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;
  
  import com.google.auto.service.AutoService;
  import java.io.Closeable;
  import java.util.ServiceLoader;
  import org.apache.beam.runners.core.metrics.ExecutionStateTracker;
  
  /**
   * A {@link ContextActivationObserver} provides a contract to register objects with the
   * DataflowExecutionContext.
   *
   * <p>All methods of a {@link ContextActivationObserver} are required to be thread safe.
   */
  public interface ContextActivationObserver extends Closeable {
    /**
     * Returns a {@link Closeable} based on the given {@link ExecutionStateTracker}. The closeable
     * will be invoked when the {@link DataflowExecutionContext} is deactivated.
     */
    public Closeable activate(ExecutionStateTracker executionStateTracker);
  
    /**
     * {@link ContextActivationObserver}s can be automatically registered with this SDK by creating a
     * {@link ServiceLoader} entry and a concrete implementation of this interface.
     *
     * <p>It is optional but recommended to use one of the many build time tools such as {@link
     * AutoService} to generate the necessary META-INF files automatically.
     */
    public interface Registrar {
      /**
       * Returns a boolean indicating whether DataflowExecutionContext should register this observer
       * or not.
       */
      boolean isEnabled();
  
      /**
       * Returns a {@link ContextActivationObserver} which will be registered by default within each
       * {@link ContextActivationObserverRegistry registry} instance.
       */
      ContextActivationObserver getContextActivationObserver();
    }
  }
  