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favila/tempid-idx.clj

Created June 1, 2015 23:26
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AtomicInteger counter with overflow handled correctly
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tempid-idx.clj
(import '[java.util.concurrent.atomic AtomicInteger])
(set! *unchecked-math* :warn-on-boxed)
(def ^AtomicInteger counter (AtomicInteger.))
(defn next-tempid-idx [^AtomicInteger i]
(unchecked-subtract -1000000 (bit-and (.getAndIncrement i) 0x7fffffff)))
(next-tempid-idx counter)
;=> -1000000
(next-tempid-idx counter)
;=> -1000001
(next-tempid-idx counter)
;=> -1000002
(.set counter Integer/MAX_VALUE)
;=> nil
(next-tempid-idx counter)
;=> -2148483647
(next-tempid-idx counter)
;=> -1000000
(next-tempid-idx counter)
;=> -1000001
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