reg.finalizer() in an R package does not execute at the end of an R session

Question

From the documentation ?reg.finalizer in R:

Inter alia, it provides a way to program code to be run at the end of an R session without manipulating .Last. For use in a package, it is often a good idea to set a finalizer on an object in the namespace: then it will be called at the end of the session, or soon after the namespace is unloaded if that is done during the session.

It seems that I can use reg.finalizer() to run certain code when an R session is ended, but it does not work for me. I have prepared a minimal package at https://github.com/yihui/finalizer-test, which basically contains the code below:

e = new.env()

reg.finalizer(e, function(e) {
  message('Bye!')
}, onexit = TRUE)

If I simply run the above code in an interactive R session and quit the session, I can see the message Bye!, but if I install the above package (you can use devtools::install_github('yihui/finalizer-test')), load it in an R session, and quit the R session, I don't see the message. I wonder why the finalizer is not executed in this case.

FWIW, when I install the package, I can see the message Bye!:

$ R CMD INSTALL .

* installing to library ‘/Users/yihui/R’
* installing *source* package ‘finalizer’ ...
** R
** preparing package for lazy loading
No man pages found in package  ‘finalizer’ 
** help
*** installing help indices
Bye!
** building package indices
** testing if installed package can be loaded
* DONE (finalizer)

I don't see the message, either, when I run the command below:

$ R -e "library(finalizer)"
> library(finalizer)
> 
> 
$ 

Answer 1

It works if you register the finalizer function to the package name space environment. You can use the .onLoad hook for that:

e = new.env()

reg.finalizer(e, function(e) {
  message('Object Bye!')
}, onexit = TRUE)


finalize <- function(env) {
   print(ls(env))
   message("Bye from Name space Finalizer")
}


.onLoad <- function(libname, pkgname) {
   parent <- parent.env(environment())
   print(str(parent))
   reg.finalizer(parent, finalize, onexit= TRUE)
}

The object finalizer function is not called but since you have the whole namespace environment you probably don't need it.

I created a fork of your test package on https://github.com/mpbastos/finalizer-test:

> devtools::install_git("https://github.com/mpbastos/finalizer-test")
Downloading git repo https://github.com/mpbastos/finalizer-test
Installing finalizer
"C:/PROGRA~1/R/R-34~1.0/bin/x64/R" --no-site-file --no-environ --no-save  \
  --no-restore --quiet CMD INSTALL  \
  "C:/Users/mbastos/AppData/Local/Temp/RtmpOGymjQ/file5cf829e63957"  \
  --library="\\sharedfs/MyDocs6/mbastos/Documents/R/win-library/3.4"  \
  --install-tests

* installing *source* package 'finalizer' ...
** R
** preparing package for lazy loading
** help
No man pages found in package  'finalizer'
*** installing help indices
** building package indices
Object Bye!
** testing if installed package can be loaded
*** arch - i386
<environment: namespace:finalizer>
NULL
[1] "e"        "finalize"
Bye from Name space Finalizer
*** arch - x64
<environment: namespace:finalizer>
NULL
[1] "e"        "finalize"
Bye from Name space Finalizer
* DONE (finalizer)
> library(finalizer)
<environment: namespace:finalizer>
NULL
> q()
Save workspace image? [y/n/c]: n
[1] "e"        "finalize"
Bye from Name space Finalizer