core.cache

SoftCache NullPointerException in has? with many threads

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Major Major
  • Resolution: Unresolved
  • Affects Version/s: None
  • Fix Version/s: None
  • Component/s: None
  • Labels:
    None
  • Environment:
    Linux, Oracle JRE 1.6
  • Patch:
    Code

Description

"cell" can be null on this call to SoftReference.get():
https://github.com/clojure/core.cache/blob/master/src/main/clojure/clojure/core/cache.clj#L501

If the cache did not contain "item" in the call to (get cache item) in the let binding, but another thread pre-empts and adds it before the subsequent call to contains?, we'll attempt to call .get() on nil.

Would it perhaps be sufficient to just check whether cell is nil instead of calling contains? in the check on the previous line?

Activity

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Paul Stadig added a comment - - edited

Good catch!

This is rather simple to reproduce:

(use 'clojure.core.cache)
(def cache (soft-reference-cache {}))
(def mutator (Thread. #(loop [] (assoc cache :foo :bar) (dissoc cache :foo) (recur))))
(.start mutator)
(loop [] (has? cache :foo) (recur))

The attached patch fixes the issue, by not referring back to the cache after attempting to pull out a SoftReference.

Show
Paul Stadig added a comment - - edited Good catch! This is rather simple to reproduce:
(use 'clojure.core.cache)
(def cache (soft-reference-cache {}))
(def mutator (Thread. #(loop [] (assoc cache :foo :bar) (dissoc cache :foo) (recur))))
(.start mutator)
(loop [] (has? cache :foo) (recur))
The attached patch fixes the issue, by not referring back to the cache after attempting to pull out a SoftReference.

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Dates

  • Created:
    Updated: