/**
* 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.camel.component.mongodb;
import com.mongodb.BasicDBObject;
import com.mongodb.Bytes;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MongoException.CursorNotFound;
import org.apache.camel.Exchange;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class MongoDbTailingProcess implements Runnable {
private static final Logger LOG = LoggerFactory.getLogger(MongoDbTailingProcess.class);
private static final String CAPPED_KEY = "capped";
public volatile boolean keepRunning = true;
public volatile boolean stopped; // = false
private final DBCollection dbCol;
private final MongoDbEndpoint endpoint;
private final MongoDbTailableCursorConsumer consumer;
// create local, final copies of these variables for increased performance
private final long cursorRegenerationDelay;
private final boolean cursorRegenerationDelayEnabled;
private DBCursor cursor;
private MongoDbTailTrackingManager tailTracking;
public MongoDbTailingProcess(MongoDbEndpoint endpoint, MongoDbTailableCursorConsumer consumer, MongoDbTailTrackingManager tailTrack) {
this.endpoint = endpoint;
this.consumer = consumer;
this.dbCol = endpoint.getDbCollection();
this.tailTracking = tailTrack;
this.cursorRegenerationDelay = endpoint.getCursorRegenerationDelay();
this.cursorRegenerationDelayEnabled = !(this.cursorRegenerationDelay == 0);
}
public DBCursor getCursor() {
return cursor;
}
/**
* Initialise the tailing process, the cursor and if persistent tail tracking is enabled, recover the cursor from the persisted point.
* As part of the initialisation process, the component will validate that the collection we are targeting is 'capped'.
* @throws Exception
*/
public void initializeProcess() throws Exception {
if (LOG.isInfoEnabled()) {
LOG.info("Starting MongoDB Tailable Cursor consumer, binding to collection: {}", "db: " + dbCol.getDB() + ", col: " + dbCol.getName());
}
if (dbCol.getStats().getInt(CAPPED_KEY) != 1) {
throw new CamelMongoDbException("Tailable cursors are only compatible with capped collections, and collection " + dbCol.getName()
+ " is not capped");
}
try {
// recover the last value from the store if it exists
tailTracking.recoverFromStore();
cursor = initializeCursor();
} catch (Exception e) {
throw new CamelMongoDbException("Exception ocurred while initializing tailable cursor", e);
}
if (cursor == null) {
throw new CamelMongoDbException("Tailable cursor was not initialized, or cursor returned is dead on arrival");
}
}
/**
* The heart of the tailing process.
*/
@Override
public void run() {
while (keepRunning) {
doRun();
// if the previous call didn't return because we have stopped running, then regenerate the cursor
if (keepRunning) {
cursor.close();
if (LOG.isDebugEnabled()) {
LOG.debug("Regenerating cursor with lastVal: {}, waiting {}ms first", tailTracking.lastVal, cursorRegenerationDelay);
}
if (cursorRegenerationDelayEnabled) {
try {
Thread.sleep(cursorRegenerationDelay);
} catch (InterruptedException e) {
LOG.error("Thread was interrupted", e);
}
}
cursor = initializeCursor();
}
}
stopped = true;
}
protected void stop() throws Exception {
if (LOG.isInfoEnabled()) {
LOG.info("Stopping MongoDB Tailable Cursor consumer, bound to collection: {}", "db: " + dbCol.getDB() + ", col: " + dbCol.getName());
}
keepRunning = false;
// close the cursor if it's open, so if it is blocked on hasNext() it will return immediately
if (cursor != null) {
cursor.close();
}
// wait until the main loop acknowledges the stop
while (!stopped) { }
if (LOG.isInfoEnabled()) {
LOG.info("Stopped MongoDB Tailable Cursor consumer, bound to collection: {}", "db: " + dbCol.getDB() + ", col: " + dbCol.getName());
}
}
/**
* The heart of the tailing process.
*/
private void doRun() {
// while the cursor has more values, keepRunning is true and the cursorId is not 0, which symbolizes that the cursor is dead
try {
while (cursor.hasNext() && cursor.getCursorId() != 0 && keepRunning) {
DBObject dbObj = cursor.next();
Exchange exchange = endpoint.createMongoDbExchange(dbObj);
try {
if (LOG.isTraceEnabled()) {
LOG.trace("Sending exchange: {}, ObjectId: {}", exchange, dbObj.get("_id"));
}
consumer.getProcessor().process(exchange);
} catch (Exception e) {
// do nothing
}
tailTracking.setLastVal(dbObj);
}
} catch (CursorNotFound e) {
// we only log the warning if we are not stopping, otherwise it is expected because the stop() method kills the cursor just in case it is blocked
// waiting for more data to arrive
if (keepRunning) {
LOG.debug("Cursor not found exception from MongoDB, will regenerate cursor. This is normal behaviour with tailable cursors.", e);
}
} catch (NullPointerException e) {
// The MongoDB Java Driver throws this uncontrolled NPE when the cursor is closed while blocked at DBCursor#hasMore.
// See https://jira.mongodb.org/browse/JAVA-605
}
// the loop finished, persist the lastValue just in case we are shutting down
// TODO: perhaps add a functionality to persist every N records
tailTracking.persistToStore();
}
// no arguments, will ask DB what the last updated Id was (checking persistent storage)
private DBCursor initializeCursor() {
Object lastVal = tailTracking.lastVal;
// lastVal can be null if we are initializing and there is no persistence enabled
DBCursor answer;
if (lastVal == null) {
answer = dbCol.find().addOption(Bytes.QUERYOPTION_TAILABLE).addOption(Bytes.QUERYOPTION_AWAITDATA);
} else {
DBObject queryObj = new BasicDBObject(tailTracking.getIncreasingFieldName(), new BasicDBObject("$gt", lastVal));
answer = dbCol.find(queryObj).addOption(Bytes.QUERYOPTION_TAILABLE).addOption(Bytes.QUERYOPTION_AWAITDATA);
}
return answer;
}
}