runners/twister2/src/main/java/org/apache/beam/runners/twister2/translators/functions/ImpulseSource.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
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package org.apache.beam.runners.twister2.translators.functions;

import edu.iu.dsc.tws.api.tset.fn.SourceFunc;
import org.apache.beam.sdk.util.WindowedValue;

/** A {@link SourceFunc} which executes the impulse transform contract. */
public class ImpulseSource implements SourceFunc<WindowedValue<byte[]>> {
  private static final WindowedValue<byte[]> IMPULSE_VALUE =
      WindowedValue.valueInGlobalWindow(new byte[0]);

  private boolean impulseEmitted = false;

  @Override
  public boolean hasNext() {
    return !impulseEmitted;
  }

  @Override
  public WindowedValue<byte[]> next() {
    if (impulseEmitted) {
      throw new IllegalStateException("Impulse has already emitted an element.");
    }
    impulseEmitted = true;
    return IMPULSE_VALUE;
  }
}