measure/src/main/scala/org/apache/griffin/measure/datasource/cache/WithFanIn.scala

/*
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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

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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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specific language governing permissions and limitations
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*/
package org.apache.griffin.measure.datasource.cache

import java.util.concurrent.atomic.AtomicInteger

import scala.collection.concurrent.{Map => ConcMap, TrieMap}

/**
  * fan in trait, for multiple input and one output
  * to support multiple parallel data connectors in one data source
  */
trait WithFanIn[T] {

  // total input number
  val totalNum: AtomicInteger = new AtomicInteger(0)
  // concurrent map of fan in count for each key
  val fanInCountMap: ConcMap[T, Int] = TrieMap[T, Int]()

  def registerFanIn(): Int = {
    totalNum.incrementAndGet()
  }

  /**
    * increment for a key, to test if all parallel inputs finished
    * @param key
    * @return
    */
  def fanIncrement(key: T): Boolean = {
    fanInc(key)
    fanInCountMap.get(key) match {
      case Some(n) if (n >= totalNum.get) => {
        fanInCountMap.remove(key)
        true
      }
      case _ => false
    }
  }

  private def fanInc(key: T): Unit = {
    fanInCountMap.get(key) match {
      case Some(n) =>
        val suc = fanInCountMap.replace(key, n, n + 1)
        if (!suc) fanInc(key)
      case _ =>
        val oldOpt = fanInCountMap.putIfAbsent(key, 1)
        if (oldOpt.nonEmpty) fanInc(key)
    }
  }

}