[Rd] unloadNamespace (Was: How to unload a dll loaded via library.dynam()?)

Prof Brian Ripley ripley at stats.ox.ac.uk
Fri Feb 20 12:37:18 CET 2009

This was rather a large shift of subject, so I've pruned the 
recipients list.

Is lazy loading involved?  If so I have an idea that may or may not be 
relevant.  We do cache in memory the lazy-loading database for speed 
on slow (network-mounted or USB drive) file systems.  Now the cache is 
flushed at least if you do detach(foo, unload = TRUE) or but I can 
envisage a set of circumstances in which it might not be.

So perhaps try detach(foo, unload = TRUE) or not using lazy-loading 
when developing the package?

On Fri, 20 Feb 2009, Berwin A Turlach wrote:

> G'day all,
> On Fri, 20 Feb 2009 04:01:07 +0000 (GMT)
> Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
>> library.dynam.unload() does work if the OS is cooperative.  And if
>> you have your package set up correctly and unload the namespace (and
>> not just detach the package if there is a namespace) then the shared
>> object/DLL will be unloaded. [...]
> I guess I have a similar code-install-test development cycle as Alex;
> and I seem to work on a cooperative OS (Kubuntu 8.04).
> My set up is that I install packages on which I work into a separate
> library.  To test changes to such packages, I start R in a directory
> which contains a .Rprofile file which, via .libPaths(), adds the above
> library to the library path.  In this R session I then test the changes.
> I also used to quit and restart R whenever I re-installed a package with
> namespace to test the changes made.  Somehow I got the impression that
> this was the way to proceed when namespaces were introduced; and I did
> not realise until recently that better ways (unloading the namespace)
> exist.
> However, I noticed the following behaviour under R 2.8.1 and "R version
> 2.9.0 Under development (unstable) (2009-02-19 r47958)" which I found
> surprising:
> 1) In the running R session, issue the command "unloadNamespace(XXX)"
> 2) Do changes to the code of the package; e.g. add a "print("hello
>   world")" statement to one of the R functions.
> 3) Install the new package
> 4) In the running R session, issue the command "library(XXX)" and call
>   the R function that was changed.
> Result: "Hello world" is not printed, somehow the old R function is
> still used.  If I issue the commands "unloadNamespace(XXX)" and
> "library(XXX)" once more then a call to the R function that was changed
> will print "Hello world"; i.e. the new code is used.
> If the above sequence is changed to 2), 3) and then 1), then 4) behaves
> "as expected" and the new R code is used immediately.
> As far as I can tell, if via the .onUnload() hook the shared object is
> unloaded via library.dynam.unload(), changes in the C code take effect
> no matter whether I perform the above steps in the sequence 1-2-3-4 or
> 2-3-1-4.
> My preference is to use the sequence 1-2-3-4 since it seems to be the
> "more logical and cleaner" sequence; and I have vague memories that I
> managed to crash R in the past after using 2-3 and then trying to quit
> R.
> I am wondering why does it make a difference with respect to R code in
> which order these steps are done but not with respect to compiled
> code.  Well, I guess I understand why the order does not matter for
> compiled code, but I do not understand why the order matters for R
> code.  I could not find anything in the documentation that would
> explain this behaviour, or indicate that this is the intended
> behaviour.
> Enlightening comments and/or pointers to where this behaviour is
> documented would be welcome.
> Cheers,
> 	Berwin
> =========================== Full address =============================
> Berwin A Turlach                            Tel.: +65 6516 4416 (secr)
> Dept of Statistics and Applied Probability        +65 6516 6650 (self)
> Faculty of Science                          FAX : +65 6872 3919
> National University of Singapore
> 6 Science Drive 2, Blk S16, Level 7          e-mail: statba at nus.edu.sg
> Singapore 117546                    http://www.stat.nus.edu.sg/~statba

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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