[External] make running on.exit expr uninterruptible

Hi,

Is there currently any way to guarantee that on.exit does not fail to execute the recorded expression because of a user interrupt arriving during function exit? Consider:

f <- function() {
 suspendInterrupts({
   on.exit(suspendInterrupts(cntr_on.exit <<- cntr_on.exit + 1L))
   cntr_f <<- cntr_f + 1L
 })
 TRUE
}

It is possible to interrupt this function such that cntr_f is incremented while cntr_on.exit is not (you might need to adjust timeout_upper to trigger the error on your machine):

timeout_upper <- 0.00001
repeat {
 cntr_f <- 0L
 cntr_on.exit <- 0L

 # timeout code borrowed from R.utils::withTimeout but with setTimeLimit()
 # (correctly) place inside tryCatch (otherwise timeout can occur before it can
 # be caught) and with time limit reset before going into the error handler
 res_list <- lapply(seq(0, timeout_upper, length.out = 1000), function(timeout) {
   on.exit({
     setTimeLimit(cpu = Inf, elapsed = Inf, transient = FALSE)
   })
   tryCatch({
     setTimeLimit(cpu = timeout, elapsed = timeout, transient = TRUE)
     res <- f()

     # avoid timeout while running error handler
     setTimeLimit(cpu = Inf, elapsed = Inf, transient = FALSE)

     res
   }, error = function(ex) {
     msg <- ex$message
     pattern <- gettext("reached elapsed time limit", "reached CPU time limit",
                        domain = "R")
     pattern <- paste(pattern, collapse = "|")
     if (regexpr(pattern, msg) != -1L) {
       FALSE
     }
     else {
       stop(ex)
     }
   })
 })
 print(sum(unlist(res_list)))  # number of times f completed
 stopifnot(cntr_on.exit == cntr_f)
}

Example output:

1] 1000
[1] 1000
[1] 1000
[1] 1000
[1] 999
[1] 1000
[1] 1000
[1] 999
[1] 998
[1] 1000
[1] 998
[1] 1000
[1] 1000
[1] 1000
[1] 1000
[1] 999
Error: cntr_on.exit == cntr_f is not TRUE

I was bitten by this because an on.exit expression, which releases a file lock, was interrupted (before it actually executed) such that subsequent calls block indefinitely.

Regards,
Andreas