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/**
 * 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.hadoop.hbase.procedure2;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;

/**
 * Simple runqueue for the procedures
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class ProcedureSimpleRunQueue implements ProcedureRunnableSet {
  private final Deque runnables = new ArrayDeque();
  private final ReentrantLock lock = new ReentrantLock();
  private final Condition waitCond = lock.newCondition();

  @Override
  public void addFront(final Procedure proc) {
    lock.lock();
    try {
      runnables.addFirst(proc);
      waitCond.signal();
    } finally {
      lock.unlock();
    }
  }

  @Override
  public void addBack(final Procedure proc) {
    lock.lock();
    try {
      runnables.addLast(proc);
      waitCond.signal();
    } finally {
      lock.unlock();
    }
  }

  @Override
  public void yield(final Procedure proc) {
    addBack(proc);
  }

  @Override
  @edu.umd.cs.findbugs.annotations.SuppressWarnings("WA_AWAIT_NOT_IN_LOOP")
  public Procedure poll() {
    lock.lock();
    try {
      if (runnables.isEmpty()) {
        waitCond.await();
        if (!runnables.isEmpty()) {
          return runnables.pop();
        }
      } else {
        return runnables.pop();
      }
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      return null;
    } finally {
      lock.unlock();
    }
    return null;
  }

  @Override
  public void signalAll() {
    lock.lock();
    try {
      waitCond.signalAll();
    } finally {
      lock.unlock();
    }
  }

  @Override
  public void clear() {
    lock.lock();
    try {
      runnables.clear();
    } finally {
      lock.unlock();
    }
  }

  @Override
  public int size() {
    lock.lock();
    try {
      return runnables.size();
    } finally {
      lock.unlock();
    }
  }

  @Override
  public void completionCleanup(Procedure proc) {
  }
}