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Memory leak caused by scala.reflect.internal.util.Statistics #7130

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scabug opened this issue Feb 14, 2013 · 4 comments
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Memory leak caused by scala.reflect.internal.util.Statistics #7130

scabug opened this issue Feb 14, 2013 · 4 comments
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@scabug
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scabug commented Feb 14, 2013

In Types.scala we have the following code:

  Statistics.newView("#unique types") { if (uniques == null) 0 else uniques.size }

Let's have a closer look at Statistics.newView:

def newView(prefix: String, phases: String*)(quant: => Any): View = new View(prefix, phases, quant)

As you can see newView takes by-name argument (that in our case closes over the whole Global) and passes it to View.

The View class inherits from Quantity that is defined as follows:

  trait Quantity {
    if (prefix.nonEmpty) {
      val key = s"${if (underlying != this) underlying.prefix else ""}/$prefix"
      qs(key) = this
    }
    val prefix: String
    val phases: Seq[String]
    def underlying: Quantity = this
    def showAt(phase: String) = phases.isEmpty || (phases contains phase)
    def line = f"$prefix%-30s: ${this}"
    val children = new mutable.ListBuffer[Quantity]
  }

So we register this in global (defined in top-level object) HashMap stored in variable qs. The consequence is that even if you don't use Global it'll be still hanging there because Statistics holds reference to it. This is a memory leak that I observed while using Scala IDE where Global used for compiling the code was kept around and consumed aroung 0.5GB of heap.

@scabug
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scabug commented Feb 14, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7130?orig=1
Reporter: @gkossakowski
Affected Versions: 2.10.0, 2.10.1-RC1

@scabug
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scabug commented Feb 14, 2013

@gkossakowski said:
Added Iulian to watchers as he might be interested in this ticket.

@scabug
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scabug commented Feb 14, 2013

@gkossakowski said:
The simple solution to avoid memory leak is to turn all operations in Statistics into no-ops in case statistics is disabled.

However, the whole design is broken because it doesn't work across many Globals. Also, life cycle of that top-level object is not clear to me since you can mutate enabled flag at any time.

@scabug
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scabug commented Feb 19, 2013

@JamesIry said:
scala/scala#2129

@scabug scabug closed this as completed Feb 19, 2013
@scabug scabug added the critical label Apr 7, 2017
@scabug scabug added this to the 2.10.2-RC1 milestone Apr 7, 2017
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