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.dataflow.worker.streaming.harness;
  
  import javax.annotation.concurrent.ThreadSafe;
  import org.apache.beam.runners.dataflow.worker.windmill.WindmillEndpoints.Endpoint;
  import org.apache.beam.runners.dataflow.worker.windmill.client.WindmillStream.GetDataStream;
  import org.apache.beam.sdk.annotations.Internal;
  
  @Internal
  @ThreadSafe
  final class GlobalDataStreamSender implements StreamSender {
    private final Endpoint endpoint;
    private final GetDataStream delegate;
    private volatile boolean started;
  
    GlobalDataStreamSender(GetDataStream delegate, Endpoint endpoint) {
      this.delegate = delegate;
      this.started = false;
      this.endpoint = endpoint;
    }
  
    GetDataStream stream() {
      if (!started) {
        // Starting the stream possibly perform IO. Start the stream lazily since not all pipeline
        // implementations need to fetch global/side input data.
        startStream();
      }
  
      return delegate;
    }
  
    private synchronized void startStream() {
      // Check started again after we acquire the lock.
      if (!started) {
        delegate.start();
        started = true;
      }
    }
  
    @Override
    public void close() {
      delegate.shutdown();
    }
  
    Endpoint endpoint() {
      return endpoint;
    }
  }
  