Can somebody help me understand why I m getting kotlinx coro

Question

Can somebody help me understand why I m getting kotlinx coroutines JobCancellationException Parent job is Completed when I try to start my web service in my view model I m trying to delay the connection until after I have an auth token so that the connect will be successful

Adam Powell · Answer

Catching `Throwable` and not rethrowing is likely breaking cancellation

Adam Powell · Answer

This code also looks like it can and will start multiple concurrent connection attempts which is unlikely to be what you want

Trey · Answer

That is correct I would only want to connect if not connected I would add a check to skip if already connected The block catching the exception shouldn t cause the JobCancellationException right

Adam Powell · Answer

A cancellation exception is normal in viewModelScope ViewModel clear cancels the scope s job

Adam Powell · Answer

It s the natural mechanism used to stop viewModelScope work

Adam Powell · Answer

But by catching it you re preventing that graceful teardown so your flow doesn t stop collecting

Trey · Answer

Gotcha I can re throw Right now I m getting the cancellation exception on line 10 when trying to connect to the web service What would be the correct way to launch another coroutine based on the value returned from a flow

julian · Answer

How come you re using `async` when you do nothing with the `Deferred` returned Also if you re interested in just one value from `userState` and it s a `Flow` why not just `take 1 ` instead of wrapping in `collect` Also as is `viewModelScope launch` and `viewModelScope async` will run concurrently Wouldn t you prefer the inner coroutine to be a child of the outer one That way cancelling the job of the outer one would automatically cascade down to cancel the inner one

Trey · Answer

There was other initialization stuff in the init block that I removed Without async the other stuff would be blocked I could move that other stuff out and launch that separately I m interested in this for when the user logs out back in too so I want to continue collecting Any idea why I m getting the parent job completed exception I ve overrode onCleared in my view model and it isn t called I m not sure why the job would be completed

julian · Answer

The only parent job evident from what you ve shared is the job of the `viewModelScope` itself which is a `SupervisorJob` I don t see how that could have completed if `onCleared` was never called Are there any other parent child job relationships in play that we can t see from the code given The exception suggests that you re trying to do something with a job whose parent has completed Question is which parent job is that

julian · Answer

Are you using a custom `viewModelScope` that doesn t use a `SupervisorJob`

Trey · Answer

It is just the regular viewModelScope One strange thing that I noticed is that if I switch the uiState to use a SharedFlow instead of a StateFlow this code works The problem with using a SharedFlow is that updating the state for logout doesn t work It just suspends and never updates the ui state

julian · Answer

How many times is `collect` called before the exception occurs

Trey · Answer

Twice Login logout then logging back in causes the exception So on the third UserState with isLoggedIn set to true

julian · Answer

Is it possible that `webService` is still connecting when `disconnect` is called If so how does `webService` behave in this situation I assume `connect` and `disconnect` are not `suspend` functions Is that right

Trey · Answer

The web service is using HttpClient from ktor It loops forever in the DefaultClientWebSocketSession when you open the request until close is called on the HttpClient instance I think that closing that client is related somehow