Hi ! I'm a bit confused about the official design rules for stateful transducers and transducing contexts, especially about which one should be in charge of memory visibility guarantees.
The common practice seems to be using volatiles to hold state in transducers (e.g distinct <https://github.com/clojure/clojure/blob/c0326d2386dd1227f35f46f1c75a8f87e2e93076/src/clj/clojure/core.clj#L4940>) to ensure memory visibility. This usage of volatile is actually the original motivation <http://dev.clojure.org/jira/browse/CLJ-1512> for adding it in core, and is explained further here <http://stackoverflow.com/questions/31288608/what-is-clojure-volatile> and here <http://insideclojure.org/2014/12/17/distinct-transducer/>. However, some stateful tranducers use unsynchronized mutable state instead (e.g partition-all <https://github.com/clojure/clojure/blob/c0326d2386dd1227f35f46f1c75a8f87e2e93076/src/clj/clojure/core.clj#L7123>), which goes against the previous volatile argument of "safely publish values between threads". In practice, partition-all works fine in e.g core.async because each call to the (maybe stateful) step function is made inside the channel lock. So my question is, does it make any sense at all to have a transducing context that does *not* enforce a *happens-before* order between successive calls to the step function ? If yes, I would be curious to see an example, and that would mean partition-all is broken. If no, what is the point of using volatiles for stateful transducers ? As long as they are not exposed to the outside, unsynchronized variables would do the job and should be slightly faster. Am I missing something ? Thanks Leo -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
