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 - 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 - 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 - 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. 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