(defn runonce
"Create a function that will only run once. All other invocations
return the first calculated value. The function *can* have side effects
and calls to runonce *can* be composed. Deadlock is possible
if you have circular dependencies.
Returns a [has-run-predicate, reset-fn, once-fn]"
[function]
(let [sentinel (Object.)
result (atom sentinel)
reset-fn (fn [] (reset! result sentinel))
has-run-fn (fn [] (not= @result sentinel))]
[has-run-fn
reset-fn
(fn [& args]
(locking sentinel
(if (= @result sentinel)
(reset! result (function))
@result)))]))
Used in 0 other vars
Source
lancet.clj:65
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