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 java.util.ArrayList;
  import java.util.List;
  import java.util.ServiceLoader;
  import java.util.Set;
  import org.apache.beam.sdk.util.common.ReflectHelpers;
  import org.apache.beam.sdk.util.common.ReflectHelpers.ObjectsClassComparator;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Lists;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Sets;
  import org.slf4j.LoggerFactory;
  
  /**
   * A {@link ContextActivationObserverRegistry} allows creating a {@link ContextActivationObserver}.
   */
  public class ContextActivationObserverRegistry {
  
    static {
      LoggerFactory.getLogger(ContextActivationObserverRegistry.class);
    }
  
    private static final List<ContextActivationObserver>
        REGISTERED_CONTEXT_ACTIVATION_OBSERVER_FACTORIES;
  
    static {
      List<ContextActivationObserver> contextActivationObserversToRegister = new ArrayList<>();
  
      // Enumerate all the ContextActivationObserver.Registrars, adding them to registry.
      Set<ContextActivationObserver.Registrar> registrars =
          Sets.newTreeSet(ObjectsClassComparator.INSTANCE);
      registrars.addAll(
          Lists.newArrayList(
              ServiceLoader.load(
                  ContextActivationObserver.Registrar.class, ReflectHelpers.findClassLoader())));
  
      for (ContextActivationObserver.Registrar registrar : registrars) {
        if (registrar.isEnabled()) {
          contextActivationObserversToRegister.add(registrar.getContextActivationObserver());
        }
      }
  
      REGISTERED_CONTEXT_ACTIVATION_OBSERVER_FACTORIES =
          ImmutableList.copyOf(contextActivationObserversToRegister);
    }
  
    /**
     * Creates a ContextActivationObserverRegistry containing registrations for all standard
     * ContextActivationObservers part of the core Java Apache Beam SDK and also any registrations
     * provided by {@link ContextActivationObserver.Registrar}s.
     */
    public static ContextActivationObserverRegistry createDefault() {
      return new ContextActivationObserverRegistry();
    }
  
    /** The list of {@link ContextActivationObserver}s. */
    private final List<ContextActivationObserver> contextActivationObservers;
  
    private ContextActivationObserverRegistry() {
      contextActivationObservers = new ArrayList<>(REGISTERED_CONTEXT_ACTIVATION_OBSERVER_FACTORIES);
    }
  
    /** Returns all {@link ContextActivationObserver}s registered with this registry. */
    public List<ContextActivationObserver> getContextActivationObservers() {
      return contextActivationObservers;
    }
  }
  