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 com.datastax.oss.driver.internal.core.util.concurrent;
  
  import com.datastax.oss.driver.shaded.guava.common.annotations.VisibleForTesting;
  import com.datastax.oss.driver.shaded.guava.common.graph.Graphs;
  import com.datastax.oss.driver.shaded.guava.common.graph.MutableValueGraph;
  import com.datastax.oss.driver.shaded.guava.common.graph.ValueGraphBuilder;
  import net.jcip.annotations.ThreadSafe;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /** Detects cycles between a set of {@link LazyReference} instances. */
  @ThreadSafe
  public class CycleDetector {
    private static final boolean ENABLED =
        Boolean.getBoolean("com.datastax.oss.driver.DETECT_CYCLES");
    private static final Logger LOG = LoggerFactory.getLogger(CycleDetector.class);
  
    private final String errorMessage;
    private final boolean enabled;
    private final MutableValueGraph<String, String> graph;
  
    public CycleDetector(String errorMessage) {
      this(errorMessage, ENABLED);
    }
  
    @VisibleForTesting
    CycleDetector(String errorMessage, boolean enabled) {
      this.errorMessage = errorMessage;
      this.enabled = enabled;
      this.graph = enabled ? ValueGraphBuilder.directed().build() : null;
    }
  
    void onTryLock(LazyReference<?> reference) {
      if (enabled) {
        synchronized (this) {
          Thread me = Thread.currentThread();
          LOG.debug("{} wants to initialize {}", me, reference.getName());
          graph.putEdgeValue(me.getName(), reference.getName(), "wants to initialize");
          LOG.debug("{}", graph);
          if (Graphs.hasCycle(graph.asGraph())) {
            throw new IllegalStateException(errorMessage + " " + graph);
          }
        }
      }
    }
  
    void onLockAcquired(LazyReference<?> reference) {
      if (enabled) {
        synchronized (this) {
          Thread me = Thread.currentThread();
          LOG.debug("{} is initializing {}", me, reference.getName());
          String old = graph.removeEdge(me.getName(), reference.getName());
          assert "wants to initialize".equals(old);
          graph.putEdgeValue(reference.getName(), me.getName(), "is getting initialized by");
        }
      }
    }
  
    void onReleaseLock(LazyReference<?> reference) {
      if (enabled) {
        synchronized (this) {
          Thread me = Thread.currentThread();
          LOG.debug("{} is done initializing {}", me, reference.getName());
          graph.removeEdge(reference.getName(), me.getName());
        }
      }
    }
  }
  