CoroutineScope cancellation requires a Job

[ZakTaccardi]

I expected a CoroutineScope to be cancellable on it's own. But a Job must be specified for a CoroutineScope to be cancelled. This seems a bit odd and error-prone.

Example

The following fails with IllegalStateException: Scope should no longer be active:

val scope = CoroutineScope(dispatcher)
check(scope.isActive) { "Scope should be active" }

scope.coroutineContext.cancel()

check(!scope.coroutineContext.isActive) { "Dispatcher should no longer be active" }
check(!scope.isActive) { "Scope should no longer be active" } // fails here

But if you cancel via a job, no problems:

val job = Job()
val scope = CoroutineScope(dispatcher + job)
check(scope.isActive) { "Scope should be active" }

job.cancel()

check(!scope.coroutineContext.isActive) { "Dispatcher should no longer be active" }
check(!scope.isActive) { "Scope should no longer be active" }

[fvasco]

It seems a bug

isActive is a shortcut for coroutineContext.isActive

https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental/is-active.html

[elizarov]

This is not a bug. It is so by design. The cancellation is supported via Job.

[elizarov]

To help with this function and make it more use-friendly, we'll change it to throw an exception if the context does not contain a Job.

[fvasco]

Should the documentation fixed?

isActive and coroutineContext.isActive have different behaviour, despite the documentation.

[elizarov]

Nope. That was bad idea. We'll create Job() if it is missing. This way, we'll need no change to .isActive documentation either