generated java field in object left referencing stale data

[scabug]

Hi folks,

I'm working with latest the Scala repository and observe a Java instance field i n the compiler generated output that I presume does not belong. Worse, at runtime via Java reflection I access the field and find its referencing a java/scala object that to my thinking should be available to GC. So, I view this as a compiler generated code caused memory leak. the version of scala is

/common/bord/scala/scala/build/quick/bin/scala -version Scala code runner version 2.7.1.r14632-b20080411163142 -- (c) 2002-2008 LAMP/EPFL

and I'm using Java 6/Solaris 10 and/or Java 5/AIX for the test I also observed the same with 2.7.0GA where I first saw it. I include the code below and when run observe: ad.big$$1 is [I@e140e14

Note that if you change the code to comment out the (0 to 0).map ... line and use instead the new ... ArrayBuffer() ... line then the code up until the Console.println does the same thing, yet no big$$1 field is in A$$Helper$$2$$ and thus no memory issue and when run yields expected: Exception in thread "main" java.lang.NoSuchFieldException: big$$1

After the code listing is the javap -private output of the various .class files generated and one sees the A$$Helper$$2$$ having the big$$1 field

in my real world application "big" is a large intialization object constructed from parsing lots of data from a file and I want to see it getting GC'ed after its use in building the next stage object

Craig Bordelon bord@iscp.telcordia.com

object A { 
  abstract class DuringApply {
    val msg1:String 
    val msgs:RandomAccessSeq[String] 
  }

  def apply(n:int,z:int) = {
    val big = Array.make(n, z)

    object Helper extends DuringApply {
      val msg1 = big(0).toString 
      val msgs:RandomAccessSeq[String] =
        (0 to 0).map(big(_).toString) 
      //new scala.collection.mutable.ArrayBuffer?() ++ List(big(0).toString)
    }

    new AA(Helper)

  } 
  def main(args:Array[String]) {
    var a = A(1,1) 
    Console.println("ad.big$$1 is "+
     Class.forName("A$$Helper$$2$$").getDeclaredField("big$$1").get(a.ad))
  } 
}

class AA(val ad:A.DuringApply)

Compiled from "A.scala"
public final class A extends java.lang.Object{
    public static final int $$tag();
    public static final void main(java.lang.String[]);
    public static final AA apply(int, int);
}

Compiled from "A.scala"
public final class A$$ extends java.lang.Object implements scala.ScalaObject{
    public static final A$$ MODULE$$;
    public static {};
    public A$$();
    private final A$$Helper$$2$$ Helper$$1(int[], scala.runtime.ObjectRef);
    public void main(java.lang.String[]);
    public AA apply(int, int);
    public int $$tag();
}

Compiled from "A.scala"
public final class A$$Helper$$2$$ extends A$$DuringApply implements scala.ScalaObjec
t{
    public final int[] big$$1;
    private final scala.RandomAccessSeq msgs;
    private final java.lang.String msg1;
    public A$$Helper$$2$$(int[]);
    public scala.RandomAccessSeq msgs();
    public java.lang.String msg1();
}

Compiled from "A.scala"
public final class A$$Helper$$2$$$$anonfun$$1 extends java.lang.Object implements sca
la.Function1,scala.ScalaObject,java.io.Serializable{
    public final A$$Helper$$2$$ $$outer;
    public A$$Helper$$2$$$$anonfun$$1(A$$Helper$$2$$);
    public final java.lang.Object apply(java.lang.Object);
    public A$$Helper$$2$$ A$$Helper$$$$anonfun$$$$$$outer();
    public final java.lang.String apply(int);
    public int $$tag();
    public scala.Function1 andThen(scala.Function1);
    public scala.Function1 compose(scala.Function1);
    public java.lang.String toString();
}

Compiled from "A.scala"
public abstract class A$$DuringApply extends java.lang.Object implements scala.Sc
alaObject{
    public A$$DuringApply();
    public abstract scala.RandomAccessSeq msgs();
    public abstract java.lang.String msg1();
    public int $$tag();
}

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-743?orig=1 Reporter: cbordelo Attachments:

• A.scala (created on Apr 14, 2008 12:15:49 AM UTC, 3800 bytes)

[scabug]

cbordelo said: i also attach the file

[scabug]

@dragos said: You are right, there is indeed a problem. Let me first explain what happens: the big field is 'in scope' inside object Helper and as such, the most general case is handled by copying it into a field, when Helper is created. When such objects are used only during initialization, they should not get a field, and here it seems we could do better with a more sophisticated analysis. It seems the case you commented out is handled, so as a temporary solution you could go that way.

It might help to make the dependency explicit, by having an init method that takes the big object as parameter (and do so whenever big is needed). That way, the compiler will not see big as free, and won't generate these fields.

[scabug]

@dragos said: Well, I'm not so sure there is an easy fix for this issue...

[scabug]

@odersky said: It's indeed not so simple. We need to solve it, but can't do it right now.

[SethTisue]

Someone could look into whether the situation is any different or better in Scala 3.

[som-snytt]

By coincidence, I recently looked at it. Did the algorithm suggest this to you? Of all the gin joints etc.

IIRC S3 is no field, S2 is status quo. I haven't created a branch yet or assigned myself, as it seemed less like low-hanging and more like fruit on the ground, where it will not even bop anyone on the head like Newton's apple.