Ding! You said the magic words! For queues, can I recommend one of the following?
http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/BlockingQueue.html According to Rich "why doesn't Clojure provide queues? The Java ones are just fine! Use them" Also, if you have a large number of queues and don't want to tie up threads, have a look a core.async (http://github.com/clojure/core.async) it's designed exactly for this sort of thing. With either of these you may still have some fun with having shared state between the threads, but perhaps these approaches may help a bit. Timothy On Thu, Aug 1, 2013 at 7:21 AM, Mike Drogalis <madrush...@gmail.com> wrote: > Unfortunately, my problem is not one where the operation is communitive. > To be concrete, > I am dealing with multiple threads plucking elements off the top of many > different queues, and > putting them into a new queue. So adding element A, then B results in line > [A, B], whereas > adding element B, then A results in line [B, A], which aren't equal. > > Maybe I'm misunderstanding my problem, perhaps it is communitive. I just > don't see it though. > > > On Thu, Aug 1, 2013 at 9:13 AM, Timothy Baldridge <tbaldri...@gmail.com>wrote: > >> " >> 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." >> >> That's not the problem. The problem is that agent sends (just like >> watchers) are dispatched outside of the transaction. So multiple threads >> accessing the same refs can be releasing sends to agents at the same time. >> This in turn means that the messages being sent to the agents can arrive >> out-of-order since one thread could pause allowing the other to send >> messages. >> >> Something to think about though is that you probably should be dealing >> with commutative operations. So instead of sending "set bank account to X" >> to refs/agents, instead send "increment bank account by 10". In this way >> many of these race-conditions no longer exist. >> >> Timothy >> >> >> On Thu, Aug 1, 2013 at 6:54 AM, Mike Drogalis <madrush...@gmail.com>wrote: >> >>> Cedric: Will agents give me the guarantee that if I have something in >>> Agent A, and I want to move it to agent B, and I do this inside a >>> transaction: >>> - perceivers will see it in A at read point >>> - perceivers will see it in B at write point >>> - perceivers will never see it in neither nor both? >>> >>> If that's the case, which is effectively synchronous coordination (I >>> think?), what do refs buy you that agents don't? >>> >>> >>> On Thu, Aug 1, 2013 at 5:57 AM, Cedric Greevey <cgree...@gmail.com>wrote: >>> >>>> 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 - 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. >>>>>> 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. >>>>> >>>>> >>>>> >>>> >>>> -- >>>> -- >>>> 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. 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.
