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

Berwin A Turlach berwin at maths.uwa.edu.au
Fri Feb 20 18:52:13 CET 2009

G'day Brian,

On Fri, 20 Feb 2009 11:37:18 +0000 (GMT)
Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:

> This was rather a large shift of subject, [...] 

Well, yes, from the clean unloading of compiled code to the clean
unloading of R code.  :-)  
Though, I also confirmed that the former is possible on a cooperative
OS when library.dynam.unload() is correctly used via an .onUnload()

> Is lazy loading involved? 

Yes, the DESCRIPTION file has the default "LazyLoad: yes" entry. 

If I set "LazyLoad: no", then both sequences use the new version of the
R code immediately.

> 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.

As far as I can tell, "detach(foo, unload=TRUE)" and
"unloadNamespace(foo)" behave identical on my machines (while the
DESCRIPTION file has "LazyLoad: yes"); the modified R code is only used
if either of this command is given (followed by "library(foo)") after
the new version of the package was installed. 

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

Unfortunately, the former does not work and although the latter works I
am hesitant to use it since:

a) as I understand it, most packages that use S4 methods need
lazy-loading (though the particular package with which I noticed the
behaviour does not have S4 methods); and

b) it seems that these days the DESCRIPTION file is the only way of
switching lazy loading on and off and that there is no way of
overriding that value.  Knowing myself, I would forget changing the
DESCRIPTION file back to "LazyLoad: yes" before building the .tar.gz
file for distribution (once the package is ready).  As it is, I have
already to remember to take "-Wall -pedantic" out of the Makevars file
in the src/ directory; but I am reminded of that by R CMD check.

Well, thinking a bit more about b), I could probably complicate my
Makefile a bit more such that a "make install" first modifies the
DESCRIPTION file to "LazyLoad: no" before installing the package to the
local library and that "make build" first modifies the DESCRIPTION in
the opposite way.  But this would still leave concern a).



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