SchedulerThread.java

/*
 * Copyright (c) 2016, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 * WSO2 Inc. 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 org.wso2.carbon.bpmn.people.substitution.scheduler;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.util.Iterator;
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class SchedulerThread implements Runnable {
    private static final Log __log = LogFactory.getLog(SchedulerThread.class);

    private static final int TODO_QUEUE_INITIAL_CAPACITY = 200;

    /** Jobs ready for immediate execution. */
    private PriorityBlockingQueue<ScheduledTask> _todo;

    /** Lock for managing the queue */
    private ReentrantLock _lock = new ReentrantLock();

    private Condition _activity = _lock.newCondition();

    private volatile boolean _done;

    private ScheduledTaskRunner _taskrunner;

    private Thread _thread;

    SchedulerThread(ScheduledTaskRunner runner) {
        _todo = new PriorityBlockingQueue<ScheduledTask>(TODO_QUEUE_INITIAL_CAPACITY,
                new ComparatorByDate());
        _taskrunner = runner;
    }

    void start() {
        if (_thread != null)
            return;

        _done = false;
        _thread = new Thread(this, "OdeScheduler");
        _thread.start();
    }

    /**
     * Shutdown the thread.
     */
    void stop() {
        if (_thread == null)
            return;

        _done = true;
        _lock.lock();
        try {
            _activity.signal();
        } finally {
            _lock.unlock();

        }

        while (_thread != null)
            try {
                _thread.join();
                _thread = null;
            } catch (InterruptedException e) {
                ;
            }

    }

    /**
     * Add a job to the todo queue.
     *
     * @param task
     */
    void enqueue(ScheduledTask task) {
        _lock.lock();
        try {
            _todo.add(task);
            _activity.signal();
        } finally {
            _lock.unlock();
        }
    }

    /**
     * Remove a job to the todo queue.
     *
     * @param task
     */
    void dequeue(ScheduledTask task) {
        _lock.lock();
        try {
            _todo.remove(task);
            _activity.signal();
        } finally {
            _lock.unlock();
        }
    }

    /**
     * Get the size of the todo queue.
     *
     * @return
     */
    public int size() {
        return _todo.size();
    }

    /**
     * Pop items off the todo queue, and send them to the task runner for processing.
     */
    public void run() {
        while (!_done) {
            _lock.lock();
            try {
                boolean wait = false;
                long nextjob;
                while ((nextjob = nextJobTime()) > 0 && !_done)
                    wait = _activity.await(nextjob, TimeUnit.MILLISECONDS);
                    if (__log.isDebugEnabled()) {
                        __log.debug("waiting for next job : " + wait);
                    }

                if (!_done && nextjob == 0) {
                    ScheduledTask task = _todo.take();
                    _taskrunner.runTask(task);

                }
            } catch (InterruptedException ex) {
                ; // ignore
            } finally {
                _lock.unlock();
            }
        }
    }

    /**
     * Calculate the time until the next available job.
     *
     * @return time until next job, 0 if one is one is scheduled to go, and some
     *         really large number if there are no jobs to speak of
     */
    protected long nextJobTime() {
        assert _lock.isLocked();

        ScheduledTask job = _todo.peek();
        if (job == null)
            return Long.MAX_VALUE;

        return Math.max(0, job.schedDate - System.currentTimeMillis());
    }

    /**
     * Remove the tasks of a given type from the list.
     * @param taskType type of task
     */
    public void clearTasks(final Class<? extends ScheduledTask> taskType) {
        _lock.lock();
        try {
            Iterator<ScheduledTask> i = _todo.iterator();

            while (i.hasNext()) {
                if (taskType.isAssignableFrom(i.next().getClass())) {
                    i.remove();
                }
            }
        } finally {
            _lock.unlock();
        }
    }

}