From luke-tier@ey m@ili@g off uiow@@edu  Thu Aug  9 21:13:21 2018
From: luke-tier@ey m@ili@g off uiow@@edu (luke-tier@ey m@ili@g off uiow@@edu)
Date: Thu, 9 Aug 2018 14:13:21 -0500 (CDT)
Subject: [Rd] 
 SIGSEGV in R_RunWeakRefFinalizer, object allocated with Rcpp
In-Reply-To: <23404.36580.740017.811392@rob.eddelbuettel.com>
References: <CALEXWq2E+-k=Oka1YZAzGzYU1bLmcC3ptUUrv8RUMUrpcviK-g@mail.gmail.com>
 <a03f65c7-3e0e-7857-0e1e-a809e1051b56@gmail.com>
 <23404.36580.740017.811392@rob.eddelbuettel.com>
Message-ID: <alpine.DEB.2.20.1808091406240.3237@luke-Latitude-7480>

On Thu, 9 Aug 2018, Dirk Eddelbuettel wrote:

>
> On 9 August 2018 at 20:37, Tomas Kalibera wrote:
> | So to answer your original question, this could probably be handled in
> | Rcpp,
>
> Hm. Why do you say that / what did you have in mind?

We say it because it is true. Rcpp registers C finalizers and running
them after unloading will segfault. For now it would be better for Rcpp
(and everyone else) to explicitly discourage unloading as it is
unreliable on many levels.

What Rcpp could do to avoid segfaulting is to keep a weak list of all
objects to which it attaches C finalizers and arrange for those to be
cleaned up in an R_unload_<dllname> routine. Not clear it is worth the
trouble. At the R level we could provide more support for this since
we already have a weak list of objects with finalizers, but again not
clear it is worth the trouble.

Best,

luke

> Recall that we do not alter SEXPs or introduce additional additional
> reference counters -- because we do not think that altering the basic R API
> for such calls would be a wise strategy.  So we do more or less what is done
> in C for R, with some additional hand-holding which circumvents a number of
> common errors.
>
> | but in either case I would not use dyn.unload() in the first
> | place. This problem may be just one of many.
>
> I think I'd second that. I never had much unloading packages or dynamic
> libraries and tend to "just say no". Both short-lived processes (ie via 'r')
> as well as long sessions (ie R via ESS, running for weeks) work for my
> workflows.
>
> Dirk
>
>

-- 
Luke Tierney
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-tierney at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu



[Rd] SIGSEGV in R_RunWeakRefFinalizer, object allocated with Rcpp
luke-tier@ey m@ili@g off uiow@@edu