make sure graphics device gets closed

Question

I am closing the device (here: pdf() ) I am plotting to at the end of my function with dev.off(). However, if the function/loop terminates due to an error the device stays open. When a function gets repeatedly called, this can lead to quite a lot of open devices; and file handles.

How can I make sure the device gets closed even if the function fails?

I do remember that I once saw how to do this, but I cannot remember.

Answer 1

on.exit() is made for situations just like this. It's good practice to use it whenever opening a (file or other) connection in a non-interactive setting.

f <- function() {
    pdf(tempfile()) # tempfile() so example doesn't clutter up working directory.
    on.exit(dev.off())
    plot(randomNonExistentObjectName)
}

f()
# Error in plot(randomNonExistentObjectName) : 
#   object 'randomNonExistentObjectName' not found

dev.list()
# NULL