Clojurians Log v2

Guys how so mount doesn’t support async start/stop. For example, if I need to load config asynchronously. How is that usually handled?

@madvas can you describe what you are trying to do?

(and why)

I need to load some configuration from locally running blockchain (understand server). Cannot be done in sync way. Other components might need this configuration data in their :start function

so other components won't be able to start until the config is loaded?

no, they need loaded information

right, so what makes it async?

not sure what you mean. that request to locally running server to fetch config. It’s separate app from the cljs app

ok, so you have two apps?

one in cljs and another one is clj (i.e. backend)

and you need to load configuration from the server whenever someone visits a page / or the cljs app starts?

no, it’s different. Have just one, it’s cljs nodejs app, the other one is blockchain, it’s 3rd party software beyond my control

ok, and you need to load config from a 3rd party app (i.e. a server) on cljs nodejs app's start?

yes

mount will respect the order of states that need to be started, which means components which need this configuration will wait until a component that loads it from the server is started. i.e. if you have something like:

(defstate config :start (load-it-from-server "<http://localhost:8080/config>"))

from what you described so far I don't see what is "async" about it

but load-it-from-server returns what? you mean to do it like synchronous load?

the thing is that library to interact with blockchain server doesn’t support synchronous requests. Must pass callback

right, so you can put it in a channel once the response is received. pseudo code:

(let [c (async/chan)]
  (http/get url #(>!! c %))
  (<!! c))

I would wrap it in a load-it-from-server function, with a better name of course

there’s no >!! and <!! in cljs

only non-blocking

ah.. cljs that's right, single event loop. then you would provide a callback that does (mount/start). once the config is loaded, mount will start all the components

I see, that’s what I started thinking, okay I’ll figure out something, thank you very much for your time 😉

sure, sorry took some time to understand where you are coming from

something that can be useful: (-> (with-args {:config ....}) (mount/start))

since once you receive the config you need to pass it to all other components

i.e. https://github.com/tolitius/mount#composers-toolbox

yeah, I have that in mind, thanks but would be nice if I could just pass channel or something to defstate and it would wait with execution until results come and then pass it

might be useful only for cljs side. and not in defstate, since the waiting should happen outside of mount: i.e. before calling (mount/start)

I think there’s more use cases where async start might be useful and cannot be done before mount/start. But yeah, clj’s advantage over cljs here is that it can make any asynchronous call synchronous