Linear closure accesses shared mutable variable of active object

[Dave Clarke]

It seems that a linear closure that accesses the mutable state of an active object can be passed outside of the active object, creating a potential race condition on the mutable state between the closure and the active object. The following example compiles (though it does not exhibit a race condition), when perhaps it shouldn't.

This problem occurs in the HEAD of development.

  def main() : unit
    val bar = new Bar(10)
    val f = get(bar!clo())
    println(f(12))
  end
end

active class Bar
  var foo : int
  def init(i : int) : unit
    this.foo = i
  end

  def clo() : linear ((int) -> int)
    fun (x : int) : int
      this.foo + x
    end
  end
end