/*

  * 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.giraph.comm.netty.handler;

 import com.google.common.collect.Maps;

 import java.util.concurrent.ConcurrentMap;

 import java.util.concurrent.atomic.AtomicLong;

 /**

  * Generate different request ids based on the task id.  Thread-safe.

  */

 public class TaskRequestIdGenerator {

   /** Task request generator map */

   private final ConcurrentMap<Integer, AtomicLong>

       taskRequestGeneratorMap = Maps.newConcurrentMap();

   /**

    * Get the next request id for a given destination.  Thread-safe.

    *

    * @param taskId id of the task(consistent during a superstep)

    * @return Valid request id

    */

   public Long getNextRequestId(Integer taskId) {

     AtomicLong requestGenerator = taskRequestGeneratorMap.get(taskId);

     if (requestGenerator == null) {

       requestGenerator = new AtomicLong(0);

       AtomicLong oldRequestGenerator =

           taskRequestGeneratorMap.putIfAbsent(taskId, requestGenerator);

       if (oldRequestGenerator != null) {

         requestGenerator = oldRequestGenerator;

       }

     }

     return requestGenerator.getAndIncrement();

   }

 }