moodle-sync-app/moodle-sync-core/src/main/java/moodle/sync/core/util/ShutdownHandler.java

/*
 * Copyright (C) 2020 TU Darmstadt, Department of Computer Science,
 * Embedded Systems and Applications Group.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package moodle.sync.core.util;

import static java.util.Objects.requireNonNull;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public abstract class ShutdownHandler {

    private final static Logger LOG = LogManager.getLogger(ShutdownHandler.class);

    private final Lock lock = new ReentrantLock();

    private final Condition condition = lock.newCondition();


    /**
     * Executes specific code during the shutdown procedure, or throws an exception if unable to do so.
     *
     * @return {@code true} to execute next ShutdownHandler, {@code true} to stop the shutdown procedure.
     *
     * @throws Exception if unable to execute code.
     */
    abstract public boolean execute() throws Exception;


    protected void executeAndWait(Runnable runnable) {
        lock.lock();

        try {
            runnable.run();

            condition.await();
        }
        catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        finally {
            lock.unlock();
        }
    }

    protected void resume() {
        lock.lock();

        try {
            condition.signal();
        }
        finally {
            lock.unlock();
        }
    }

    final protected void logException(Throwable throwable, String throwMessage) {
        requireNonNull(throwable);
        requireNonNull(throwMessage);

        LOG.error(throwMessage, throwable);
    }
}