateException if task was already scheduled or
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} or {@code firstTime} is null
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*/
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public void schedule(TimerTask task, Date firstTime, long period) {
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if (period <= 0)
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throw new IllegalArgumentException("Non-positive period.");
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sched(task, firstTime.getTime(), -period);
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}
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/**
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* Schedules the specified task for repeated <i>fixed-rate execution</i>,
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* beginning after the specified delay. Subsequent executions take place
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* at approximately regular intervals, separated by the specified period.
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*
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* <p>In fixed-rate execution, each execution is scheduled relative to the
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* scheduled execution time of the initial execution. If an execution is
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* delayed for any reason (such as garbage collection or other background
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* activity), two or more executions will occur in rapid succession to
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* "catch up." In the long run, the frequency of execution will be
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* exactly the reciprocal of the specified period (assuming the system
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* clock underlying {@code Object.wait(long)} is accurate).
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*
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* <p>Fixed-rate execution is appropriate for recurring activities that
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* are sensitive to <i>absolute</i> time, such as ringing a chime every
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* hour on the hour, or running scheduled maintenance every day at a
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* particular time. It is also appropriate for recurring activities
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* where the total time to perform a fixed number of executions is
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* important, such as a countdown timer that ticks once every second for
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* ten seconds. Finally, fixed-rate execution is appropriate for
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* scheduling multiple repeating timer tasks that must remain synchronized
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* with respect to one another.
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*
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* @param task task to be scheduled.
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* @param delay delay in milliseconds before task is to be executed.
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* @param period time in milliseconds between successive task executions.
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* @throws IllegalArgumentException if {@code delay < 0}, or
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* {@code delay + System.currentTimeMillis() < 0}, or
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* {@code period <= 0}
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* @throws IllegalStateException if task was already scheduled or
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} is null
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*/
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public void scheduleAtFixedRate(TimerTask task, long delay, long period) {
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if (delay < 0)
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throw new IllegalArgumentException("Negative delay.");
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if (period <= 0)
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throw new IllegalArgumentException("Non-positive period.");
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sched(task, System.currentTimeMillis()+delay, period);
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}
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/**
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* Schedules the specified task for repeated <i>fixed-rate execution</i>,
|
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* beginning at the specified time. Subsequent executions take place at
|
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* approximately regular intervals, separated by the specified period.
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*
|
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* <p>In fixed-rate execution, each execution is scheduled relative to the
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* scheduled execution time of the initial execution. If an execution is
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* delayed for any reason (such as garbage collection or other background
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|
* activity), two or more executions will occur in rapid succession to
|
|
* "catch up." In the long run, the frequency of execution will be
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* exactly the reciprocal of the specified period (assuming the system
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* clock underlying {@code Object.wait(long)} is accurate). As a
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* consequence of the above, if the scheduled first time is in the past,
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* then any "missed" executions will be scheduled for immediate "catch up"
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* execution.
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*
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* <p>Fixed-rate execution is appropriate for recurring activities that
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* are sensitive to <i>absolute</i> time, such as ringing a chime every
|
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* hour on the hour, or running scheduled maintenance every day at a
|
|
* particular time. It is also appropriate for recurring activities
|
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* where the total time to perform a fixed number of executions is
|
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* important, such as a countdown timer that ticks once every second for
|
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* ten seconds. Finally, fixed-rate execution is appropriate for
|
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* scheduling multiple repeating timer tasks that must remain synchronized
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* with respect to one another.
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*
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* @param task task to be scheduled.
|
|
* @param firstTime First time at which task is to be executed.
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* @param period time in milliseconds between successive task executions.
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* @throws IllegalArgumentException if {@code firstTime.getTime() < 0} or
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* {@code period <= 0}
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* @throws IllegalStateException if task was already scheduled or
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} or {@code firstTime} is null
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*/
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public void scheduleAtFixedRate(TimerTask task, Date firstTime,
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long period) {
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if (period <= 0)
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throw new IllegalArgumentException("Non-positive period.");
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sched(task, firstTime.getTime(), period);
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}
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/**
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* Schedule the specified timer task for execution at the specified
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* time with the specified period, in milliseconds. If period is
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* positive, the task is scheduled for repeated execution; if period is
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* zero, the task is scheduled for one-time execution. Time is specified
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* in Date.getTime() format. This method checks timer state, task state,
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* and initial execution time, but not period.
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*
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* @throws IllegalArgumentException if {@code time} is negative.
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* @throws IllegalStateException if task was already scheduled or
|
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* cancelled, timer was cancelled, or timer thread terminated.
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* @throws NullPointerException if {@code task} is null
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*/
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private void sched(TimerTask task, long time, long period) {
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if (time < 0)
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throw new IllegalArgumentException("Illegal execution time.");
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|
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// Constrain value of period sufficiently to prevent numeric
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// overflow while still being effectively infinitely large.
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if (Math.abs(period) > (Long.MAX_VALUE >> 1))
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period >>= 1;
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synchronized(queue) {
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if (!thread.newTasksMayBeScheduled)
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throw new IllegalStateException("Timer already cancelled.");
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|
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synchronized(task.lock) {
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if (task.state != TimerTask.VIRGIN)
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throw new IllegalStateException(
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"Task already scheduled or cancelled");
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task.nextExecutionTime = time;
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task.period = period;
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task.state = TimerTask.SCHEDULED;
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}
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queue.add(task);
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if (queue.getMin() == task)
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queue.notify();
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}
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}
|
|
|
|
/**
|
|
* 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.
|
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*
|
|
* <p>Note that calling this method from within the run method of a
|
|
* timer task that was invoked by this timer absolutely guarantees that
|
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* the ongoing task execution is the last task execution that will ever
|
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* be performed by this timer.
|
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*
|
|
* <p>This method may be called repeatedly; the second and subsequent
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* calls have no effect.
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*/
|
|
public void cancel() {
|
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synchronized(queue) {
|
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queue.clear();
|
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cleanup.clean();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* 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 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);
|
|
}
|
|
}
|