Stop calling a function that keeps failing

Decorator that stops calling a function after it fails repeatedly, so callers fail fast instead of waiting on something that is down. It has three states:

Usage

circuit_breaker(f, failures = 5, reset_after = 30)

Arguments

f

The function to decorate. Usually supplied by %@% rather than directly.

failures

Number of consecutive errors that open the circuit. A whole number of at least 1. Defaults to 5.

reset_after

Seconds the circuit stays open before a trial call. A number greater than 0. Defaults to 30.

Value

A decorator.

Details

• closed: calls go through. Consecutive errors are counted.

• open: after failures consecutive errors, calls fail immediately with a garnish_circuit_open error, without running the function, for reset_after seconds.

• half-open: once the cooldown has passed, the next call runs as a trial. If it succeeds the circuit closes. If it fails the circuit opens again for another cooldown.

Only errors count as failures. A call that returns normally, whatever its value, resets the count. Each decorated function keeps its own state.

Stack it outside retry() so an open circuit rejects a call before any retries happen:

fetch := circuit_breaker(failures = 3, reset_after = 30) %@%
  retry(stop = stop_after_attempt(3)) %@%
  function(url) { ... }

Examples

n <- 0
flaky <- function() {
  n <<- n + 1
  stop("service down")
}
f := circuit_breaker(failures = 2, reset_after = 60) %@% flaky
try(f())
#> Error in <environment>$fn() : service down
try(f())
#> Error in <environment>$fn() : service down
try(f()) # rejected without calling flaky()
#> Error : Circuit is open: the function failed repeatedly and is not being called.
n # still 2
#> [1] 2