[Seaside] updating children components

[Avi Bryant]

On May 31, 2004, at 11:51 PM, Romain Robbes wrote:

> Hi Avi,
>
> Thanks for your answer. Is the requirement for #children to return the 
> same
> value applicable only across each call to #render in WARenderLoop ?
> If so, I might as a temporary hack add a first traversal to tell my 
> components
> to <<freeze>> during rendering.

Well, that's accurate, but it's trickier than it seems because #render 
has a continuation capture in the middle of it.  A better way of 
stating the requirement is this:

When #children is called immediately while processing a set of 
callbacks, it should return the same set of subcomponents that were 
rendered when those same callbacks were initially registered, taking 
into account that StateHolders and other backtracked objects will have 
rolled back their state appropriately.

So there's actually not a continuous span of chronological time within 
which you can freeze updates to the components: especially given the 
use of the back button, an arbitrary amount of time might have passed 
between the HTML response during which the callbacks were registered, 
and the corresponding request where they are processed, and other 
response/request pairs may have happened in the meantime.

Given that, here's something that might work for you:

- make sure all of your child state is backtrackable, eg, by using 
StateHolders to hold onto your subcomponent instances or collections of 
them (in which latter case, only use immutable collections).
- freeze updates during the request processing phase, ie, the last two 
lines of WARenderLoop>>render:

	root decorationChainDo: [:ea | ea processRequestInputs: request 
context: context].
	root decorationChainDo: [:ea | ea processRequestActions: request 
context: context]

There's still a faint possibility that an update could occur in the 
instant between the StateRegistry snapshot being restored and the 
freeze beginning, but given Squeak's concurrency model I think it's 
unlikely to happen.

Avi