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Correction:
On 30. 09. 20 13:42, Ladislav Thon
wrote:
Clearly the idea is to replace CDI extensions
OK, I got carried away a bit too much. Please disregard the
"replace" word -- at this point, it's way premature. Let's say
"find an alternative". What it really becomes in the end is hard
to know at this point.
Sorry, and thanks for understanding.
LT
with a mechanism that is similarly powerful, caters to similar
use cases, but removes an important architectural constraint
(the need for everything to run in a single JVM).
As a developer, I want to use the CDI extension
to:
Providing its own beans, interceptors and decorators
to the container
The `@Discovery` phase has a method to add arbitrary classes to
the "application". If such class doesn't have a bean defining
annotation etc., you can add those annotation in the
`@Enhancement` phase.
Injecting dependencies into its own objects using the
dependency injection service
Sorry, I'm not sure what this means.
Is this about extension-contributed classes being treated as
application classes, i.e. can have dependencies injected and
themselves being injected, can declare observers, etc. etc.? If
so, then sure, I'd say that's a given.
Or is this about being able to access the extension instance at
application runtime? That would be a no-no I'm afraid. The
instance is potentially long gone when the application starts.
The class is potentially a different class (loaded by a
different classloader in a different JVM).
Providing a context implementation for a custom scope
The `@Discovery` phase has a method to register custom context
class. If the class doesn't have all the necessary metadata
(such as the scope annotation), the API also has methods to set
those.
Augmenting or overriding the annotation-based metadata
with metadata from some other source
The `@Enhancement` phase is all about this.
There's also an API to add synthetic beans and observers
(`@Synthesis`), and an API for validating the application and
preventing successful build/deployment (`@Validation`). To sum
up, the most important use cases for CDI extensions, as far as I
can tell, are covered.
LT, can you double check whether this is the use case
your PR is for? It will be very appreciated if you can put
some code snippets to demonstrate how to achieve some of the
use cases.
OK, let me try.
Registering a custom context:
public class MyContext implements AlterableContext { ... }
public class MyExtension {
@Discovery
public void customContext(Contexts contexts) {
contexts.add().implementation(MyContext.class);
}
}
Contributing a bean to the application:
@ApplicationScoped
public class MyBean { ... }
public class MyExtension {
@Discovery
public void customBean(AppArchiveBuilder app) {
app.add(MyBean.class);
}
}
Contributing a non-bean class to the application and making it
a bean:
public class MyBean { ... }
public class MyExtension {
@Discovery
public void customClass(AppArchiveBuilder app) {
app.add(MyBean.class);
}
@Enhancement
public void makeItABean(ClassConfig<MyBean> bean) {
bean.addAnnotation(ApplicationScoped.class);
}
}
Vetoing a bean:
public class MyExtension {
@Enhancement
public void vetoABean(ClassConfig<SomeBean> bean) {
bean.addAnnotation(Vetoed.class);
}
}
Makes sense? I know these are toy examples, but should give you
an idea.
LT
If you can't deal with some of the use cases listed
above, we can discuss here on whether we should reduce the
scope or we can suggest some alternative solutions.
Thanks,
Emily
On Wed, Sep 30, 2020 at 9:41
AM Ladislav Thon <lthon@xxxxxxxxxx> wrote:
Yes. With (truly!!) all respect
to Antoine, it's a bit all over the
place and not a list of use cases or
goals.
Can we just put down here, in
simple bullet point formats, what at
least the goals of this effort are?
I don't mean to suggest this is a
trivial exercise, because it is not,
and Emily certainly tried to get it
rolling before (mostly
unsuccessfully) with issue #425 (https://github.com/eclipse-ee4j/cdi/issues/425;
and I applaud her attempt to start
with the use cases). But let's try
again, here, publicly, on this list.
For the record, I'm definitely
aware of {handwave} build time
{handwave} no reflection {handwave}
but I'm quite sure we can do better
than that as a group. Here is an
incomplete sketch of one example of
the sort of thing I had in mind.
Meta-goal: disrupt the
specification as little as humanly
possible (true of all specifications
everywhere that are this old)
Goal: permit a CDI SeContainer to
run a precomputed set of beans
without having to run portable
extensions
Why: certain products create
their beans at build time/ahead of
time: we want them to be part of the
CDI fold as well
Hindrance: the
SeContainerInitializer/portable
extension APIs, even with something
like
SeContainerInitializer.disableDiscovery().addExtension(new
Extension() { /* add beans here
however they are generated/created
*/ }) is insufficient because of X,
Y and Z
Hindrance: all (not just some)
portable extensions must be
available at runtime via
BeanManager#getExtension()
…etc. and so on. I can see the
germs of something like this lurking
in your posts and others' and in
Antoine's blog article and elsewhere
but I think it is necessary that we
have small, traceable, actionable
goals spelled out here before we try
to solve them.
So I think we have explained the why quite
a bit, and importantly we are talking about
fundamental compatibility differences
(two-phase multi-VM execution vs one phase),
so you are already at the point of having to
start anew. It’s not something that a simple
API tweak here and there is going to solve.
Totally agree. I'd highlight what you put into parens
:-) I have never considered it a use case, or anything
worth extra mentioning, which in hindsight is an obivous
mistake, so let me try to phrase it concretely.
Goal: modify the specification and the APIs to no
longer assume that everything happens in a single JVM.
It should be possible for a big part of the "application
initialization lifecycle", including extensions, to run
in another JVM, to "pre-wire" the application statically
and enable significant performance gains during actual
application startup.
(I understand this might not necessarily be a SMART
goal. Sorry about that, I'm a simple man and prefer
debating concrete ideas rather than abstract
methodologies.)
Just a small clarification that I am specifically
referring to portable extensions (#434) and the
proposal (#451) which is the subject of this thread.
This is the area that requires a reboot, to cover the
same extension author use cases.
The other areas of CDI are less of a problem, each
of those items will have their own issue against them
(which might involve small spec wording changes).
Some of them might be future decision points (should
lite include X yes/no?) However, the hardest part of a
potential CDI-Lite is solving the portable extension
problem, so IMO it makes sense to tackle this area
first. FWIW we new this would tough, so we first
proposed just leaving this aspect to venders, but a
number of commenters really wanted to see work on a
new SPI. So here we go :)