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. 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