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clojurestm

Clojure dosync inside future vs future inside dosync

I have the following piece of code

(def number (ref 0))

(dosync (future (alter number inc)))  ; A
(future (dosync (alter number inc)))  ; B

The 2nd one succeeds, but the first one fails with no transaction is running. But it is wrapped inside a dosync right?

Does clojure remember opening of transactions based on which thread it was created in ?

Solution

  • You are correct. The whole purpose of dosync is to begin a transaction in the current thread. The future runs its code in a new thread, so the alter in case A is not inside of a dosync for its thread.

    For case B, the alter and dosync are both in the same (new) thread, so there is no problem.