Functions not executing before Sys.sleep()

Question

I am writing a function that needs to catch a rate-limiting error while pinging a web-based API.

I am using tryCatch to catch the error, and inside this function I specify the following error function:

error=function(e) {
                warning(paste(e,"\nWaiting an hour for rate limit to reset..."))
                Sys.sleep(3600) # Wait an hour for rate-limit to reset
                return(user.info(user, ego.count))
            }

The function appears to work, but when checking the output logs for the script I notice that the warning message is not written until after the sleep time has run out.

I can reproduce this behavior at the R console with:

print("Drew sucks")
Sys.sleep(10)

Ten seconds pass before Drew sucks is printed to the console. In my function, I would like to provide some feedback to the user about this long pause before the pause happens.

What is causing this behavior?

Answer 1

You need to either set immediate.=TRUE to your warning function, or set options(warn=1); and may need to add flush.console() (on some operating systems) before the Sys.sleep() call.

foo <- function() {
  warning("uh-oh...", immediate.=TRUE)
  flush.console()
  Sys.sleep(5)
  "done"
}
foo()
# Warning in foo() : uh-oh...
# [1] "done"

The specifics are spelled out in the "Details" section of ?warning. To paraphrase, "if options(warn=0), warnings are stored and printed after the top-level function has completed; if options(warn=1) they are printed as they occur."