content: /*
   * 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.flink.translation.functions;
  
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.sdk.values.WindowedValues;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables;
  import org.apache.flink.api.common.state.ListState;
  import org.apache.flink.api.common.state.ListStateDescriptor;
  import org.apache.flink.api.common.typeutils.base.BooleanSerializer;
  import org.apache.flink.runtime.state.FunctionInitializationContext;
  import org.apache.flink.runtime.state.FunctionSnapshotContext;
  import org.apache.flink.streaming.api.checkpoint.CheckpointedFunction;
  import org.apache.flink.streaming.api.functions.source.SourceFunction;
  import org.apache.flink.streaming.api.watermark.Watermark;
  
  /**
   * Source function which sends a single global impulse to a downstream operator. It may keep the
   * source alive although its work is already done. It will only shutdown when the streaming job is
   * cancelled.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class ImpulseSourceFunction
      implements SourceFunction<WindowedValue<byte[]>>, CheckpointedFunction {
  
    /** The idle time before the source shuts down. */
    private final long idleTimeoutMs;
  
    /** Indicates the streaming job is running and the source can produce elements. */
    private volatile boolean running;
  
    /** Checkpointed state which indicates whether the impulse has finished. */
    private transient ListState<Boolean> impulseEmitted;
  
    public ImpulseSourceFunction(long idleTimeoutMs) {
      this.idleTimeoutMs = idleTimeoutMs;
      this.running = true;
    }
  
    @Override
    public void run(SourceContext<WindowedValue<byte[]>> sourceContext) throws Exception {
      if (Iterables.isEmpty(impulseEmitted.get())) {
        synchronized (sourceContext.getCheckpointLock()) {
          // emit single impulse element
          sourceContext.collect(WindowedValues.valueInGlobalWindow(new byte[0]));
          impulseEmitted.add(true);
        }
      }
      // Always emit a final watermark.
      // (1) In case we didn't restore the pipeline, this is important to close the global window;
      // if no operator holds back this watermark.
      // (2) In case we are restoring the pipeline, this is needed to initialize the operators with
      // the current watermark and trigger execution of any pending timers.
      sourceContext.emitWatermark(Watermark.MAX_WATERMARK);
      // Wait to allow checkpoints of the pipeline
      waitToEnsureCheckpointingWorksCorrectly();
    }
  
    private void waitToEnsureCheckpointingWorksCorrectly() {
      // Do nothing, but still look busy ...
      // we can't return here since Flink requires that all operators stay up,
      // otherwise checkpointing would not work correctly anymore
      //
      // See https://issues.apache.org/jira/browse/FLINK-2491 for progress on this issue
      long idleStart = System.currentTimeMillis();
      // wait until this is canceled
      final Object waitLock = new Object();
      while (running && (System.currentTimeMillis() - idleStart < idleTimeoutMs)) {
        try {
          // Flink will interrupt us at some point
          //noinspection SynchronizationOnLocalVariableOrMethodParameter
          synchronized (waitLock) {
            // don't wait indefinitely, in case something goes horribly wrong
            waitLock.wait(1000);
          }
        } catch (InterruptedException e) {
          if (!running) {
            // restore the interrupted state, and fall through the loop
            Thread.currentThread().interrupt();
          }
        }
      }
    }
  
    @Override
    public void cancel() {
      this.running = false;
    }
  
    @Override
    public void snapshotState(FunctionSnapshotContext context) {}
  
    @Override
    public void initializeState(FunctionInitializationContext context) throws Exception {
      impulseEmitted =
          context
              .getOperatorStateStore()
              .getListState(new ListStateDescriptor<>("impulse-emitted", BooleanSerializer.INSTANCE));
    }
  }
  