Sorry for more one question but I am trying unders...

# juul-libraries

[Francis Mariano]

Sorry for more one question but I am trying understand more about coroutine and kable is a great use case.

private val job = SupervisorJob(parentCoroutineContext.job) 
private val scope = CoroutineScope(parentCoroutineContext + job)
private val connectionScope = CoroutineScope(scope.coroutineContext + Job(scope.coroutineContext[Job]))

Here is what I understood about the code quoted above:
scope inherits parent's context but with new job . That job is a SupervisorJob so if any child of scope fails or is cancelled it manage each one separately (if one child fail or cancel the others child continue working and the parent also is not cancelled)
job inherits parent's job. If parent is cancelled all the child also is cancelled.

Here is what I did not understand:
connectionScope inherits context and job of scope . Are they the same????

[travis]

One way to look at it is:

The plus operator for coroutine context properties replaces the previous element.

So, in your example, connectionScope will have all the same CoroutineContext elements except its Job will have been overwritten by the Job(parentJob) that you did. It will essentially be a copy of scope but with its parent being scope. Otherwise anything that was configured previously on that CoroutineContext such as exception handlers or dispatches, will be the same on the two scopes.

This is a great article on the topic: https://proandroiddev.com/demystifying-coroutinecontext-1ce5b68407ad

[travis]

The Job is what is used for cancellation, so your connectionScope will have all the same dispatchers as scope, but you can now cancel it and it won't cancel scope (because they have different `Job`s).

[travis]

Because you create connectionScope w/ a Job that is a child of `scope`'s Job, if you cancel scope then it will cancel its `Job`'s children (which means connectionScope will also cancel in that case).

[Francis Mariano]

I got the sample code from Kable library 😄. I understand now.

The Job is what is used for cancellation, so your connectionScope will have all the same dispatchers as scope, but you can now cancel it and it won't cancel scope (because they have different Jobs).

But if I cancel connectionScope with exception different of CancellationException so scope is also cancelled, right???

[Francis Mariano]

scope does not have parentJob, so only scope can cancel itself, ok?

[travis]

If you're referring to Kable, the scope is configured with a parent:

https://github.com/JuulLabs/kable/blob/main/core/src/androidMain/kotlin/Peripheral.kt#L144

The parent scope is the receiver of the peripheral extension function.

So, whenever you create a peripheral, you decide what you want the parent CoroutineScope to be. If you cancel the scope used as the receiver of the peripheral extension function then the `Peripheral`'s internal scope will be cancelled.