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Apache Solr (module: core)
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/*
 * 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.solr.cluster.events.impl;

import com.google.common.annotations.VisibleForTesting;
import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.util.Set;
import java.util.concurrent.Phaser;
import org.apache.solr.cluster.events.ClusterEvent;
import org.apache.solr.cluster.events.ClusterEventListener;
import org.apache.solr.cluster.events.ClusterEventProducer;
import org.apache.solr.cluster.events.ClusterEventProducerBase;
import org.apache.solr.cluster.events.NoOpProducer;
import org.apache.solr.common.util.IOUtils;
import org.apache.solr.core.CoreContainer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This implementation allows Solr to dynamically change the underlying implementation of {@link
 * ClusterEventProducer} in response to the changed plugin configuration.
 */
public final class DelegatingClusterEventProducer extends ClusterEventProducerBase {
  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

  private ClusterEventProducer delegate;
  // support for tests to make sure the update is completed
  private volatile Phaser phaser;

  public DelegatingClusterEventProducer(CoreContainer cc) {
    super(cc);
    delegate = new NoOpProducer(cc);
  }

  @Override
  public void close() throws IOException {
    if (log.isDebugEnabled()) {
      log.debug("--closing delegate for CC-{}: {}", Integer.toHexString(cc.hashCode()), delegate);
    }
    IOUtils.closeQuietly(delegate);
    super.close();
  }

  /**
   * A phaser that will advance phases every time {@link #setDelegate(ClusterEventProducer)} is
   * called. Useful for allowing tests to know when a new delegate is finished getting set.
   */
  @VisibleForTesting
  public void setDelegationPhaser(Phaser phaser) {
    phaser.register();
    this.phaser = phaser;
  }

  public void setDelegate(ClusterEventProducer newDelegate) {
    if (log.isDebugEnabled()) {
      log.debug(
          "--setting new delegate for CC-{}: {}", Integer.toHexString(cc.hashCode()), newDelegate);
    }
    this.delegate = newDelegate;
    // transfer all listeners to the new delegate
    listeners.forEach(
        (type, listenerSet) -> {
          listenerSet.forEach(
              listener -> {
                try {
                  delegate.registerListener(listener, type);
                } catch (Exception e) {
                  log.warn("Exception registering listener with the new event producer", e);
                  // make sure it's not registered
                  delegate.unregisterListener(listener, type);
                  // unregister it here, too
                  super.unregisterListener(listener, type);
                }
              });
        });
    if ((state == State.RUNNING || state == State.STARTING)
        && !(delegate.getState() == State.RUNNING || delegate.getState() == State.STARTING)) {
      try {
        delegate.start();
        if (log.isDebugEnabled()) {
          log.debug("--- started delegate {}", delegate);
        }
      } catch (Exception e) {
        log.warn("Unable to start the new delegate {}: {}", delegate.getClass().getName(), e);
      }
    } else {
      if (log.isDebugEnabled()) {
        log.debug("--- delegate {} already in state {}", delegate, delegate.getState());
      }
    }
    Phaser localPhaser = phaser; // volatile read
    if (localPhaser != null) {
      assert localPhaser.getRegisteredParties() == 1;
      // we should be the only ones registered, so this will advance phase each time
      localPhaser.arrive();
    }
  }

  @Override
  public void registerListener(
      ClusterEventListener listener, ClusterEvent.EventType... eventTypes) {
    super.registerListener(listener, eventTypes);
    delegate.registerListener(listener, eventTypes);
  }

  @Override
  public void unregisterListener(
      ClusterEventListener listener, ClusterEvent.EventType... eventTypes) {
    super.unregisterListener(listener, eventTypes);
    delegate.unregisterListener(listener, eventTypes);
  }

  @Override
  public synchronized void start() throws Exception {
    if (log.isDebugEnabled()) {
      log.debug(
          "-- starting CC-{}, Delegating {}, delegate {}",
          Integer.toHexString(cc.hashCode()),
          Integer.toHexString(hashCode()),
          delegate);
    }
    state = State.STARTING;
    if (!(delegate.getState() == State.RUNNING || delegate.getState() == State.STARTING)) {
      try {
        delegate.start();
        if (log.isDebugEnabled()) {
          log.debug("--- started delegate {}", delegate);
        }
      } finally {
        state = delegate.getState();
      }
    } else {
      if (log.isDebugEnabled()) {
        log.debug("--- delegate {} already in state {}", delegate, delegate.getState());
      }
    }
  }

  @Override
  public Set getSupportedEventTypes() {
    return NoOpProducer.ALL_EVENT_TYPES;
  }

  @Override
  public synchronized void stop() {
    if (log.isDebugEnabled()) {
      log.debug(
          "-- stopping Delegating {}, delegate {}", Integer.toHexString(hashCode()), delegate);
    }
    state = State.STOPPING;
    delegate.stop();
    state = delegate.getState();
  }
}