| /* |
| * Copyright (c) 1999, 2004, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.util; |
| |
| /** |
| * A task that can be scheduled for one-time or repeated execution by a Timer. |
| * |
| * @author Josh Bloch |
| * @see Timer |
| * @since 1.3 |
| */ |
| |
| public abstract class TimerTask implements Runnable { |
| /** |
| * This object is used to control access to the TimerTask internals. |
| */ |
| final Object lock = new Object(); |
| |
| /** |
| * The state of this task, chosen from the constants below. |
| */ |
| int state = VIRGIN; |
| |
| /** |
| * This task has not yet been scheduled. |
| */ |
| static final int VIRGIN = 0; |
| |
| /** |
| * This task is scheduled for execution. If it is a non-repeating task, |
| * it has not yet been executed. |
| */ |
| static final int SCHEDULED = 1; |
| |
| /** |
| * This non-repeating task has already executed (or is currently |
| * executing) and has not been cancelled. |
| */ |
| static final int EXECUTED = 2; |
| |
| /** |
| * This task has been cancelled (with a call to TimerTask.cancel). |
| */ |
| static final int CANCELLED = 3; |
| |
| /** |
| * Next execution time for this task in the format returned by |
| * System.currentTimeMillis, assuming this task is scheduled for execution. |
| * For repeating tasks, this field is updated prior to each task execution. |
| */ |
| long nextExecutionTime; |
| |
| /** |
| * Period in milliseconds for repeating tasks. A positive value indicates |
| * fixed-rate execution. A negative value indicates fixed-delay execution. |
| * A value of 0 indicates a non-repeating task. |
| */ |
| long period = 0; |
| |
| /** |
| * Creates a new timer task. |
| */ |
| protected TimerTask() { |
| } |
| |
| /** |
| * The action to be performed by this timer task. |
| */ |
| public abstract void run(); |
| |
| /** |
| * Cancels this timer task. If the task has been scheduled for one-time |
| * execution and has not yet run, or has not yet been scheduled, it will |
| * never run. If the task has been scheduled for repeated execution, it |
| * will never run again. (If the task is running when this call occurs, |
| * the task will run to completion, but will never run again.) |
| * |
| * <p>Note that calling this method from within the <tt>run</tt> method of |
| * a repeating timer task absolutely guarantees that the timer task will |
| * not run again. |
| * |
| * <p>This method may be called repeatedly; the second and subsequent |
| * calls have no effect. |
| * |
| * @return true if this task is scheduled for one-time execution and has |
| * not yet run, or this task is scheduled for repeated execution. |
| * Returns false if the task was scheduled for one-time execution |
| * and has already run, or if the task was never scheduled, or if |
| * the task was already cancelled. (Loosely speaking, this method |
| * returns <tt>true</tt> if it prevents one or more scheduled |
| * executions from taking place.) |
| */ |
| public boolean cancel() { |
| synchronized(lock) { |
| boolean result = (state == SCHEDULED); |
| state = CANCELLED; |
| return result; |
| } |
| } |
| |
| /** |
| * Returns the <i>scheduled</i> execution time of the most recent |
| * <i>actual</i> execution of this task. (If this method is invoked |
| * while task execution is in progress, the return value is the scheduled |
| * execution time of the ongoing task execution.) |
| * |
| * <p>This method is typically invoked from within a task's run method, to |
| * determine whether the current execution of the task is sufficiently |
| * timely to warrant performing the scheduled activity: |
| * <pre> |
| * public void run() { |
| * if (System.currentTimeMillis() - scheduledExecutionTime() >= |
| * MAX_TARDINESS) |
| * return; // Too late; skip this execution. |
| * // Perform the task |
| * } |
| * </pre> |
| * This method is typically <i>not</i> used in conjunction with |
| * <i>fixed-delay execution</i> repeating tasks, as their scheduled |
| * execution times are allowed to drift over time, and so are not terribly |
| * significant. |
| * |
| * @return the time at which the most recent execution of this task was |
| * scheduled to occur, in the format returned by Date.getTime(). |
| * The return value is undefined if the task has yet to commence |
| * its first execution. |
| * @see Date#getTime() |
| */ |
| public long scheduledExecutionTime() { |
| synchronized(lock) { |
| return (period < 0 ? nextExecutionTime + period |
| : nextExecutionTime - period); |
| } |
| } |
| } |