BatchProcessTimerExample.java

/*
 * 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 example;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.coders.Coder;
import org.apache.beam.sdk.coders.ListCoder;
import org.apache.beam.sdk.coders.VarLongCoder;
import org.apache.beam.sdk.options.PipelineOptions;
import org.apache.beam.sdk.options.PipelineOptionsFactory;
import org.apache.beam.sdk.state.StateSpec;
import org.apache.beam.sdk.state.StateSpecs;
import org.apache.beam.sdk.state.TimeDomain;
import org.apache.beam.sdk.state.Timer;
import org.apache.beam.sdk.state.TimerSpec;
import org.apache.beam.sdk.state.TimerSpecs;
import org.apache.beam.sdk.state.ValueState;
import org.apache.beam.sdk.transforms.Create;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.ParDo;
import org.apache.beam.sdk.transforms.WithKeys;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.MoreObjects;
import org.joda.time.Duration;
import org.joda.time.Instant;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class BatchProcessTimerExample {

  public static void main(String[] args) {
    PipelineOptions options = PipelineOptionsFactory.fromArgs(args).withValidation().as(PipelineOptions.class);
    Pipeline pipeline = Pipeline.create(options);
    pipeline
        .apply(Create.of(Stream.iterate(0L, i -> i + 1).limit(1000).collect(Collectors.toList())))
        .apply(WithKeys.of(0L))
        .apply(useEventTimeAsTimer(VarLongCoder.of(), Duration.standardSeconds(1L)))
        .apply(Log.of());

    pipeline.run();
  }

  private static <T> ParDo.SingleOutput<KV<Long, T>, T> useEventTimeAsTimer(
      Coder<T> coder, Duration interval) {
    return ParDo.of(new UseEventTimeAsTimerFn<>(coder, interval));
  }

  private static class UseEventTimeAsTimerFn<T> extends DoFn<KV<Long, T>, T> {
    private static final String TIMER_ID = "timerId";
    private static final String QUEUE_ID = "queue";
    private static final String RECORDED_TIMER_TIMESTAMP_ID = "recordedTimerTimestamp";

    @TimerId(TIMER_ID)
    private final TimerSpec timerSpec = TimerSpecs.timer(TimeDomain.PROCESSING_TIME);

    @StateId(QUEUE_ID)
    private final StateSpec<ValueState<List<T>>> queueStateSpec;

    @StateId(RECORDED_TIMER_TIMESTAMP_ID)
    private final StateSpec<ValueState<Long>> recordedTimerTimestampStateSpec = StateSpecs.value();

    private final Duration interval;

    private UseEventTimeAsTimerFn(Coder<T> coder, Duration interval) {
      queueStateSpec = StateSpecs.value(ListCoder.of(coder));
      this.interval = interval;
    }

    @ProcessElement
    public void process(
        @Element KV<Long, T> element,
        @Timestamp Instant elementTimestamp,
        @StateId(QUEUE_ID) ValueState<List<T>> queueState,
        @TimerId(TIMER_ID) Timer timer,
        @StateId(RECORDED_TIMER_TIMESTAMP_ID) ValueState<Long> recordedTimerTimestampState) {
      List<T> queue = MoreObjects.firstNonNull(queueState.read(), new ArrayList<>());
      queue.add(element.getValue());
      queueState.write(queue);
      if (recordedTimerTimestampState.read() == null) {
        timer.offset(interval).setRelative();
        recordedTimerTimestampState.write(timer.getCurrentRelativeTime().getMillis());
      }
    }

    @OnTimer(TIMER_ID)
    public void onTimer(
        @TimerId(TIMER_ID) Timer timer,
        @StateId(QUEUE_ID) ValueState<List<T>> queueState,
        @StateId(RECORDED_TIMER_TIMESTAMP_ID) ValueState<Long> recordedTimerTimestampState,
        OutputReceiver<T> receiver) {
      List<T> queue = MoreObjects.firstNonNull(queueState.read(), new ArrayList<>());
      if (queue.isEmpty()) {
        timer.clear();
        return;
      }

      receiver.output(queue.remove(0));
      queueState.write(queue);

      if (queue.isEmpty()) {
        return;
      }

      timer.offset(interval).setRelative();
      recordedTimerTimestampState.write(timer.getCurrentRelativeTime().getMillis());
    }
  }

  private static class Log {
    private static final Logger LOG = LoggerFactory.getLogger(Log.class);
    private static final Instant START = Instant.now();

    static <T> ParDo.SingleOutput<T, T> of() {
      return ParDo.of(new Log.Fn<>());
    }

    private static class Fn<T> extends DoFn<T, T> {
      @ProcessElement
      public void process(@Element T t, OutputReceiver<T> receiver) {
        Duration elapsed = Duration.millis(Instant.now().getMillis() - START.getMillis());
        LOG.info("{}: {}", elapsed, t);
        receiver.output(t);
      }
    }
  }
}

Running this example on both local and Dataflow runners has no output.