/**
 * Copyright 2008 Google Inc.
 *
 * Licensed 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.waveprotocol.wave.client.scheduler;

import com.google.gwt.user.client.Command;

/**
 * A command that will be notified if it isn't going to be execute()d.
 *
 */
public interface CancellableCommand extends Command {
  /**
   * A do-nothing instance.
   */
  public static final CancellableCommand NO_OP = new CancellableCommand() {
    @Override
    public void execute() {}

    @Override
    public void onCancelled() {}
  };

  /**
   * Indicate to this command that it will never be execute()d.
   */
  void onCancelled();
}