Try using an agent send from inside a transaction. Such sends are only dispatched if the transaction commits, and successive sends to the same agent from a single thread are run by the agent in the same order the thread sent them.
On Wed, Jul 31, 2013 at 1:12 PM, Mike Drogalis <madrush...@gmail.com> wrote: > Good reasoning; that makes a lot of sense -- even if intuitively it > doesn't follow through. > > I'll do some more thinking about my concurrency needs and come back with a > follow up question later. Thanks man! > > > On Wed, Jul 31, 2013 at 12:51 PM, Timothy Baldridge > <tbaldri...@gmail.com>wrote: > >> Deadlocks? Imagine a watch that ended up running a transaction against >> the ref it was triggered from. Sounds insane, but it could be fairly easy >> to do in a situation like this: >> >> ref -> calls watchers -> calls fn1 -> calls fn 2 -> calls fn3 -> starts >> transaction on ref >> >> Since watchers are notified outside of a ref transaction deadlocking is >> impossible. Inside a transaction you'd have a instant deadlock. >> >> Timothy Baldridge >> >> >> On Wed, Jul 31, 2013 at 10:47 AM, Mike Drogalis <madrush...@gmail.com>wrote: >> >>> I'll play around with agents for this when I get some more free time. >>> >>> I find it odd that, as the sole perceiver of an indentity, events are >>> capable of being perceived out of order. >>> If I were watching a line queue up in person, events are obviously >>> "dispatched" in order through my visual perception. >>> I trust there's a good reason it's designed this way, at any rate. >>> >>> >>> On Wed, Jul 31, 2013 at 12:25 PM, Timothy Baldridge < >>> tbaldri...@gmail.com> wrote: >>> >>>> You might want to consider switching to agents (or something else) I >>>> don't think it's possible to do what you want with refs. >>>> >>>> Timothy Baldridge >>>> >>>> >>>> On Wed, Jul 31, 2013 at 10:08 AM, Mike Drogalis >>>> <madrush...@gmail.com>wrote: >>>> >>>>> Thanks for the link. :) I understand that the behavior I'm seeing is >>>>> correct. Any idea how to achieve the desired behavior, though? >>>>> >>>>> >>>>> On Wed, Jul 31, 2013 at 12:06 PM, Timothy Baldridge < >>>>> tbaldri...@gmail.com> wrote: >>>>> >>>>>> The answer is here: >>>>>> >>>>>> >>>>>> https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/LockingTransaction.java#L361 >>>>>> >>>>>> Agents and watches are dispatched outside of the transaction locking. >>>>>> This means that multiple transactions could be executing watches in >>>>>> parallel, and hence execute out of order. >>>>>> >>>>>> Timothy Baldridge >>>>>> >>>>>> >>>>>> On Wed, Jul 31, 2013 at 9:43 AM, Michael Drogalis < >>>>>> madrush...@gmail.com> wrote: >>>>>> >>>>>>> I can precisely exemplify the behavior here: >>>>>>> >>>>>>> https://gist.github.com/MichaelDrogalis/6123177 >>>>>>> >>>>>>> >>>>>>> On Wednesday, July 31, 2013 11:13:17 AM UTC-4, Michael Drogalis >>>>>>> wrote: >>>>>>>> >>>>>>>> Aaron: Yep, I'm aware - and am using the value provided by the last >>>>>>>> parameter. >>>>>>>> >>>>>>>> This is going to be tough to show the problem without bringing more >>>>>>>> details of my concurrency set up. >>>>>>>> I'm not sure if this will exhibit the problem, but this is what it >>>>>>>> boils down to: >>>>>>>> >>>>>>>> https://gist.github.com/**MichaelDrogalis/6122834<https://gist.github.com/MichaelDrogalis/6122834> >>>>>>>> >>>>>>>> When enough threads are trying to write to the queue, the watches >>>>>>>> triggered later can finish before watches triggered earlier. >>>>>>>> >>>>>>>> >>>>>>>> On Wednesday, July 31, 2013 11:05:16 AM UTC-4, Aaron Cohen wrote: >>>>>>>>> >>>>>>>>> A watcher fn has 4 parameters: key, reference, old-state, new-state >>>>>>>>> >>>>>>>>> If you use old-state and new-state rather than the reference, you >>>>>>>>> should not see your problem. >>>>>>>>> >>>>>>>>> --Aaron >>>>>>>>> >>>>>>>>> >>>>>>>>> On Wed, Jul 31, 2013 at 11:00 AM, Michael Drogalis < >>>>>>>>> madru...@gmail.com> wrote: >>>>>>>>> >>>>>>>>>> Problem: >>>>>>>>>> >>>>>>>>>> I have a ref representing a queue of people in line. >>>>>>>>>> I add a watch to the ref to print out the contents of the queue >>>>>>>>>> whenever it changes. >>>>>>>>>> Naturally, and expected, the following can happen if queuing >>>>>>>>>> happens in rapid succession: >>>>>>>>>> >>>>>>>>>> Queue: [] >>>>>>>>>> <add "Mike" to queue> >>>>>>>>>> <add "John" to queue> >>>>>>>>>> >>>>>>>>>> console: "Queue is Mike, John" >>>>>>>>>> console: "Queue is Mike" >>>>>>>>>> >>>>>>>>>> I'd like to write a UI for this program, but I clearly can't >>>>>>>>>> reliably render based on the result delivered >>>>>>>>>> by the add-watch hook. What's the solution for this problem? >>>>>>>>>> >>>>>>>>>> -- >>>>>>>>>> -- >>>>>>>>>> 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<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 <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 clojure@googlegroups.com >>>>>>> Note that posts from new members are moderated - 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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 a topic in the >>>> Google Groups "Clojure" group. >>>> To unsubscribe from this topic, visit >>>> https://groups.google.com/d/topic/clojure/0b5HWJE6Jx4/unsubscribe. >>>> To unsubscribe from this group and all its topics, send an email to >>>> clojure+unsubscr...@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 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/groups/opt_out. >>> >>> >>> >> >> >> >> -- >> “One of the main causes of the fall of the Roman Empire was that–lacking >> zero–they had no way to indicate successful termination of their C >> programs.” >> (Robert Firth) >> >> -- >> -- >> 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 - 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