SchedulerThread.java

/*
 * 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 org.apache.ode.scheduler.simple;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.ode.utils.stl.CollectionsX;
import org.apache.ode.utils.stl.MemberOfFunction;

/**
 * Implements the "todo" queue and prioritized scheduling mechanism. 
 * 
 * @author mszefler
 * @author Maciej Szefler ( m s z e f l e r @ g m a i l . c o m )
 * 
 */
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<Task> _todo;

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

	private Condition _activity = _lock.newCondition();

	private volatile boolean _done;

	private TaskRunner _taskrunner;

	private Thread _thread;

	SchedulerThread(TaskRunner runner) {
		_todo = new PriorityBlockingQueue<Task>(TODO_QUEUE_INITIAL_CAPACITY,
				new JobComparatorByDate());
		_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 job
	 */
	void enqueue(Task task) {
		_lock.lock();
		try {
			_todo.add(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 {
				long nextjob;
				while ((nextjob = nextJobTime()) > 0 && !_done)
					_activity.await(nextjob, TimeUnit.MILLISECONDS);

				if (!_done && nextjob == 0) {
					Task 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
	 */
	private long nextJobTime() {
		assert _lock.isLocked();

		Task 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 Task> tasktype) {
		_lock.lock();
		try {
			CollectionsX.remove_if(_todo, new MemberOfFunction<Task>() {
				@Override
				public boolean isMember(Task o) {
					return tasktype.isAssignableFrom(o.getClass());
				}

			});
		} finally {
			_lock.unlock();
		}
	}
}