/*
    * 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();
    }
  }