I am not an expert on Component. But AFAIK it is not for managing mutable
state but for assembling and configuring components, that might or might
not be mutable themselves, in an immutable fashion.
However from what I can understand, your component-a has an atom, like:
(->component-a (atom something))
Which should be OK. I mean it shouldn't matter from which path you are
accessing this atom.
Can you share the constructor/definition of the components?
Also, have you tried confirming that only one :a is instantiated?
On Wed, Apr 30, 2014 at 9:13 PM, Timothy Washington <twash...@gmail.com>wrote:
> Hi all,
>
> I'm having a weird state problem with
> Component<https://github.com/stuartsierra/component>.
> Let's say I have a system component, like in fig.1. Starting / stopping and
> loading state is fine.
> However, let's say I have 2 other components (:updater , :reader) that use
> component :a. This is the problem that occurs.
>
> 1. When *:updater*, modifies an atom in *:a*, that change appears in
> path [*:core :a*], not path [*:updater :a*] or [*:a*].
> 2. Because of the abouve, when *:reader* goes to it's local path [
> *:reader :a*] to read that change, it doesn't see those modifications.
> 3. Using this scheme, *:a* is duplicated 4 times, in the system map.
> However, the modifications only appear in path [*:core :a*]. Thus
> :reader is unable to access it (it's local [*:a*] is unchanged).
>
>
> (def system-components [:a :updater :reader])
>
> (defrecord Core [env] component/Lifecycle
> (start [this] ...)
> (stop [this] ...))
>
> (defn component-core [env]
>
> (component/system-map
> :a (component/using
> (ca/component-a env)
> {})
> :updater (component/using
> (cs/component-updater env)
> {:a :a})
> :reader(component/using
> (cs/component-reader env)
> {:a :a})
> :core (component/using
> (map->Foobar {:env env})
> {:a :a
>
> :updater :updater
>
> :reader :reader })))
>
> *fig.1 *
>
>
> I was hoping to use Component to manage all internal application state.
> But maybe it's not designed for this use case (state changes between
> components). I imagine that immutability is preventing all those duplicates
> from seeing the modifications. However, in this case I do need an update to
> :a in one component, to be accessed by another component.
>
> Any suggestions on patterns here? I'm also looking at
> component/update-system<https://github.com/stuartsierra/component/blob/master/src/com/stuartsierra/component.clj#L116>.
> But again, I don't have access to the core *system* var, from within my
> components.
>
>
> Any insights appreciated
>
> Tim Washington
> Interruptsoftware.com <http://interruptsoftware.com>
>
>
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