On Sunday, April 5, 2015 at 9:13:57 PM UTC+10, whodidthis wrote:
> On Saturday, April 4, 2015 at 7:10:00 AM UTC+3, Mike Thompson wrote:
> > So the problem sequence would be:
> > 1. first event handler called with db snapshot
> > 2. sync-dispatch called, making changes to app-db
> > 3. first event handler finishes, and the value it returns is written
> > into app-db
> >
> > The changes in step 2 are lost.
>
> I tried to replicate this but with no luck:
> (register-handler
> ::input-change
> (fn [db [_ value]]
> (println "input changed to" value)
> (assoc db :my-value value)))
> (register-handler
> ::badtimes
> (fn [db _]
> (let [my-future (+ (.getTime (js/Date.)) 3000)]
> (println "badtimes START")
> (loop []
> (if (< (.getTime (js/Date.)) my-future)
> (recur)))
> (println "badtimes END")
> (assoc db :badtimes my-future))))
>
> ::badtimes called with dispatch, ::input-change called with dispatch-sync
> while badtimes running i get:
>
> badtimes START
> badtimes END
> input change to a
> input change to ab
> input change to abc... etc
>
> Since handler functions are always synchronous could the warnings on
> dispatch-sync be a non-issue? Dispatch-synced events get in front of the line
> but they still have to wait for the current handler call to end. So there
> should be no problems as everyone gets the new db snapshot. Unless i'm
> missing something huge
What I'm saying is that you can't use dispatch-sync inside an event handler ...
(register-handler
:a
(fn [db _]
(assoc db :a 100)))
(register-handler
:b
(fn [db _]
(dispatch-sync [:a]) ;; <-- problem - change is lost
(assoc db :b 5)))
If you:
(dispatch [:b])
then afterwards, in app-db:
- :b will have a value of 5
- the change to :a (to 100) will not be there
--
Mike
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