junaiddshaukat commented on code in PR #39249: URL: https://github.com/apache/beam/pull/39249#discussion_r3546769860
########## runners/kafka-streams/src/main/java/org/apache/beam/runners/kafka/streams/translation/ReadProcessor.java: ########## @@ -0,0 +1,205 @@ +/* + * 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.beam.runners.kafka.streams.translation; + +import java.io.IOException; +import java.time.Duration; +import org.apache.beam.sdk.coders.Coder; +import org.apache.beam.sdk.coders.CoderException; +import org.apache.beam.sdk.io.BoundedSource; +import org.apache.beam.sdk.io.BoundedSource.BoundedReader; +import org.apache.beam.sdk.options.PipelineOptions; +import org.apache.beam.sdk.transforms.windowing.BoundedWindow; +import org.apache.beam.sdk.util.CoderUtils; +import org.apache.beam.sdk.values.WindowedValue; +import org.apache.beam.sdk.values.WindowedValues; +import org.apache.kafka.streams.processor.Cancellable; +import org.apache.kafka.streams.processor.PunctuationType; +import org.apache.kafka.streams.processor.api.Processor; +import org.apache.kafka.streams.processor.api.ProcessorContext; +import org.apache.kafka.streams.processor.api.Record; +import org.apache.kafka.streams.state.KeyValueStore; +import org.checkerframework.checker.nullness.qual.Nullable; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Kafka Streams {@link Processor} implementing Beam's deprecated primitive {@code Read} + * (beam:transform:read:v1) over a {@link BoundedSource}. + * + * <p>For each task instance, reads the whole {@link BoundedSource} once and emits, in order: + * + * <ol> + * <li>One {@link KStreamsPayload#data data} payload per source element, each wrapping a {@link + * WindowedValue} in the {@link org.apache.beam.sdk.transforms.windowing.GlobalWindow} at the + * element's own event time (from {@link BoundedReader#getCurrentTimestamp()}). + * <li>A {@link KStreamsPayload#watermark watermark} payload at {@link + * BoundedWindow#TIMESTAMP_MAX_VALUE} telling downstream transforms the source is done. + * </ol> + * + * <p><b>Wire form.</b> Unlike Impulse (whose element is already an opaque {@code byte[]}), a Read + * produces <em>decoded</em> Java objects. Downstream {@link ExecutableStageProcessor} feeds + * whatever it receives straight into the SDK harness, whose main-input receiver expects each + * element in the runner-side wire form — a raw object for a model coder, but a length-prefixed + * {@code byte[]} for a coder the runner does not know (e.g. {@code VarIntCoder}). Stage-to-stage + * edges already carry that wire form because harness outputs are decoded with the runner-side wire + * coder; this processor reproduces it for the source edge by transcoding each element through the + * SDK-side wire coder (encode) and back through the runner-side wire coder (decode). The two are + * byte-compatible by construction, so the transcode yields exactly the object the receiver expects, + * nesting and all. + * + * <p>This mirrors {@link ImpulseProcessor}: a persistent state store records whether the elements + * have already been emitted so task restarts do not duplicate them, while the terminal watermark is + * re-emitted on every restart so downstream watermark holds still release after recovery. The + * trigger is a wall-clock punctuator scheduled on {@link #init} so the processor fires even though + * its bootstrap source topic is empty. + * + * <p>The source is read in a single instance with no splitting — parallelism across the source's + * splits arrives with the topic-based shuffle work (#18479). Kafka Streams disallows negative + * record timestamps, so each forwarded {@link Record} carries the Unix epoch ({@code 0L}); the Beam + * event time lives inside the {@link WindowedValue}. + */ +class ReadProcessor<T> implements Processor<byte[], byte[], byte[], KStreamsPayload<?>> { + + private static final Logger LOG = LoggerFactory.getLogger(ReadProcessor.class); + + /** Sole entry in the state store; the value tracks whether this processor has already emitted. */ + static final String FIRED_KEY = "fired"; + + /** How soon after {@link #init} the punctuator first fires. */ + private static final Duration PUNCTUATION_DELAY = Duration.ofMillis(50); + + private final BoundedSource<T> source; + private final PipelineOptions options; + // Encodes a raw WindowedValue<T> as the SDK harness would on the wire (length-prefixing the + // element coder if the runner does not know it); the runner-side coder then decodes it into the + // wire form the downstream stage's input receiver expects. See the class javadoc. + private final Coder<WindowedValue<T>> sdkWireCoder; + private final Coder<WindowedValue<?>> runnerWireCoder; + private final String stateStoreName; + private final String transformId; + + private @Nullable ProcessorContext<byte[], KStreamsPayload<?>> context; + private @Nullable KeyValueStore<String, Boolean> firedStore; + private @Nullable Cancellable scheduledPunctuator; + + ReadProcessor( + BoundedSource<T> source, + PipelineOptions options, Review Comment: Done. One note, the class is org.apache.beam.runners.core.construction.SerializablePipelineOptions, not sdk.options. Worth flagging that KS builds the topology per instance and doesn't serialize processor suppliers, so this wasn't a live NotSerializableException, but the wrapper is cheap and keeps the captured state serializable. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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