[GitHub] [beam] lukecwik commented on a change in pull request #11735: [BEAM-2939] Ensure that watermark advances even when no elements are output.

[GitBox <gi...@apache.org>]

lukecwik commented on a change in pull request #11735:
URL: https://github.com/apache/beam/pull/11735#discussion_r426195050



##########
File path: sdks/java/core/src/main/java/org/apache/beam/sdk/io/Read.java
##########
@@ -487,51 +493,54 @@ public void splitRestriction(
 
     @NewTracker
     public RestrictionTracker<
-            KV<UnboundedSource<OutputT, CheckpointT>, CheckpointT>, UnboundedSourceValue<OutputT>[]>
+            UnboundedSourceRestriction<OutputT, CheckpointT>, UnboundedSourceValue<OutputT>[]>
         restrictionTracker(
-            @Restriction KV<UnboundedSource<OutputT, CheckpointT>, CheckpointT> restriction,
+            @Restriction UnboundedSourceRestriction<OutputT, CheckpointT> restriction,
             PipelineOptions pipelineOptions) {
       return new UnboundedSourceAsSDFRestrictionTracker(restriction, pipelineOptions);
     }
 
     @ProcessElement
     public ProcessContinuation processElement(
-        RestrictionTracker<
-                KV<UnboundedSource<OutputT, CheckpointT>, CheckpointT>, UnboundedSourceValue[]>
+        RestrictionTracker<UnboundedSourceRestriction<OutputT, CheckpointT>, UnboundedSourceValue[]>
             tracker,
         ManualWatermarkEstimator<Instant> watermarkEstimator,
         OutputReceiver<ValueWithRecordId<OutputT>> receiver,
         BundleFinalizer bundleFinalizer)
         throws IOException {
-      KV<UnboundedSource<OutputT, CheckpointT>, CheckpointT> initialRestriction =
+      UnboundedSourceRestriction<OutputT, CheckpointT> initialRestriction =
           tracker.currentRestriction();
 
       UnboundedSourceValue<OutputT>[] out = new UnboundedSourceValue[1];
       while (tracker.tryClaim(out)) {
         receiver.outputWithTimestamp(
             new ValueWithRecordId<>(out[0].getValue(), out[0].getId()), out[0].getTimestamp());
-        watermarkEstimator.setWatermark(ensureTimestampWithinBounds(out[0].getWatermark()));
       }
 
+      UnboundedSourceRestriction<OutputT, CheckpointT> currentRestriction =
+          tracker.currentRestriction();
+
+      // Advance the watermark even if zero elements may have been output.

Review comment:
       This is the key part of the change here, moving `watermarkEstimator.setWatermark` out of the while loop.




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