Hi t x and Jan, what about performing the side effect part of the function adding a watch? (They are no more in alpha with the upcoming 1.6.)
Cheers, Luca Il giorno lunedì 17 febbraio 2014 09:29:57 UTC+1, t x ha scritto: > > Hi Jan, > > Thanks for your explanations. > > I have no idea how I managed to completely misunderstand > clojure/atom for the past few years -- I suspect it's because I never > use clojure/STM, and as a result, I've never had an atom roll back on > me. > > I've decided to switch to agents. > > Thanks again for catching this fundamental error. > > > > On Sun, Feb 16, 2014 at 11:00 PM, Jan Herich > <jan.h...@gmail.com<javascript:>> > wrote: > > Hi t x, > > > > I think, that lock-free approach an it's semantics is more in line with > > other Clojure reference types such as refs. > > It also encourages you to only use pure functions for state transitions, > > among other things, such as significant > > performance benefits in comparison with lock based approaches, see for > > example this article. > > If you really want to update some reference with function which will > also > > perform "impure" actions such as file I/O, > > consider using agents and send or send-off (the latter in case of I/O > > blocking actions), functions given to send > > and send-off are guaranteed to run only once. > > > > Dňa pondelok, 17. februára 2014 2:36:59 UTC+1 t x napísal(-a): > >> > >> Hi Jan, > >> > >> You're right. I'm wrong. > >> > >> I'm grateful you pointed this out -- this would have otherwise been > >> impossible to debug. > >> > >> =========================== > >> > >> To everyone: > >> > >> Why can swap! be retried? This confuses me -- to implement swap!, why > >> can't we > >> > >> * have a lock > >> > >> * ensure that only one swap! is in session at any given time > >> > >> * have the given swap! complete before running the next swap! > >> > >> > >> Thanks! > >> > >> > >> On Sun, Feb 16, 2014 at 3:51 PM, Jan Herich <jan.h...@gmail.com> > wrote: > >> > I'm afraid your understanding of atom swap! operations is not quite > >> > correct > >> > -> update function must (or should) be pure as well. > >> > See the documentation for swap!, update function could be potentially > >> > called > >> > multiple times if there are more threads of execution > >> > updating one atomic reference -> there is simple compare and set > >> > mechanism > >> > involved, which compares the old value of the atom > >> > (input for the update function) and sets the atom to new value > (return > >> > value > >> > from the update function) only value of the atom reference > >> > was not changed in between, if yes the compare and set is retried > until > >> > ti > >> > succeeds. > >> > > >> > Dňa nedeľa, 16. februára 2014 23:35:24 UTC+1 t x napísal(-a): > >> >> > >> >> I believe that's the STM approach, which has the advanrtage of: > >> >> > >> >> * can synchronize across multiple pieces of data > >> >> > >> >> but has the disadvantage of: > >> >> > >> >> * work must be "pure" since it can be retried > >> >> > >> >> * possibly less efficient due to possibility of retrying > >> >> > >> >> > >> >> In the example I posted above, I only need to: > >> >> > >> >> * modify a single atom > >> >> > >> >> and the approach I presented above: > >> >> > >> >> * can be impure, since it is guaranteed to only run once > >> >> > >> >> * is guaranteed to succeed (without retrys) > >> >> > >> >> On Sun, Feb 16, 2014 at 2:25 PM, Ramesh <ramesh1...@gmail.com> > wrote: > >> >> > You can use a ref instead of an atom. And use dosync with multiple > >> >> > alter, so > >> >> > everything is safely inside a transaction. > >> >> > > >> >> > On Feb 16, 2014 2:04 PM, "t x" <txre...@gmail.com> wrote: > >> >> >> > >> >> >> Hi John, > >> >> >> > >> >> >> Your solution is perfectly valid and optimal for the problem I > >> >> >> described above. > >> >> >> > >> >> >> > >> >> >> Unfortunately, I forgot to mention an additional constraint: > >> >> >> sometimes I > >> >> >> do: > >> >> >> > >> >> >> (let [ foo (:some-selector @data-atom) ] > >> >> >> (swap! data-atom update-in [:other-selector] ... )) > >> >> >> > >> >> >> which the -> doesn't quite work on, but my ugly hack above does > >> >> >> resolve. > >> >> >> > >> >> >> > >> >> >> The problem being -- I want to update one part of the atom, but > it > >> >> >> depends on another part of the atom. > >> >> >> > >> >> >> I ended up with the following hack: > >> >> >> > >> >> >> (defn tswap! [atm func] > >> >> >> (swap! atm > >> >> >> (fn [old] > >> >> >> (let [natm (atom old)] > >> >> >> (func natm) > >> >> >> @natm)))) > >> >> >> > >> >> >> > >> >> >> On Sat, Feb 15, 2014 at 4:09 PM, John D. Hume < > duelin....@gmail.com> > >> >> >> wrote: > >> >> >> > On Sat, Feb 15, 2014 at 6:04 PM, t x <txre...@gmail.com> > wrote: > >> >> >> >> > >> >> >> >> > >> >> >> >> (defn what-I-want [] > >> >> >> >> (with-atom some-atom > >> >> >> >> assoc-in ... > >> >> >> >> assoc-in ... > >> >> >> >> update-in ...)) > >> >> >> > > >> >> >> > > >> >> >> > I often do something like this and don't find it too ugly: > >> >> >> > (swap! my-atom #(-> % > >> >> >> > (assoc-in [:k] v) > >> >> >> > (update-in [:k2] inc) > >> >> >> > ,,,)) > >> >> >> > > >> >> >> > -- > >> >> >> > You received this message because you are subscribed to the > Google > >> >> >> > Groups "Clojure" group. > >> >> >> > To post to this group, send email to clo...@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+u...@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+u...@googlegroups.com. > >> >> >> > For more options, visit > https://groups.google.com/groups/opt_out. > >> >> >> > >> >> >> -- > >> >> >> You received this message because you are subscribed to the > Google > >> >> >> Groups "Clojure" group. > >> >> >> To post to this group, send email to clo...@googlegroups.com > >> >> >> Note that posts from new members are moderated - 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