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 edu.umd.cs.findbugs.annotations.NonNull;
  import io.netty.util.concurrent.FastThreadLocalThread;
  import java.util.concurrent.ThreadFactory;
  
  /**
   * Safeguards against bad usage patterns in client code that could introduce deadlocks in the
   * driver.
   *
   * <p>The driver internals are fully asynchronous, nothing should ever block. On the other hand, our
   * API exposes synchronous wrappers, that call async methods and wait on the result (as a
   * convenience for clients that don't want to do async). These methods should never be called on a
   * driver thread, because this can lead to deadlocks. This can happen from client code if it uses
   * callbacks.
   */
  public class BlockingOperation {
  
    /**
     * This method is invoked from each synchronous driver method, and checks that we are not on a
     * driver thread.
     *
     * <p>For this to work, all driver threads must be created by {@link SafeThreadFactory} (which is
     * the case by default).
     *
     * @throws IllegalStateException if a driver thread is executing this.
     */
    public static void checkNotDriverThread() {
      if (Thread.currentThread() instanceof InternalThread) {
        throw new IllegalStateException(
            "Detected a synchronous API call on a driver thread, "
                + "failing because this can cause deadlocks.");
      }
    }
  
    /**
     * Marks threads as driver threads, so that they will be detected by {@link
     * #checkNotDriverThread()}
     */
    public static class SafeThreadFactory implements ThreadFactory {
      @Override
      public Thread newThread(@NonNull Runnable r) {
        return new InternalThread(r);
      }
    }
  
    static class InternalThread extends FastThreadLocalThread {
      private InternalThread(Runnable runnable) {
        super(runnable);
      }
    }
  }
  