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/**
 * Copyright (C) 2015 Red Hat, 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 io.fabric8.kubernetes.client.utils;

import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.Executor;

/**
 * See {@link Executor} docs
 * 
 * 
Effectively creates a derived single thread executor
 */
public class SerialExecutor implements Executor {
  final Queue tasks = new ArrayDeque<>();
  final Executor executor;
  Runnable active;

  public SerialExecutor(Executor executor) {
    this.executor = executor;
  }

  public synchronized void execute(final Runnable r) {
    tasks.offer(() -> {
      try {
        r.run();
      } finally {
        scheduleNext();
      }
    });
    if (active == null) {
      scheduleNext();
    }
  }

  protected synchronized void scheduleNext() {
    if ((active = tasks.poll()) != null) {
      executor.execute(active);
    }
  }
}