Lifetime of a local reference

Alan Bawden alan at csail.mit.edu
Thu Feb 28 02:04:42 EST 2019


Gregory Ewing <greg.ewing at canterbury.ac.nz> writes:

> Alan Bawden wrote:
> > the Java Language
> > Specification contains the following language:
> >    Optimizing transformations of a program can be designed that reduce
> >    the number of objects that are reachable to be less than those which
> >    would naively be considered reachable.  For example, a Java compiler
> >    or code generator may choose to set a variable or parameter that
> >    will no longer be used to null to cause the storage for such an
> >    object to be potentially reclaimable sooner.
> 
> However, it only makes sense to do that if the compiler can be
> sure that reclaiming the object can't possibly have any side
> effects. That's certainly not true of things like file objects
> that reference resources outside of the program. I'd be pretty
> upset if a Java implementation prematurely closed my files on
> the basis of this clause.

The Java compiler has no way to know whether a variable references an
object with a finalize() method that has side effects, so that quote from
the Specification licenses a Java implementation to do exactly the thing
you say will make you upset.

-- 
Alan Bawden


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