Github user Parth-Brahmbhatt commented on a diff in the pull request:
https://github.com/apache/storm/pull/900#discussion_r47559536
--- Diff:
storm-core/src/jvm/backtype/storm/windowing/WaterMarkEventGenerator.java ---
@@ -0,0 +1,110 @@
+/**
+ * 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 backtype.storm.windowing;
+
+import backtype.storm.generated.GlobalStreamId;
+import backtype.storm.topology.FailedException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Tracks tuples across input streams and periodically emits watermark
events.
+ * Watermark event timestamp is the minimum of the latest tuple timestamps
+ * across all the input streams (minus the lag). Once a watermark event is
emitted
+ * any tuple coming with an earlier timestamp can be considered as late
events.
+ */
+public class WaterMarkEventGenerator<T> implements Runnable {
+ private static final Logger LOG =
LoggerFactory.getLogger(WaterMarkEventGenerator.class);
+ private final WindowManager<T> windowManager;
+ private final int eventTsLag;
+ private final Set<GlobalStreamId> inputStreams;
+ private final Map<GlobalStreamId, Long> streamToTs;
+ private final ScheduledExecutorService executorService;
+ private final ScheduledFuture<?> executorFuture;
+ private long lastWaterMarkTs = 0;
+
+ public WaterMarkEventGenerator(WindowManager<T> windowManager, int
interval,
+ int eventTsLag, Set<GlobalStreamId>
inputStreams) {
+ this.windowManager = windowManager;
+ streamToTs = new ConcurrentHashMap<>();
+ executorService = Executors.newSingleThreadScheduledExecutor();
+ this.executorFuture = executorService.scheduleAtFixedRate(this,
interval, interval, TimeUnit.MILLISECONDS);
+ this.eventTsLag = eventTsLag;
+ this.inputStreams = inputStreams;
+ }
+
+ public void track(GlobalStreamId stream, long ts) {
+ Long currentVal = streamToTs.get(stream);
+ if (currentVal == null || ts > currentVal) {
+ streamToTs.put(stream, ts);
+ }
+ checkFailures();
+ }
+
+ @Override
+ public void run() {
+ try {
+ long waterMarkTs = computeWaterMarkTs();
+ if (waterMarkTs > lastWaterMarkTs) {
+ this.windowManager.add(new WaterMarkEvent<T>(waterMarkTs -
eventTsLag));
+ lastWaterMarkTs = waterMarkTs;
+ }
+ } catch (Throwable th) {
+ LOG.error("Failed while processing watermark event ", th);
+ throw th;
+ }
+ }
+
+ /**
+ * Computes the min ts across all streams.
+ */
+ private long computeWaterMarkTs() {
+ long ts = Long.MIN_VALUE;
+ // only if some data has arrived on each input stream
--- End diff --
why do we have to wait for data to arrive on each input stream?
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