FlatMapGC.scala

package com.normation

import scala.concurrent.Future
object CheckMemoryReleaseFlatMap {


  def getFreeMem = (Runtime.getRuntime().freeMemory() / (1024*1024)).toString + " MB"
  def doGC = {
    System.gc()
    System.runFinalization()
  }

  // this array is 200MB
  def newBigArray() = Array.fill(50 * 1024)(Array.fill(1024)("x"))

  implicit val ec = scala.concurrent.ExecutionContext.global

  /*
   * Configuring jvm with -Xmx500M -Xms500M
   */

  def test0(): Unit = {
    Future {
      doGC
      println("t0: " + getFreeMem)                   // t0: 493 MB
      doGC
      for {
        a <- Some(newBigArray())
        _ = doGC
        _ =  println("t1: " + getFreeMem)            // t1: 292 MB
        _ = doGC
        b <- Some(newBigArray())
        _ = doGC
        _ =  println("t2: " + getFreeMem)            // t2:  91 MB
        _ = doGC
      } yield {
        doGC
        Thread.sleep(2000)
        println("t3: " + getFreeMem)                 // t3:  91 MB
        Unit
      }
    }

    Thread.sleep(5000)
    doGC
    println("t4: " + getFreeMem)                     // t4: 493 MB

  }

  def test1(): Unit = {
    Future {
      doGC
      println("t0: " + getFreeMem)                   // t4: 493 MB
      doGC
      for {
        x <- for {
                a <- Some(newBigArray())
                _ = doGC
                _ =  println("t1: " + getFreeMem)    // t1: 292 MB
                _ = doGC
                b <- Some(newBigArray())
             } yield b
        _ = doGC
        _ =  println("t2: " + getFreeMem)            // t2: 292 MB
        _ = doGC
      } yield {
        doGC
        Thread.sleep(2000)
        println("t3: " + getFreeMem)                 // t3: 292 MB
        Unit
      }
    }

    Thread.sleep(5000)
    doGC
    println("t4: " + getFreeMem)                     // t4: 493 MB
  }

  def test2(): Unit = {
    doGC
    println("t0: " + getFreeMem)                     // t0: 493 MB
    doGC
    val a = Some(newBigArray())
    doGC
    println("t1: " + getFreeMem)                     // t1: 292 MB
    doGC
    val b = Some(newBigArray())
    doGC
    println("t2: " + getFreeMem)                     // t2:  91 MB
  }

  def test3(): Unit = {
    doGC
    println("t0: " + getFreeMem)                     // t0: 493 MB
    doGC

    {
      val a = Some(newBigArray())
      doGC
      println("t1: " + getFreeMem)                   // t1: 292 MB
      doGC
      val b = Some(newBigArray())
      doGC
      println("t2: " + getFreeMem)                   // t2:  91 MB
    }
    doGC
    println("t3: " + getFreeMem)                     // t3:  91 MB  => ????
  }

  def main(args: Array[String]): Unit = {
    println("======= test 0 ========")
    test0
    doGC
    println("======= test 1 ========")
    test1
    doGC
    println("======= test 2 ========")
    test2
    doGC
    println("======= test 3 ========")
    test3
  }
}