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| 1 | /* | ||
| 2 | * Copyright (c) 1999, 2004, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * A task that can be scheduled for one-time or repeated execution by a Timer. | ||
| 30 | * | ||
| 31 | * @author Josh Bloch | ||
| 32 | * @see Timer | ||
| 33 | * @since 1.3 | ||
| 34 | */ | ||
| 35 | |||
| 36 | public abstract class TimerTask implements Runnable { | ||
| 37 | /** | ||
| 38 | * This object is used to control access to the TimerTask internals. | ||
| 39 | */ | ||
| 40 | final Object lock = new Object(); | ||
| 41 | |||
| 42 | /** | ||
| 43 | * The state of this task, chosen from the constants below. | ||
| 44 | */ | ||
| 45 | int state = VIRGIN; | ||
| 46 | |||
| 47 | /** | ||
| 48 | * This task has not yet been scheduled. | ||
| 49 | */ | ||
| 50 | static final int VIRGIN = 0; | ||
| 51 | |||
| 52 | /** | ||
| 53 | * This task is scheduled for execution. If it is a non-repeating task, | ||
| 54 | * it has not yet been executed. | ||
| 55 | */ | ||
| 56 | static final int SCHEDULED = 1; | ||
| 57 | |||
| 58 | /** | ||
| 59 | * This non-repeating task has already executed (or is currently | ||
| 60 | * executing) and has not been cancelled. | ||
| 61 | */ | ||
| 62 | static final int EXECUTED = 2; | ||
| 63 | |||
| 64 | /** | ||
| 65 | * This task has been cancelled (with a call to TimerTask.cancel). | ||
| 66 | */ | ||
| 67 | static final int CANCELLED = 3; | ||
| 68 | |||
| 69 | /** | ||
| 70 | * Next execution time for this task in the format returned by | ||
| 71 | * System.currentTimeMillis, assuming this task is scheduled for execution. | ||
| 72 | * For repeating tasks, this field is updated prior to each task execution. | ||
| 73 | */ | ||
| 74 | long nextExecutionTime; | ||
| 75 | |||
| 76 | /** | ||
| 77 | * Period in milliseconds for repeating tasks. A positive value indicates | ||
| 78 | * fixed-rate execution. A negative value indicates fixed-delay execution. | ||
| 79 | * A value of 0 indicates a non-repeating task. | ||
| 80 | */ | ||
| 81 | long period = 0; | ||
| 82 | |||
| 83 | /** | ||
| 84 | * Creates a new timer task. | ||
| 85 | */ | ||
| 86 | protected TimerTask() { | ||
| 87 | } | ||
| 88 | |||
| 89 | /** | ||
| 90 | * The action to be performed by this timer task. | ||
| 91 | */ | ||
| 92 | public abstract void run(); | ||
| 93 | |||
| 94 | /** | ||
| 95 | * Cancels this timer task. If the task has been scheduled for one-time | ||
| 96 | * execution and has not yet run, or has not yet been scheduled, it will | ||
| 97 | * never run. If the task has been scheduled for repeated execution, it | ||
| 98 | * will never run again. (If the task is running when this call occurs, | ||
| 99 | * the task will run to completion, but will never run again.) | ||
| 100 | * | ||
| 101 | * <p>Note that calling this method from within the <tt>run</tt> method of | ||
| 102 | * a repeating timer task absolutely guarantees that the timer task will | ||
| 103 | * not run again. | ||
| 104 | * | ||
| 105 | * <p>This method may be called repeatedly; the second and subsequent | ||
| 106 | * calls have no effect. | ||
| 107 | * | ||
| 108 | * @return true if this task is scheduled for one-time execution and has | ||
| 109 | * not yet run, or this task is scheduled for repeated execution. | ||
| 110 | * Returns false if the task was scheduled for one-time execution | ||
| 111 | * and has already run, or if the task was never scheduled, or if | ||
| 112 | * the task was already cancelled. (Loosely speaking, this method | ||
| 113 | * returns <tt>true</tt> if it prevents one or more scheduled | ||
| 114 | * executions from taking place.) | ||
| 115 | */ | ||
| 116 | public boolean cancel() { | ||
| 117 | synchronized(lock) { | ||
| 118 | boolean result = (state == SCHEDULED); | ||
| 119 | state = CANCELLED; | ||
| 120 | return result; | ||
| 121 | } | ||
| 122 | } | ||
| 123 | |||
| 124 | /** | ||
| 125 | * Returns the <i>scheduled</i> execution time of the most recent | ||
| 126 | * <i>actual</i> execution of this task. (If this method is invoked | ||
| 127 | * while task execution is in progress, the return value is the scheduled | ||
| 128 | * execution time of the ongoing task execution.) | ||
| 129 | * | ||
| 130 | * <p>This method is typically invoked from within a task's run method, to | ||
| 131 | * determine whether the current execution of the task is sufficiently | ||
| 132 | * timely to warrant performing the scheduled activity: | ||
| 133 | * <pre> | ||
| 134 | * public void run() { | ||
| 135 | * if (System.currentTimeMillis() - scheduledExecutionTime() >= | ||
| 136 | * MAX_TARDINESS) | ||
| 137 | * return; // Too late; skip this execution. | ||
| 138 | * // Perform the task | ||
| 139 | * } | ||
| 140 | * </pre> | ||
| 141 | * This method is typically <i>not</i> used in conjunction with | ||
| 142 | * <i>fixed-delay execution</i> repeating tasks, as their scheduled | ||
| 143 | * execution times are allowed to drift over time, and so are not terribly | ||
| 144 | * significant. | ||
| 145 | * | ||
| 146 | * @return the time at which the most recent execution of this task was | ||
| 147 | * scheduled to occur, in the format returned by Date.getTime(). | ||
| 148 | * The return value is undefined if the task has yet to commence | ||
| 149 | * its first execution. | ||
| 150 | * @see Date#getTime() | ||
| 151 | */ | ||
| 152 | public long scheduledExecutionTime() { | ||
| 153 | synchronized(lock) { | ||
| 154 | return (period < 0 ? nextExecutionTime + period | ||
| 155 | : nextExecutionTime - period); | ||
| 156 | } | ||
| 157 | } | ||
| 158 | } | ||