java.util.TimerTask Maven / Gradle / Ivy

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package java.util;

/**
 * The {@code TimerTask} class represents a task to run at a specified time. The task
 * may be run once or repeatedly.
 *
 * @see Timer
 * @see java.lang.Object#wait(long)
 */
public abstract class TimerTask implements Runnable {
    /* Lock object for synchronization. It's also used by Timer class. */
    final Object lock = new Object();

    /* If timer was cancelled */
    boolean cancelled;

    /* Slots used by Timer */
    long when;

    long period;

    boolean fixedRate;

    /*
     * The time when task will be executed, or the time when task was launched
     * if this is task in progress.
     */
    private long scheduledTime;

    /*
     * Method called from the Timer for synchronized getting of when field.
     */
    long getWhen() {
        synchronized (lock) {
            return when;
        }
    }

    /*
     * Method called from the Timer object when scheduling an event @param time
     */
    void setScheduledTime(long time) {
        synchronized (lock) {
            scheduledTime = time;
        }
    }

    /*
     * Is TimerTask scheduled into any timer?
     *
     * @return {@code true} if the timer task is scheduled, {@code false}
     * otherwise.
     */
    boolean isScheduled() {
        synchronized (lock) {
            return when > 0 || scheduledTime > 0;
        }
    }

    /**
     * Creates a new {@code TimerTask}.
     */
    protected TimerTask() {
    }

    /**
     * Cancels the {@code TimerTask} and removes it from the {@code Timer}'s queue. Generally, it
     * returns {@code false} if the call did not prevent a {@code TimerTask} from running at
     * least once. Subsequent calls have no effect.
     *
     * @return {@code true} if the call prevented a scheduled execution
     *         from taking place, {@code false} otherwise.
     */
    public boolean cancel() {
        synchronized (lock) {
            boolean willRun = !cancelled && when > 0;
            cancelled = true;
            return willRun;
        }
    }

    /**
     * Returns the scheduled execution time. If the task execution is in
     * progress it returns the execution time of the ongoing task. Tasks which
     * have not yet run return an undefined value.
     *
     * @return the most recent execution time.
     */
    public long scheduledExecutionTime() {
        synchronized (lock) {
            return scheduledTime;
        }
    }

    /**
     * The task to run should be specified in the implementation of the {@code run()}
     * method.
     */
    public abstract void run();

}