RxSwift Observable race condition

Question

I have an object created from flatMap ing an observable.

private lazy var childObj: chilView? = {

    let keychainStore = Realm().getStore()

    let selectedElementID = keychainStore.elementID
        .asObservable()
        .distinctUntilChanged {$0 == $1}
        .flatMap({ (elementID) -> Observable<Element?> in
            guard let elementID = elementID else {
                return Observable.error(Errors.InvalidElementID)
            }

            return Observable.create { observer in
                let elementStream: Observable<Result<Element>> = keychainStore.getObservable(id: elementID)
                elementStream.subscribe(onNext: { (result) in
                    switch result {
                    case .success(let element):
                        observer.onNext(element)
                    default: break
                    }
                })
                .disposed(by: self.disposeBag)

                return Disposables.create()
            }
        })

    return self.createChildObject(with: selectedElementID)
}()

The selectedElement is of type flatMap observable. createChildObject(with:) is called even before observer.onNext(element) is executed. How do I fix this?

Answer 1

I am not sure I completely understand your problem from the description but here are some thoughts:

It's not a race condition. Your selectedElementID chain and the flatMap code within it will not be executed before you subscribe to the selectedElementID . So I guess you subscribe to the selectedElementID somewhere within createChildObject method and obviously get the createChildObject code executed before the selectedElementID chain.

Depending on how keychainStore rx calls are designed and how you subscribe to selectedElementID observable you might get a race condition but I am not sure that the using RxSwift is a good decision in this case. Try making your chains more atomic.