On Jul 14, 2006, at 12:43 PM, Jeremy Boynes wrote:
The Java implementation model allows components to designate that
they are "eager" init which means that they will be initialized
when the composite they are in is started rather than on first use.
One problem that I ran into with the extension stuff is that the
specification does not say or even allow a user to say in which
order the components will be started.
One option would be to follow a lexical convention and say that
components will be started in the order that they appear in the
SCDL. I have a few reservations about this:
* users may have other criteria for laying out the file (for
example grouping components together)
* this can be confusing in the presence of include elements - users
may want to group
components together in an include that would fit in different
places in the start order
This can also be dangerous if a tool doesn't preserve the exact order
or someone inadvertently changes something.
Instead I'd like to propose we support an init-level indicator like
the run level from Unix systems. Components would be started in
ascending order of the init level they provided.
This could be done as an attribute on the <component> element,
something like:
<component name="start2nd" initLevel="20"> ...
<component name="start1st" initLevel="10"> ...
This would also allow us to eagerly initialize components without
having to use an @Init annotation.
I'm wondering if specifying the start level in SCDL is crossing
semantics with eager init...
As background, one thing I was planning on proposing to the spec was
moving eager init off of @Init and onto @Scope for couple of reasons.
First, eagerness is associated with the scope, not an initializer
callback, IMO. The second reason is that it avoids a problem I've
been noticing lately where I want to eager init something but I don't
need an initializer callback, and I am forced to add an empty method
just to get the component to be instantiated eagerly. Couple that
with constructor-based injection, and I think it is better to but
things on @Scope.
What if we said eager init is a component type concept and is true or
false (specified on @Scope)? Then, run level is the SCDL
configuration of eager init. So, a component would be eager
initialized based on the component type info and would be done so in
the order specified by the SCDL runlevel attribute. If no runlevel
attribute were present, we would default it to some level (maybe 100).
Also, I think we should have a default runlevel attribute on
composites as well that applies to all children. This may be implicit
in the above since composites are just components.
Jim
Seem reasonable?
--
Jeremy
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