Avoid locking the lazy provider when the value is cached

[SentryMan]

• no longer locks the thread for every lazy provider request
• change ProviderPromise to retrieve the provider from the bean map when get is called

[rob-bygrave]

change ProviderPromise to retrieve the provider from the bean map when get is called

Why do that? This is changing the semantics?

[SentryMan]

Why do that?

I'm getting null pointer exceptions when trying to use a provider within a Beanscope.

[SentryMan]

due to certain peculiarities with re-authenticating mongo I'm trying to register a Provider that will rotate the credentials and give the updated MongoCollection. It seems though that when I call get after wiring this happens

Cannot invoke "jakarta.inject.Provider.get()" because "this.provider" is null

Example Code:

class MyRepoImpl {

  final Provider<MongoCollection> cProv;

  MongoCollection coll;

  RepoImpl(Provider<MongoCollection> cProv){
    this.cProv = cProv;
    coll = cProv.get(); // dies here
  }
  
  getRotatedMongo() {
    coll = cProv.get();
  }

  someOperation() {
 
    //if some Auth Error
   getRotatedMongo()
  }
}

[rbygrave]

Well ok but I think that means we need 2 separate PRs. We need to document the NPE bug as a bug with ideally a stack trace that folks might be able to find etc. Plus we need the history as people read it via the PR titles to reasonably reflect the change (and so currently the title does not reflect anything about a NPE bug).

So yeah, I think we need to split this into 2 PRs for those reasons.

[rbygrave]

It seems though that when I call get after wiring this happens

Technically the get is being called during wiring. That is the constructor is called during wiring (and wiring has not completed yet and this is why the NPE). I think the expectation would have been to use a @PostConstuct here - Hmm.

[rbygrave]

My thought is that instead of Provider<MongoCollection> a Supplier<MongoCollection> could have been used here, a bit like: https://github.com/avaje/avaje-inject/pull/521/files

In this way the Supplier.get() method can be called inside the constructor (during wiring).