What's the purpose of the `Flow.cancellable` operator ? What kind of use case does it solve ?

# coroutines

[tseisel]

What's the purpose of the Flow.cancellable operator ? What kind of use case does it solve ?

[louiscad]

I think it's for when you have a flow that is made completely out of non cancellable functions but you want it to be cancellable on element emission.

Am I right @elizarov?

[elizarov]

Right

[octylFractal]

https://gist.github.com/octylFractal/9cd8b2cd0c71c123d657acde8fef3d31 is a simple example

[louiscad]

That example is ready to paste in the editor on kotl.in or play.kotlin for you to try @tseisel

[tseisel]

I see, this checks for cancellation on each emit and propagate it when applicable, which is not performed otherwise for performance reasons.
Does this apply for thread-blocking code as well ? Thread.sleep show a different behavior

[octylFractal]

no, unless you wrap it in runInterruptible -- cancellation must be picked up by checking isActive, which is impossible for anything that isn't depending on the coroutines library (this means that suspend functions defined in stdlib also are not cancellable)

[octylFractal]

runInterruptible registers a handler on the appropriate Job that calls Thread.interrupt() on cancellation

[louiscad]

@octylFractal Where does runInterruptible come from?

[octylFractal]

coroutines library? https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/run-interruptible.html

[louiscad]

Ah, I had to update kotllinx.coroutines in the project I'm working on (how ironic since it's a project to update libraries!), TIL this exists, great stuff for interop, thank you 👍