Retry expression on failure

retry() retries, upon failure, the evaluation of an expression exp for ntimes times waiting an increasing amount of time between tries, i.e., waiting for Sys.sleep(i * sleep_mult) seconds between each try i. If expr fails for ntimes times an error will be thrown.

Usage

retry(
  expr,
  ntimes = 5L,
  sleep_mult = 0L,
  retry_on = "*",
  warningsAsErrors = FALSE,
  verbose = FALSE,
  ...
)

Arguments

expr

Expression to be evaluated.

ntimes

integer(1) with the number of times to try.

sleep_mult

numeric(1) multiplier to define the increasing waiting time (in seconds).

retry_on

character(1) pattern for the error message to retry expr. Defaults to retry_on = "*" hence retrying expr on any error that occurs. This allows to restrict retrying expr for specific cases, such as temporary internet connection problems. The pattern defined by retry_on is directly passed to the grepl() function.

warningsAsErrors

logical(1) whether warnings should be converted to errors. Defaults to warningsAsErrors = FALSE.

verbose

logical(1) whether additional messages on eventually caught errors should be printed. Defaults to verbose = FALSE.

...

optional parameters passed to grepl().

Note

Warnings are suppressed.

Author

Johannes Rainer, Gabriele Tomè

Examples

## In the example below content is read from a web page that might
## temporarily be offline. It is assumed that the error message contains
## the pattern `"temporarily"` in which case the call is repeated 7 times
## with an increasing interval between tries to allow the resource to
## become available again.
if (FALSE) { # \dontrun{
    res <- retry(readLines("https://some-unreliable-web-content"),
                 retry_on = "temporarily", ntimes = 7L, sleep_mult = 10)
} # }