A Clojure wrapper over Failsafe
(require '[diehard.core :as diehard])
(diehard/with-retry {:retry-on IOException}
;; your code here
)
If the return value of or exception thrown from the code block matches the criteria of your retry policy, the code block will be executed again, until it mismatch the retry policy or matches the abort criteria. The block will return or throw the value or exception from the last execution.
:retry-whenretry when return value is given value:retry-onretry on given exception / exceptions(vector) were thrown:retry-ifspecify a function(fn [return-value exception-thrown]), retry if the function returns true
:abort-whenabort retry when return value is given value:abort-onabort retry on given exception / exceptions(vector) were thrown:abort-ifspecify a function(fn [return-value exception-thrown]), abort retry if the function returns true:max-retriesabort retry when max attempts reached:max-durationabort retry when duration reached
:backoff-msspecify a vector[initial-delay-ms max-delay-ms multiplier]to control the delay between each retry, the delay for nth retry will be(max (* initial-delay-ms n) max-delay-ms):delay-msuse constant delay between each retry:jitter-factorrandom factor for each delay:jitter-msrandom time(-jitter-ms, jitter-ms)adds to each delay
You can put together all those retry policies in a defretrypolicy.
(diehard/defretrypolicy policy
{:max-retries 5
:backoff-ms [1000 10000]})
(diehard/with-retry {:policy policy}
;; your code here
):on-abortaccepts a function which takesresult,exceptionas arguments, called when retry aborted:on-completeaccepts a function which takesresult,exceptionas arguments, called when exitingretryblock:on-failed-attemptaccepts a function which takesresult,exceptionas arguments, called when execution failed (matches retry criteria):on-failureaccepts a function which takesresult,exceptionas arguments, called when existingretryblock with failure (matches retry criteria):on-successaccepts a function which takesresultas arguments, called when existingretryblock with success (mismatches retry criteria):on-retryaccepts a function which takesresultas arguments, called when a retry attempted.
(diehard/deflistener listener
{:on-retry (fn [return-value exception-thrown] (println "retried"))})
(diehard/with-retry {:policy policy :listener listener}
;; your code here
):fallbackfallback value or handler function when retry blocks exists with failure.
;; return 5 when attempts failure
(with-retry {:fallback 5}
;; ...
)
;; return fallback handler function result when failed
(with-retry {:fallback (fn [value exp]
;; value: value returned from last attempt
;; exp: exception thrown from last attempt
)}
;; ...
)
(require '[diehard.core :as diehard])
(diehard/defcircuitbreaker test-cb {:failure-threshold-ratio [35 50]
:delay-ms 1000})
(diehard/with-circuit-breaker test-cb
;; your protected code here
)In this scenario, if the circuit breaker protected code block fails 35
times in 50 executions, as defined in :failure-threshold-ratio, the
test-cb is entering into :open state. When circuit breaker is
open, all execution requests will be rejected immediately.
After :delay-ms, the circuit breaker will be :half-open. At the
moment, 50 execution will be allowed, to test the state to see if it's
recovered. If success, the circuit breaker is back to :closed
state. Otherwise, it will be :open again.
You can always check circuit breaker state with
diehard.circuitbreaker/state.
There options are available when creating circuit breaker in
defcircuitbreaker.
All the three fail options share same meaning with similar option in
retry block.
:fail-if:fail-on:fail-when:timeout-mswhile give all you code a timeout is best practice in application level, circuit breaker also provides a timeout for marking a long running block as failure
:delay-msrequired. the delay for:opencircuit breaker to turn into:half-open.:failure-threshold:failure-threshold-ratio:success-threshold:success-threshold-ratioAll these four option is to determine at what condition the circuit breaker is open.
:on-opena function to be called when state goes:open:on-closea function to be called when state goes:closed:on-half-opena function to be called when state goes:half-open
The API is pretty simple but you can still find API docs here.
Copyright © 2016 Ning Sun
Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.