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package com.splout.db.common;

/*
 * #%L
 * Splout SQL commons
 * %%
 * Copyright (C) 2012 Datasalt Systems S.L.
 * %%
 * Licensed 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.
 * #L%
 */

import java.util.Iterator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;

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

import com.almworks.sqlite4java.SQLiteConnection;
import com.almworks.sqlite4java.SQLiteException;

/**
 * A Thread that is in charge of killing long-running queries.
 * TODO Generalize to other than sqlite 
 */
public class TimeoutThread extends Thread {

	private final static Log log = LogFactory.getLog(TimeoutThread.class);

	private ConcurrentHashMap currentQueries = new ConcurrentHashMap();
	private CopyOnWriteArrayList connections = new CopyOnWriteArrayList();
	
	private long timeout;

	static class QueryAndTime {
		String query;
		Long time;

		public QueryAndTime(String query, Long time) {
			this.query = query;
			this.time = time;
		}
	}

	/**
	 * @param timeout
	 *          The timeout in milliseconds. If a SQLite connection monitored by this Thread has a query that runs for
	 *          more than this, it will be interrupted and the query will return an error.
	 */
	public TimeoutThread(long timeout) {
		this.timeout = timeout;
	}

	@Override
	public void run() {
		log.info("Starting Timeout Thread...");
		try {
			while(true) {
				long now = System.currentTimeMillis();
				Iterator it = connections.iterator();
				while(it.hasNext()) {
					SQLiteConnection conn = it.next();
					QueryAndTime queryAndTime = currentQueries.get(conn);
					long time = queryAndTime.time;
					if(time < 0) { // means this connection is not active
						continue;
					}
					synchronized(conn) {
						if((now - time) > timeout) {
							// Timeout: we should interrupt this connection!

							try {

								/*
								 * Even though SQLiteConnections are not thread-safe, this method *IS* thread-safe and that's why we can
								 * implement this thread. The thread that launched the query is busy waiting for the result so another
								 * thread must interrupt it!
								 * 
								 * SQLite4Java docs:
								 * http://almworks.com/sqlite4java/javadoc/com/almworks/sqlite4java/SQLiteConnection.html#interrupt()
								 * SQLite docs: http://www.sqlite.org/c3ref/interrupt.html
								 */
								log.info("Long running query [" + queryAndTime.query + "] ran for more than ["
								    + timeout + "] ms. Interrupting it!");
								conn.interrupt();
							} catch(SQLiteException e) {
								//
							} finally {
								queryAndTime.query = null;
								queryAndTime.time = -1l; // connection will not be considered until a new query is executed
							}
						}
					}
				}
				long andNow = System.currentTimeMillis();
				if((andNow - now) < 1000) {
					Thread.sleep(1000 - (andNow - now));
				}
			}
		} catch(InterruptedException e) {
			log.info("Interrupted!");
		}
	}

	/**
	 * A Thread provides its thread-local connection to be monitored when a query starts. The SQL query is provided just
	 * for logging purposes.
	 */
	public void startQuery(SQLiteConnection connection, String query) {
		synchronized(connection) {
			if(!connections.contains(connection)) {
				connections.add(connection);
			}
			QueryAndTime qAndTime = currentQueries.get(connection);
			if(qAndTime == null) {
				qAndTime = new QueryAndTime(query, System.currentTimeMillis());
				currentQueries.put(connection, qAndTime);
			} else {
				qAndTime.query = query;
				qAndTime.time = System.currentTimeMillis();
			}
		}
	}

	/**
	 * The same Thread that provided this connection in startQuery() removes it from the monitoring list. So it is
	 * important to understand that this class makes the assumption that each SQLite Thread will use only one connection
	 * (Thread-local). {@link SQLite4JavaManager} behaves like this.
	 */
	public void endQuery(SQLiteConnection connection) {
		synchronized(connection) {
			QueryAndTime qAndTime = currentQueries.get(connection);
			if(qAndTime == null) {
				return;
			} else {
				qAndTime.query = null;
				qAndTime.time = -1l; // connection will not be considered until a new query is executed
			}
		}
	}

	// --- package-access getters for unit testing --- //
	
	ConcurrentHashMap getCurrentQueries() {
  	return currentQueries;
  }
	CopyOnWriteArrayList getConnections() {
  	return connections;
  }
}