Evaluate an R expression and interrupts it if it takes too long
Evaluate an R expression and interrupts it if it takes too long.
withTimeout(expr, substitute=TRUE, envir=parent.frame(), timeout, cpu=timeout,
elapsed=timeout, onTimeout=c("error", "warning", "silent"), ...)expr |
The R expression to be evaluated. |
substitute |
If |
envir |
The |
timeout, cpu, elapsed |
A |
onTimeout |
A |
... |
Not used. |
This method utilizes setTimeLimit() by first setting the
timeout limits, then evaluating the expression that may or may not
timeout. The method is guaranteed to reset the timeout limits to be
infinitely long upon exiting, regardless whether it returns normally
or preemptively due to a timeout or an error.
Returns the results of the expression evaluated.
If timed out, NULL is returned if onTimeout was
"warning" or "silent".
If "error" a TimeoutException is thrown.
In order to understand when this function works and when it does not,
it is useful to know that it utilizes R's built-in time-out mechanism,
which sets the limits on what is possible and not.
From setTimeLimit(), we learn that:
"Time limits are checked whenever a user interrupt could occur. This will happen frequently in R code and during Sys.sleep(*), but only at points in compiled C and Fortran code identified by the code author."
More precisely, if a function is implemented in native code (e.g. C) and the developer of that function does not check for user interrupts, then you cannot interrupt that function neither via a user interrupt (e.g. Ctrl-C) nor via the built-in time out mechanism. To change this, you need to contact the developer of that piece of code and ask them to check for R user interrupts in their native code.
System calls via system() and system2() cannot be
timed out via the above mechanisms. However, in R (>= 3.5.0) these
functions have argument timeout providing their own independent
timeout mechanism.
Other examples of calls that do not support timeout are "atomic"
calls that may take very long such as large object allocation and
rnorm(n) where n is very large.
(*) Note that on Unix and macOS, Sys.sleep(time) will signal a
timeout error only after time seconds passed,
regardless of timeout limit (< time).
Henrik Bengtsson
[1] R help thread 'Time out for a R Function' on 2010-12-07.
https://stat.ethz.ch/pipermail/r-help/2010-December/262316.html
Internally, eval() is used to evaluate the expression and
setTimeLimit() is used to control for timeout events.
# - - - - - - - - - - - - - - - - - - - - - - - - -
# Function that takes "a long" time to run
# - - - - - - - - - - - - - - - - - - - - - - - - -
foo <- function() {
print("Tic")
for (kk in 1:100) {
print(kk)
Sys.sleep(0.1)
}
print("Tac")
}
# - - - - - - - - - - - - - - - - - - - - - - - - -
# Evaluate code, if it takes too long, generate
# a timeout by throwing a TimeoutException.
# - - - - - - - - - - - - - - - - - - - - - - - - -
res <- NULL
tryCatch({
res <- withTimeout({
foo()
}, timeout = 1.08)
}, TimeoutException = function(ex) {
message("Timeout. Skipping.")
})
# - - - - - - - - - - - - - - - - - - - - - - - - -
# Evaluate code, if it takes too long, generate
# a timeout returning NULL and generate a warning.
# - - - - - - - - - - - - - - - - - - - - - - - - -
res <- withTimeout({
foo()
}, timeout = 1.08, onTimeout = "warning")
# The same using an expression object
expr <- quote(foo())
res <- withTimeout(expr, substitute = FALSE,
timeout = 1.08, onTimeout = "warning")
# - - - - - - - - - - - - - - - - - - - - - - - - -
# Evaluate code, if it takes too long, generate
# a timeout, and return silently NULL.
# - - - - - - - - - - - - - - - - - - - - - - - - -
res <- withTimeout({
foo()
}, timeout = 1.08, onTimeout = "silent")Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.