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.calcite.util;
  
  import org.apache.calcite.plan.Context;
  import org.apache.calcite.plan.RelOptPlanner;
  
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * CancelFlag is used to post and check cancellation requests.
   *
   * <p>Pass it to {@link RelOptPlanner} by putting it into a {@link Context}.
   */
  public class CancelFlag {
    //~ Instance fields --------------------------------------------------------
  
    /** The flag that holds the cancel state.
     * Feel free to use the flag directly. */
    public final AtomicBoolean atomicBoolean;
  
    public CancelFlag(AtomicBoolean atomicBoolean) {
      this.atomicBoolean = requireNonNull(atomicBoolean, "atomicBoolean");
    }
  
    //~ Methods ----------------------------------------------------------------
  
    /** Returns whether a cancellation has been requested. */
    public boolean isCancelRequested() {
      return atomicBoolean.get();
    }
  
    /**
     * Requests a cancellation.
     */
    public void requestCancel() {
      atomicBoolean.compareAndSet(false, true);
    }
  
    /**
     * Clears any pending cancellation request.
     */
    public void clearCancel() {
      atomicBoolean.compareAndSet(true, false);
    }
  }
  