core/src/main/java/org/apache/calcite/util/CancelFlag.java

/*
 * 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.Objects;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * 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 = Objects.requireNonNull(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);
  }
}