On Jul 14, 2006, at 1:13 PM, Meeraj Kunnumpurath wrote:
First, eagerness is associated with the scope, not an initializer
callback, IMO.
Jim, would this mean there would be another annotation for
initialization callbacks?
I think it would just be @Init, but with no attributes
Also, what are the implications of start order on component
dependencies
and wirings?
That's a good question. I think dependencies override start order
such that when we initialize a component, we perform a depth-first
traversal of dependencies, instantiating them regardless of start
level. Are you thinking of something that may cause complications
with this approach?
Jim
Many thanks
Meeraj
-----Original Message-----
From: Jim Marino [mailto:[EMAIL PROTECTED]
Sent: 14 July 2006 21:05
To: [email protected]
Subject: Re: Component start order
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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