I'm new to Koin and ran across something that was ...

# koin

[humblehacker]

I'm new to Koin and ran across something that was unexpected and I'd like to know if I'm either understanding it wrong, or doing it wrong.

I've got a dependency declared as factory { Service() }, and I'm attempting to use it in a class as a property declared as val service: Service by inject(). It works, but it seems that every time I reference that property in my class, Koin creates a new instance. Is that how it's supposed to work? I expected it to construct the Service lazily, but after that I'd get the same instance until the parent class is destroyed. Changing by inject() to = get() gets me the behavior I want, but I really want to know why by inject() isn't working as I expect.

[Sebastian Schuberth]

Yes, that's intended behavior if you use factory {}. If you don't want a new instance to be created on each injection, use single {} instead.

[humblehacker]

Thanks for your reply @Sebastian Schuberth. Can you define "each injection"? I would expect that for a given class instance, an injected property would be injected only once - which happens when I use = get() but not with by inject(). It seems quite odd that every time I reference a property declared by inject(), the old instance is released and a new one created.

single {} would give me the same instance every time I create a new instance of the parent class, which is not what I want.

[Sebastian Schuberth]

I'm quite new to Koin myself and by far no expert, @humblehacker. I'm basically just repeating my understanding of https://insert-koin.io/docs/reference/koin-core/definitions#defining-a-factory.

[humblehacker]

I figured it out. My expectation was correct, my implementation was not.

Turned out to be a classic race condition. by inject() under the hood uses Lazy with LazyThreadSafeMode.NONE as default (unlike by lazy() which defaults to LazyThreadSafeMode.SYNCHRONIZED), and since I was accessing my property from multiple threads (via suspendCancellableCoroutine), multiple instances were created before Lazy had a chance to store one.

Solution is to change my property declaration like so:

val service: Service by inject(mode = LazyThreadSafetyMode.SYNCHRONIZED)

or take other steps to ensure thread-safe access to that property.