after: Run Code in the Background
In after: Run Code in the Background

Description Usage Arguments Details Value Additional methods Examples

Run an R function in the background, possibly after a delay. The current version uses the Tcl event loop. It was inspired by similar functionality in the tcltk2 package.

after(ms, fun, args = list(), redo = 0)

## task <- after(ms, fun, args = list())
## after$info(task)
## after$list()
## after$cancel(task)

`ms`	Amount of time to wait before running the function, in milliseconds. An integer scalar. Use zero for immediate execution.
`fun`	Function to run. Note that the function is run in the global environment, so it is good practice not to use functions from packages directly. See the examples below.
`args`	Arguments to pass to the function, a list. As the function runs in the global environment, it does not have access to the objects in the calling environment. But you can pass arguments to it here.
`redo`	How many times to re-run the function. Zero means running it only once, and `Inf` means re-running it continuously, until the R session is closed, the task is canceled, or the `after` package is unloaded.
`task`	Task id.

Note that this does not mean parallelism. The scheduled function runs in the main R process, after the specified time, whenever R is free of other work. Also, while the scheduled function runs, no other R computation can be done. If you use R interactively, then your command prompt will “freeze” while the scheduled function runs.

Thus, after is best for running very short processes, at least for interactive use.

A task id that you can use in after$info and after$cancel. It is returned invisibly.

after$info(task) will display some information about the task.

after$list() lists all scheduled tasks.

after$cancel(task) cancels a task.

# simple example, runs after a second
after(1000, function() cat("Here I am!\n"))

# supplying arguments
x <- "print me!"
after(1000, function(x) print(x), args = list(x))
# we can remove x now, it is already stored in the timer
rm(x)

# calling functions in packages
# Instead of after(1000, utils::alarm) use
after(1000, function() utils::alarm())
# in case utils::alarm() uses other functions from the
# utils package.

# repeat a task
x <- after(1000, function() print("still here"), redo = 5)
Sys.sleep(3)

# list tasks
after$list()

# cancel a task
after$cancel(x)