Is there anything particularly special with vmScope.coroutineContext? When I use CoroutineScope(job ...

# coroutines

[Arun Joseph]

Is there anything particularly special with vmScope.coroutineContext?
When I use CoroutineScope(job + vmScope.coroutineContext) to launch coroutine and use job.cancel() it doesn't cancel the coroutine.
This is an example https://pl.kotl.in/e0WxVRCBt which is able to cancel with another context in place of vmScope.coroutineContext

[bezrukov]

vmScope.coroutineContext have a Job too, and when you're doing
CoroutineContext+CoroutineContext is not symmetric, so if both contexts have an element of the same type (in your example it's Job) the one from the second context wins. So you need to use

vmScope.coroutineContext + job

to get it working.

[bezrukov]

But note, that now once you cancel vmScope, anything launched with job won't be canceled. To make it working you need to define Job's parent<->child relation:

val job = Job(vmScope.coroutineContext.job) // now new Job is a child of job from vmScope
val newScope = CoroutineScope(vmScope.coroutineContext + job)

[Arun Joseph]

Let me try and check both scenarios to see the difference.

[Arun Joseph]

I tested vmScope.coroutineContext + job first, found that job wasn't cancelled when vmScope is cleared.
Then with

val job = Job(vmScope.coroutineContext.job) // now new Job is a child of job from vmScope
val newScope = CoroutineScope(vmScope.coroutineContext + job)

the job is cancelled on job.cancel and when vmScope is cleared.
Thanks!

[Arun Joseph]

I see that with the new approach, this also works and correct?

val job = Job(vmScope.coroutineContext.job) // now new Job is a child of job from vmScope
val newScope = CoroutineScope(job)

[bezrukov]

kinda, you will loose other elements from the original context (typically Dispatcher, but also maybe CoroutineExceptionHandler/CoroutineName/ThreadLocal element etc)