[Rd] [External] The finalizer of the externalPtr does not work when closing R?

[iuke-tier@ey m@iii@g oii uiow@@edu]

Use R_RegisterFinalizerEx in your C code. See

https://cran.r-project.org/doc/manuals/r-release/R-exts.html#External-pointers-and-weak-references

This still gives you only "best effort"; for anything stronger you
would need a different approach.

In general, finalizers should only be used as a backstop, not as a
primary resource management tool (in R or any other garbage-collected
language).

Memory leaks are not an issue -- unless you are doing very unusual
things your OS will reclaim memory resources used by your process when
it exits, cleanly or otherwise.

Best,

luke

On Fri, 3 Apr 2020, Wang Jiefei wrote:

> Hi all,
>
> I found that the finalizer of the externalPtr is not called when R is
> quitting. However, manually calling GC() works fine. This behavior is
> observed on devel R 2020-04-02 r78142 on Win and R 3.6.3 on Ubuntu.  I make
> a reproducible package here: https://github.com/Jiefei-Wang/example
>
> Here is the detail of how to reproduce the problem, I create a temporary
> file in the package root path and make an external pointer. The finalizer
> of the external pointer will delete the  temporary file when it is called.
> In the first round, I manually remove the external pointer from the global
> environment and call GC() to verify if the finalizer is programmed
> properly. The temporary file is deleted successfully. Then I create the
> file and the pointer again and close the R session without saving the
> global environment. Since the external pointer is removed when closing R,
> so the finalizer should be called in this procedure. However, the temp file
> still exists after closing the R session.
>
> Here is the test code(which can be found in inst/example/example.R)
>
> ## Create a temporary file
> tmpFile <- paste0(system.file(package = "testPackage"), "/tmp")
> tmpFile
> file.create(tmpFile)
> file.exists(tmpFile)
> ## Create an external pointer whose finalizer will delete
> ## the file when the variable is not in used
> x <- testPackage:::makeExtPtr(file.remove,tmpFile)
> ## GC is working fine
> rm(list="x")
> gc()
> file.exists(tmpFile)
>
> ## Create the temporary file again
> file.create(tmpFile)
> file.exists(tmpFile)
> x <- testPackage:::makeExtPtr(file.remove,tmpFile)
> ## Quit R session without explicitly cleaning the working space
> quit(save = "no")
>
>
> ##=====Open a new R session=======
> ## The temporary file still exist
> tmpFile <- paste0(system.file(package = "testPackage"), "/tmp")
> file.exists(tmpFile)
>
> Not sure if this behavior is designed on purpose, but it sounds wired to me
> and can cause memory leaking if not properly handled.
>
> Best,
> Jiefei
>
> 	[[alternative HTML version deleted]]
>
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-- 
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
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