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JDBC driver for MariaDB and MySQL for java 7
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/*
 *
 * MariaDB Client for Java
 *
 * Copyright (c) 2012-2014 Monty Program Ab.
 * Copyright (c) 2015-2017 MariaDB Ab.
 *
 * This library is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 *
 * This library 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 Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along
 * with this library; if not, write to Monty Program Ab [email protected].
 *
 * This particular MariaDB Client for Java file is work
 * derived from a Drizzle-JDBC. Drizzle-JDBC file which is covered by subject to
 * the following copyright and notice provisions:
 *
 * Copyright (c) 2009-2011, Marcus Eriksson
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * Redistributions of source code must retain the above copyright notice, this list
 * of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice, this
 * list of conditions and the following disclaimer in the documentation and/or
 * other materials provided with the distribution.
 *
 * Neither the name of the driver nor the names of its contributors may not be
 * used to endorse or promote products derived from this software without specific
 * prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS  AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 */

package org.mariadb.jdbc.internal.failover.thread;

import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.LockSupport;

public abstract class TerminableRunnable implements Runnable {

    private final AtomicReference runState = new AtomicReference<>(State.IDLE);
    private final AtomicBoolean unschedule = new AtomicBoolean();
    private volatile ScheduledFuture scheduledFuture = null;

    public TerminableRunnable(ScheduledExecutorService scheduler,
                              long initialDelay,
                              long delay,
                              TimeUnit unit) {
        this.scheduledFuture = scheduler.scheduleWithFixedDelay(this, initialDelay, delay, unit);
    }

    protected abstract void doRun();

    @Override
    public final void run() {
        if (!runState.compareAndSet(State.IDLE, State.ACTIVE)) {
            // task has somehow either started to run in parallel (should not be possible)
            // or more likely the task has now been set to terminate
            return;
        }
        try {
            doRun();
        } finally {
            runState.compareAndSet(State.ACTIVE, State.IDLE);
        }
    }

    /**
     * Unschedule next launched, and wait for the current task to complete before closing it.
     */
    public void blockTillTerminated() {
        while (!runState.compareAndSet(State.IDLE, State.REMOVED)) {
            // wait and retry
            LockSupport.parkNanos(TimeUnit.MILLISECONDS.toNanos(10));
            if (Thread.currentThread().isInterrupted()) {
                runState.set(State.REMOVED);
                return;
            }
        }
    }

    public boolean isUnschedule() {
        return unschedule.get();
    }

    /**
     * Unschedule task if active, and cancel thread to inform it must be interrupted in a proper way.
     */
    public void unscheduleTask() {
        if (unschedule.compareAndSet(false, true)) {
            scheduledFuture.cancel(false);
            scheduledFuture = null;
        }

    }

    private enum State {
        REMOVED,
        IDLE,
        ACTIVE
    }

}