Robert Bruce provides an easy way to execute a function and allow failures to be automatically retried. It's named after Robert the Bruce, whose determination was inspired by the sight of a spider trying (and failing) many times to build a web.
Add this to your project.clj :dependencies list:
[robert/bruce "0.7.1"]
(use '[robert.bruce :only [try-try-again]])
;; arguments are like trampoline, if you want the default options
(try-try-again some-fn)
(try-try-again some-fn arg1 arg2)
(try-try-again #(some-fn arg1 arg2))
;; but with the addition of a first options arg, if you don't
(try-try-again {:sleep 5000 :tries 100} #(some-fn arg1 arg2))
(try-try-again {:sleep nil :tries 100} #(some-fn arg1 arg2))
(try-try-again {:decay :exponential :tries 100} #(some-fn arg1 arg2))
(try-try-again {;; all options are optional
;; :sleep is used to specify how long to sleep
;; between retries, it can be a number, or false
;; or nil if you don't want to sleep,
;; default is 10 seconds (that is, 10000)
:sleep 100
;; :tries is used to specific how many tries
;; will be attempted, it can also be :unlimited
;; default is 5
:tries 100
;; if you want your sleep amount to change over
;; time, you can provide a decay function:
;; a number - your sleep will be multiplied by it
;; a function - your sleep will passed into it
;; a keyword - for out of the box decay algorithms
;; :exponential, :double, :golden-ratio
;; default is identity
:decay :exponential
;; if you want to only retry when particular
;; exceptions are thrown, you can add a :catch
;; clause. it works with either a single type
;; or a collection.
;; default is Exception
:catch [java.io.IOException java.sql.SQLException]
;; if you would like a function to be called on
;; each failure (for instance, logging each failed
;; attempt), you can specify an error-hook.
;; The error that occurred is passed into the
;; error-hook function as an argument.
;; The error-hook method can also force a
;; short-circuit failure by returning false, or
;; force an additional retry by returning true.
:error-hook (fn [e] (println "I got an error:" e))}
#(some-fn arg1 arg2))
;; In addition, four dynamic variables are bound in both the
;; passed in and error-hook functions:
;; *first-try* - true if this is the first try
;; *last-try* - true if this is the last try
;; *try* - the current try number (starting at 1)
;; *error* - the last error that occurred
;; you can also use metadata on the function itself
(try-try-again ^{:decay :exponential :tries 100} #(some-fn arg1 arg2))Copyright (C) 2011 Joe Gallo
Distributed under the Eclipse Public License, the same as Clojure.