Executes a function later — later • later

Schedule an R function or formula to run after a specified period of time. Similar to JavaScript's setTimeout function. Like JavaScript, R is single-threaded so there's no guarantee that the operation will run exactly at the requested time, only that at least that much time will elapse.

later(func, delay = 0, loop = current_loop())

Arguments

func: A function or formula (see rlang::as_function()).
delay: Number of seconds in the future to delay execution. There is no guarantee that the function will be executed at the desired time, but it should not execute earlier.
loop: A handle to an event loop. Defaults to the currently-active loop.

Value

A function, which, if invoked, will cancel the callback. The function will return TRUE if the callback was successfully cancelled and FALSE if not (this occurs if the callback has executed or has been cancelled already).

Details

The mechanism used by this package is inspired by Simon Urbanek's background package and similar code in Rhttpd.

Note

To avoid bugs due to reentrancy, by default, scheduled operations only run when there is no other R code present on the execution stack; i.e., when R is sitting at the top-level prompt. You can force past-due operations to run at a time of your choosing by calling run_now().

Error handling is not particularly well-defined and may change in the future. options(error=browser) should work and errors in func should generally not crash the R process, but not much else can be said about it at this point. If you must have specific behavior occur in the face of errors, put error handling logic inside of func.

Examples

# Example of formula style
later(~cat("Hello from the past\n"), 3)

# Example of function style
later(function() {
  print(summary(cars))
}, 2)