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mdelaurentis/memotest.clj

Created March 7, 2018 15:51
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Does clojure.core.memoize cache exceptions?
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memotest.clj
(ns memotest │
(:require [clojure.core.memoize :as memo]) │
(:import [java.util Date])) │
│
(defn memo-test-impl [] │
(when (< 0.5 (rand)) │
(throw (Exception. (str (java.util.Date.))))) │
(str (java.util.Date.))) │
│
(def memo-test (memo/ttl #'memo-test-impl :ttl/threshold 5000)) │
│
(def runner │
(future │
(while true │
(Thread/sleep 1000) │
(try │
(println "Real value returned at" (memo-test)) │
(catch Exception e │
(println "Exception thrown at" (.getMessage e))))))) │
│
#_ (future-cancel runner)
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mdelaurentis commented Mar 7, 2018 •
edited
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memo-test-impl is a memoized function that does one of two things at random:

  • With 50% probability, throws an Exception with the current time as the message
  • With 50% probability, returns a string containing the current time

The "runner" future periodically calls memo-test in a try/catch and prints the result.

Here's typical output:

Real value returned at Wed Mar 07 11:11:34 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:34 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:34 EST 2018                                                                                                                                           │Exception thrown at Wed Mar 07 11:11:39 EST 2018                                                                                                                                              │
Real value returned at Wed Mar 07 11:11:40 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:40 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:40 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:40 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:44 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:44 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:44 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:44 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:44 EST 2018                                                                                                                                           │Exception thrown at Wed Mar 07 11:11:49 EST 2018                                                                                                                                              │
Exception thrown at Wed Mar 07 11:11:50 EST 2018                                                                                                                                              │Exception thrown at Wed Mar 07 11:11:51 EST 2018                                                                                                                                              │
Real value returned at Wed Mar 07 11:11:52 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:52 EST 2018                                                                                                                                           │
Exception thrown at Wed Mar 07 11:11:54 EST 2018                                                                                                                                              │Exception thrown at Wed Mar 07 11:11:55 EST 2018                                                                                                                                              │
Real value returned at Wed Mar 07 11:11:56 EST 2018                                                                                                                                           │Real value returned at Wed Mar 07 11:11:56 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:56 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:59 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:59 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:59 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:59 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:11:59 EST 2018                                                                                                                                           │
Exception thrown at Wed Mar 07 11:12:04 EST 2018                                                                                                                                              │
Real value returned at Wed Mar 07 11:12:05 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:05 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:05 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:05 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:09 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:09 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:09 EST 2018                                                                                                                                           │
user>                                                                                                                                                                                         │
Real value returned at Wed Mar 07 11:12:09 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:09 EST 2018                                                                                                                                           │
Real value returned at Wed Mar 07 11:12:14 EST 2018

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