Is a set state called multiple times?

[fengxia]

Tilman,

This is quite interesting, and I think that's exactly what confused me 
-- I took @when as event handler, and expected to be executed only on 
False->True transition, but not being continuously executed if I don't 
"remove_state" inside itself.


On 07/27/2017 12:29 PM, Tilman Baumann wrote:
> The confusion comes from the expectations at states are somehow events
> and @when decorators are event handlers.
> @when are predicates on states. When predicates are true the decorated
> code is executed at every hook invocation.
>
>
> If you want to trigger on edges (state changes) you need to build flipflops.
>
>
> @when("state.wanted")
> @when_not("state.reached")
>
> do stuff here when entering state
> set_state("state.reached")
>
>
> @when_not("state.wanted")
> @when("state.reached")
>
> do stuff here when leaving state
> remove_state("state.reached")
>
>
> Reactive is still quite nice after you wrapped your head around that.
>
>
> // Rant follows
>
> Shame though that ALL interfaces are broken and thus unusable.
>
> Interfaces need to be fixed on a fundamental level IMHO.
> I have a workaround proposal
> https://github.com/tbaumann/charm-interface-peer-discovery/blob/master/peers.py
> But in truth, that is not a great solution, it's just a workaround.
>
> I know I'm derailing the conversation here completely, but the
> brokenness of interfaces has been a personal annoyance for a while and I
> wish I could do something to change that.
>
> One of the issues is that one can not react on "relation.connected"
> states because the context they are supposed to have (argument to
> decorated function) only works in the right hook context.
> I propose a @interface decorator which will create the right context and
> instantiate a interface object.
> That way I can use interfaces in all sorts of functions and not only in
> hook context and the kludges around to avoid being called outside of
> hook context.
>
>
> Problems with interfaces:
> - *.connected state gets dropped when one  unit leaves. Not when the
> last one leaves.
> - self.* only works when code runs in the right hook context
> - interface class reference is only passed in decorated functions if the
> hook inside the interface code ran
> - Only the first occurrence of a unit joining a relation can be caught
> with handler
> - Interfaces have 90% identical code which is just boilerplate
>
>
>
> Just my 0.02€
>
>
> On 27.07.2017 03:37, fengxia wrote:
>> Hi Juju,
>>
>> Once I set a state, set_state("here"), I want to make sure its @when
>> will only be executed ONCE (when "here" from False->True).
>>
>> So my thought is to remove_state("here") in its @when("here") code
>> block. If I don't, will this @when be called multiple times if I don't
>> reset this state? What's the good practice here?
>>

-- 
Feng xia
Engineer
Lenovo USA

Phone: 5088011794
fxia1 at lenovo.com
  	
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