[Rd] Determining the exit code of an "almost finished" R script

Duncan Murdoch murdoch@dunc@n @end|ng |rom gm@||@com
Sat Jun 8 18:50:33 CEST 2019

On 08/06/2019 9:55 a.m., Gergely Daróczi wrote:
> On Sat, Jun 8, 2019 at 2:13 PM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>> On 08/06/2019 7:42 a.m., Gergely Daróczi wrote:
>>> Dear All,
>>> I'm using "reg.finalizer" in a function that is to be called in R scripts
>>> to do some cleanup on success. I have not found a way to run the function
>>> only if the script run without errors, so when the exit code is expected to
>>> be 0.
>>> What I've tried is checking "geterrmessage()", but unfortunately it's not
>>> perfect: if an error was handled with eg "tryCatch" previously, that
>>> message still shows up there.
>>> Is there any better way of figuring out in "reg.finalizer" or ".Last" if
>>> the session run OK or exiting with !0 exit code?
>> Can't you just put the line to run it as the last line of your script?
>> You won't get there if there was an error.
> Thank you very much, Duncan, but unfortunately, that's not feasible.
> "reg.finalizer" is called from a function early in the script, which
> function first checks when the same script last run and optionally
> exists early.

> If that optional early exit (within the helper function) doesn't
> happen, then the "reg.finalizer" call sets a status update when the R
> script has finished, but that should only happen if the script run
> without any problems.
> Of course, this helper could be split into two -- (1) function call at
> the beginning of the script and (2) another at the end, but it would
> be much less elegant and error-prone.
> I know I'm trying to hack-in some features in my R scripts that should
> be better handled by an external job scheduler, but I hope this is
> doable.

I still think you're using reg.finalizer() in a way it's not designed to 
work, and this makes it more complicated than necessary.  The strategy 
of splitting into two seems safer to me:  you never know when a 
finalizer will be called, because it is triggered by garbage 
collections, and those can happen asynchronously, not under your control.

It is nice to have all code for some purpose in one place, so if you 
really want that, you could put together your own explicitly called 
finalizer, something like this:

   finalizers <- list()

   addFinalizer <- function(fn) {
     finalizers <<- c(finalizers, list(fn))

   runFinalizers <- function() {
     for (i in rev(seq_along(finalizers))) { # Run in reverse order
       finalizers[[i]]()       # Call the finalizer
       finalizers[[i]] <- NULL # Allow related objects to be released

In the place you now call reg.finalizer(), you call addFinalizer() 
instead; so all code specific to that task remains local.  At the end of 
your script if things have been successful, you call runFinalizers().

Duncan Murdoch

>> The point of reg.finalizer is to run code even if there was an error;
>> your situation is much simpler.
>> Duncan Murdoch

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