/**
    * 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<Procedure> runnables = new ArrayDeque<Procedure>();
    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) {
   }
 }