measure/src/main/scala/org/apache/griffin/measure/context/streaming/metric/CacheResults.scala

/*
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regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
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  http://www.apache.org/licenses/LICENSE-2.0

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specific language governing permissions and limitations
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*/
package org.apache.griffin.measure.context.streaming.metric

import scala.collection.mutable.{Map => MutableMap}

import org.apache.griffin.measure.Loggable


/**
  * in streaming mode, some metrics may update,
  * the old metrics are cached here
  */
object CacheResults extends Loggable {

  case class CacheResult(timeStamp: Long, updateTime: Long, result: Metric) {
    def olderThan(ut: Long): Boolean = updateTime < ut
    def update(ut: Long, r: Metric): Option[Metric] = {
      r match {
        case m: result.T if (olderThan(ut)) =>
          val ur = result.update(m)
          if (result.differsFrom(ur)) Some(ur) else None
        case _ => None
      }
    }
  }

  private val cacheGroup: MutableMap[Long, CacheResult] = MutableMap()

  private def update(r: CacheResult): Unit = {
    cacheGroup += (r.timeStamp -> r)
  }

  /**
    * input new metric results, output the updated metric results.
    */
  def update(cacheResults: Iterable[CacheResult]): Iterable[CacheResult] = {
    val updatedCacheResults = cacheResults.flatMap { cacheResult =>
      val CacheResult(t, ut, r) = cacheResult
      (cacheGroup.get(t) match {
        case Some(cr) => cr.update(ut, r)
        case _ => Some(r)
      }).map(m => CacheResult(t, ut, m))
    }
    updatedCacheResults.foreach(r => update(r))
    updatedCacheResults
  }

  /**
    * clean the out-time cached results, to avoid memory leak
    */
  def refresh(overtime: Long): Unit = {
    val curCacheGroup = cacheGroup.toMap
    val deadCache = curCacheGroup.filter { pr =>
      val (_, cr) = pr
      cr.timeStamp < overtime || cr.result.eventual()
    }
    info(s"=== dead cache group count: ${deadCache.size} ===")
    deadCache.keySet.foreach(cacheGroup -= _)
  }

}