[streaming] javadoc added to fault tolerance buffer

flink-addons/flink-streaming/src/main/java/eu/stratosphere/streaming/api/FaultTolerancyBuffer.java

@@ -26,10 +26,13 @@ import java.util.TreeMap;
 
 import eu.stratosphere.nephele.io.RecordWriter;
 
+/** An object to provide fault tolerance for Stratosphere stream processing.
+ * It works as a buffer to hold StreamRecords for a task for re-emitting failed, or timed out records.
+ */
 public class FaultTolerancyBuffer {
 
 	private long TIMEOUT = 1000;
-
+	
 	private Long timeOfLastUpdate;
 	private Map<String, StreamRecord> recordBuffer;
 	private Map<String, Integer> ackCounter;
@@ -41,6 +44,13 @@ public class FaultTolerancyBuffer {
 
 	private int numberOfOutputs;
 
+	/**Creates fault tolerance buffer object for the given output channels and channel ID
+	 * 
+	 * @param outputs
+	 * List of outputs
+	 * @param channelID
+	 * ID of the task object that uses this buffer
+	 */
 	public FaultTolerancyBuffer(List<RecordWriter<StreamRecord>> outputs,
 			String channelID) {
 		this.timeOfLastUpdate = System.currentTimeMillis();
@@ -53,6 +63,9 @@ public class FaultTolerancyBuffer {
 		this.recordTimestamps = new HashMap<String, Long>();
 	}
 
+/** Adds the record to the fault tolerance buffer. This record will be monitored for acknowledgements and timeout.
+ * 
+ */
 	public void addRecord(StreamRecord streamRecord) {
 
 		recordBuffer.put(streamRecord.getId(), streamRecord);
@@ -60,6 +73,13 @@ public class FaultTolerancyBuffer {
 		addTimestamp(streamRecord.getId());
 	}
 
+	/** Checks for records that have timed out since the last check and fails them.
+	 * 
+	 * @param currentTime
+	 * Time when the check should be made, usually current system time.
+	 * @return
+	 * Returns the list of the records that have timed out.
+	 */
 	List<String> timeoutRecords(Long currentTime) {
 		if (timeOfLastUpdate + TIMEOUT < currentTime) {
 			List<String> timedOutRecords = new LinkedList<String>();
@@ -85,6 +105,14 @@ public class FaultTolerancyBuffer {
 		return null;
 	}
 
+	/**Stores time stamp for a record by recordID 
+	 * and also adds the record to a map which maps a time stamp to the IDs of records that were emitted at that time.
+	 * <p>
+	 * Later used for timeouts.
+	 * 
+	 * @param recordID
+	 * ID of the record
+	 */
 	public void addTimestamp(String recordID) {
 		Long currentTime = System.currentTimeMillis();
 		recordTimestamps.put(recordID, currentTime);
@@ -98,6 +126,11 @@ public class FaultTolerancyBuffer {
 		}
 	}
 
+	/**Returns a StreamRecord after removing it from the buffer
+	 * 
+	 * @param recordID
+	 * 	   The ID of the record that will be popped
+	 */
 	public StreamRecord popRecord(String recordID) {
 		System.out.println("Pop ID: " + recordID);
 		StreamRecord record = recordBuffer.get(recordID);
@@ -105,6 +138,11 @@ public class FaultTolerancyBuffer {
 		return record;
 	}
 
+	/** Removes a StreamRecord by ID from the fault tolerance buffer, further acks will have no effects for this record.
+	 * @param recordID
+	 *        The ID of the record that will be removed
+	 * 
+	 */
 	void removeRecord(String recordID) {
 		recordBuffer.remove(recordID);
 		ackCounter.remove(recordID);
@@ -119,6 +157,11 @@ public class FaultTolerancyBuffer {
 		}
 	}
 
+	/**Acknowledges the record of the given ID, if all the outputs have sent acknowledgments, removes it from the buffer
+	 * 
+	 * @param recordID
+	 * ID of the record that has been acknowledged
+	 */
 	//TODO: find a place to call timeoutRecords
 	public void ackRecord(String recordID) {
 		if (ackCounter.containsKey(recordID)) {
@@ -133,6 +176,11 @@ public class FaultTolerancyBuffer {
 		//timeoutRecords(System.currentTimeMillis());
 	}
 
+	/**Re-emits the failed record for the given ID, removes the old record and stores it with a new ID.
+	 * 
+	 * @param recordID
+	 * ID of the record that has been failed
+	 */
 	public void failRecord(String recordID) {
 		// Create new id to avoid double counting acks
 		System.out.println("Fail ID: " + recordID);
@@ -140,7 +188,12 @@ public class FaultTolerancyBuffer {
 		addRecord(newRecord);
 		reEmit(newRecord);
 	}
-
+	
+/**
+ * Emit give record to all output channels
+ * @param record
+ * Record to be re-emitted
+ */
 	public void reEmit(StreamRecord record) {
 		for (RecordWriter<StreamRecord> output : outputs) {
 			try {