R devel - Jul 2011 - reg.finalizer and connection gc -- which runs when (and why)?

With this set-up

options(warn = 1)
tf <- tempfile()
finalizer <- function(obj) {
     message("finalizer")
     close(obj$f)
}

this code works

ev <- new.env()
ev$f <- file(tf, "w")
reg.finalizer(ev, finalizer)
rm(ev)
gc()

whereas this (reversing the order of file() and reg.finalizer())

ev <- new.env()
reg.finalizer(ev, finalizer)
ev$f <- file(tf, "w")
rm(ev)

produces

 > gc()
Warning: closing unused connection 3 (/tmp/Rtmp9CWLtN/file6998ee7b)
finalizer
Error in close.connection(obj$f) : invalid connection

In some respects, it seems like the user should get a chance to clean up 
their mess before the system does it for them, so the above seems like a 
bug. But maybe there is another way to understand this?

Martin
-- 
Computational Biology
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109

Location: M1-B861
Telephone: 206 667-2793

Connections use finalizers for cleanup.  Once finalizers become
eligible to run, the order in which they are run is unspecified.  If
you want to be sure yours runs first then you need to make sure the
connection one doesn't become eligible to run until yours has.

Best,

luke

On Thu, 21 Jul 2011, Martin Morgan wrote:
> With this set-up
>
> options(warn = 1)
> tf <- tempfile()
> finalizer <- function(obj) {
>    message("finalizer")
>    close(obj$f)
> }
>
> this code works
>
> ev <- new.env()
> ev$f <- file(tf, "w")
> reg.finalizer(ev, finalizer)
> rm(ev)
> gc()
>
> whereas this (reversing the order of file() and reg.finalizer())
>
> ev <- new.env()
> reg.finalizer(ev, finalizer)
> ev$f <- file(tf, "w")
> rm(ev)
>
> produces
>
>> gc()
> Warning: closing unused connection 3 (/tmp/Rtmp9CWLtN/file6998ee7b)
> finalizer
> Error in close.connection(obj$f) : invalid connection
>
> In some respects, it seems like the user should get a chance to clean up 
> their mess before the system does it for them, so the above seems like a
bug.
> But maybe there is another way to understand this?
>
> Martin
>
-- 
Luke Tierney
Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu