Transform a function to make it run insistently or slowly

• insistently() takes a function and modifies it to retry a given amount of time on error.

• slowly() takes a function and modifies it to wait a given amount of time between each call.

The number and rate of attempts is determined by a rate object (by default a jittered exponential backoff rate for insistently(), and a constant rate for slowly()).

insistently(f, rate = rate_backoff(), quiet = TRUE)

slowly(f, rate = rate_delay(), quiet = TRUE)

Arguments

f	A function to modify.
rate	A rate object determining the waiting time.
quiet	If FALSE, prints a message displaying how long until the next request.

See also

httr::RETRY() is a special case of insistently() for HTTP verbs. rate_backoff() and rate_delay() for creating custom backoff rates. rate_sleep() for the function powering insistently() and slowly(). safely() for another useful function operator.

Examples

# For the purpose of this example, we first create a custom rate
# object with a low waiting time between attempts:
rate <- rate_delay(0.1)

# slowly() causes a function to sleep for a given time between calls:
slow_runif <- slowly(~ runif(1), rate = rate, quiet = FALSE)
map(1:5, slow_runif)
#> Retrying in 0.1 seconds.
#> Retrying in 0.1 seconds.
#> Retrying in 0.1 seconds.
#> Retrying in 0.1 seconds.
#> [[1]]
#> [1] 0.7353196
#> 
#> [[2]]
#> [1] 0.1959567
#> 
#> [[3]]
#> [1] 0.9805397
#> 
#> [[4]]
#> [1] 0.7415215
#> 
#> [[5]]
#> [1] 0.05144628
#> 


# insistently() makes a function repeatedly try to work
risky_runif <- function(lo = 0, hi = 1) {
  y <- runif(1, lo, hi)
  if(y < 0.9) {
    stop(y, " is too small")
  }
  y
}

# Let's now create an exponential backoff rate with a low waiting
# time between attempts:
rate <- rate_backoff(pause_base = 0.1, pause_min = 0.005, max_times = 4)

# Modify your function to run insistently.
insistent_risky_runif <- insistently(risky_runif, rate, quiet = FALSE)

set.seed(6) # Succeeding seed
insistent_risky_runif()
#> Error: 0.606268297648057 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.264352067606524 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.807483389042318 is too small
#> Retrying in 0.8 seconds.
#> [1] 0.9579337

set.seed(3) # Failing seed
try(insistent_risky_runif())
#> Error: 0.168041526339948 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.384942351374775 is too small
#> Retrying in 0.1 seconds.
#> Error: 0.602100674761459 is too small
#> Retrying in 0.5 seconds.
#> Error: 0.124633444240317 is too small
#> Error : Request failed after 4 attempts


# You can also use other types of rate settings, like a delay rate
# that waits for a fixed amount of time. Be aware that a delay rate
# has an infinite amount of attempts by default:
rate <- rate_delay(0.2, max_times = 3)
insistent_risky_runif <- insistently(risky_runif, rate = rate, quiet = FALSE)
try(insistent_risky_runif())
#> Error: 0.294600924244151 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.577609919011593 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.630979274399579 is too small
#> Error : Request failed after 3 attempts


# insistently() and possibly() are a useful combination
rate <- rate_backoff(pause_base = 0.1, pause_min = 0.005)
possibly_insistent_risky_runif <- possibly(insistent_risky_runif, otherwise = -99)

set.seed(6)
possibly_insistent_risky_runif()
#> Error: 0.606268297648057 is too small
#> Retrying in 0.2 seconds.
#> [1] 0.937642

set.seed(3)
possibly_insistent_risky_runif()
#> Error: 0.168041526339948 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.807516399072483 is too small
#> Retrying in 0.2 seconds.
#> Error: 0.384942351374775 is too small
#> [1] -99