[Rd] Exiting R and package detachment?

Henrik Bengtsson hb at maths.lth.se
Fri Jun 10 13:55:16 CEST 2005

Prof Brian Ripley wrote:
> Note that you can terminate R via q() without running .Last, and indeed 
> how R is terminated is up to the front-end in use.  So the answer to
>> is there away to assure that a package is detached when R quits?
> is `No'.

Thank you for this. After rereading the ?Last, I wonder, is it 
.Internal(quit(...)) that calls .Last() or is it some other lower-level 
mechanism that does this?  In other words, is it only when 
quit(runLast=TRUE) is called that .Last() is called?


PS. I know the answer is in the source code, but I'm behind a 56k modem 
without having the source code on my laptop. DS.

> On Fri, 10 Jun 2005, Henrik Bengtsson wrote:
>> Hi,
>> is there away to assure that a package is detached when R quits?  I know
>> about .Last(), but that requires the user to setup that function.  What
>> I am looking for is a way for the package to do this itself, without
>> asking the user to edit "their" .Last().  From ?setHook I know that:
>>   "...when an R is finished, packages are not detached and namespaces
>> are not unloaded, so the corresponding hooks will not be run."
>> I am going to use this to load settings from file when a package loads
>> and automatically save (by optionally prompting the user) them back to
>> file when the package is no longer available (==detached/unloaded/R
>> quits).  I am currently loading the settings in .First.lib() and have
>> code in .Last.lib() to save them.
>> Are there other ways to assure functions to be called when R quits?  The
>> best I can think of now is to "hack" .Last() by doing something like
>> if (!exists(".LastOriginal", mode="function")) {
>>   .LastOriginal <<- get(".Last", envir=.GlobalEnv);
>>   .Last <<- function(..., envir=parent.frame()) {
>>     for (fun in getHook(".Last")) {
>>       if (is.character(fun))
>>         fun <- get(fun, mode="function")
>>       try(fun());
>>     }
>>     eval(.LastOriginal(...), envir=envir);
>>   } # .Last()
>> }
>> Then in package <pkg>:
>> .First.lib <- function(libname, pkgname) {
>>   # Detach package when R finishes.
>>   setHook(".Last", function(...) {
>>     pos <- match(paste("package:", pkgname, sep=""), search());
>>     if (!is.na(pos))
>>       detach(pos=pos);
>>   })
>> }
>> However, this will be broken if user redefines .Last().  What about
>> defining a hook "onSessionExit" to be called before (after?) .Last() is
>> called.  In analogue to on.exit() one could then define
>> onSessionExit <- function(fcn, ...) {
>>   setHook("onSessionExit", fcn, ...);
>> }
>> Just curious, the above quote makes me wonder what is the rational for
>> the behavior?  Was it made on purpose or is it simply just easier for R
>> to finish without detaching/unloading packages first?  In what
>> situations to you have "clean-up" code for a package that is only called
>> when detach("package:<pkg>") is used?  One situation I can imaging is
>> when a bundle of packages are loaded and when you detach the package
>> that all other packages requires, the other packages are also detached
>> for conveniency.
>> Best wishes
>> Henrik
>> ______________________________________________
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