On Mon, Nov 3, 2014 at 5:57 PM, Daniel Marjenburgh <dmarjenbu...@gmail.com> wrote:
> Hi, > > I just want to address this issue (CLJ-1498 > <http://dev.clojure.org/jira/browse/CLJ-1498>). It was accepted in > 1.7-alpha2 and I haven't seen a lot of discussion around it, even though > it's quite a big change. > > With this change the following code is possible: > With persistents the result would be the same, every time. If this is now valid Clojure, I didn't run it myself, we are sacrificing consistency. I don't understand what we're getting in return. Even the simple example in the ticket (with one future) doesn't make a lot of sense to me. Am I missing something obvious? > > (let [m (transient {:a 0}) > futs (for [n (range 100)] > (future (assoc! m :a (inc (:a m)))))] > (mapv deref futs) ; wait until futures are done > (persistent! m)) > > > The results will vary per run, where it used to throw > an IllegalAccessError: "Transient used by non-owner thread". > > I understand the problems of not being able to have 1 go routine access a > transient, even though it would be safe, but this solution feels like it's > throwing out the baby with the bathwater. Basically, it's doing away with > what the following block on clojure.org <http://clojure.org/transients> > says: > > *Transients enforce thread isolation**.* Because each result of a >> transient operation shares (mutable) structure with the previous, it would >> be very dangerous if more than one thread were to manipulate a transient at >> once. In order to prevent this, transients will detect any (read or write) >> use from a thread other than the one that created them and throw an >> exception. > > > >> >> This may not sound like a concurrency story, but single-thread isolation >> is actually a very useful concurrency semantic. The whole point of using >> transients is that doing so is safe, because their use is an isolated >> implementation detail of otherwise functional code. Having that be enforced >> means that some things that would normally be very hard to make safe with >> ordinary mutable data structures become easy. > > > I don't have a good solution for dealing with transients and logical > threads, but I would much prefer keeping the semantics of transients as > they are and maybe pass an option to transient to disable owner checking. > > -- > 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. > -- Kind Regards, Atamert Ölçgen -+- --+ +++ www.muhuk.com -- 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.
