So, as a library author, if you choose to create s...

# coroutines

[groostav]

So, as a library author, if you choose to create some type MyWorkingThing: kotlinx.coroutines.Job, what kinds of things should you do with cancellation? In my case, MyWorkingThing acquires a resource that I would like to synchronize on the disposal of before letting the job hit the Compelted state. The Cancelling state seems to reflect this well: if you hit cancel() on a job, it goes cancelling while it attempts to clean up its resources.

The problem is cleaning up those resources is itself a long-running operation, and I cant suspend something while its being cancelled because, well, its being cancelled. Should I just block? Should I just document MyWorkingThing with some docs to the effect of:

hey, if you cancel a MyWorkingThing its going to launch some teardown jobs in global scope.

[louiscad]

Here's what you can do, but just make sure cancellation doesn't imply a possible deadlock.

try {
    doSomethingCancellable()
} finally {
    withContext(NonCancellable) {
        cancelYourStuff()
    }
}

[groostav]

the docs for invokeOnCompletion alarm me a little:

Note: This function is a part of internal machinery that supports parent-child hierarchies and allows for implementation of suspending functions that wait on the Job's state. This function should not be used in general application code. Implementations of CompletionHandler must be fast and lock-free.

I'm actually overriding the onCancellation handler for AbstractCoroutine, but I dont think that buys me anything.

I've since updated my tests to reflect that suspend fun kill() will stop the task and synchronize on its release of resources, where fun cancel() will simply start the process of cleaning up resources and return immediately.

[louiscad]

@groostav That applies to CompletionHandler which is a regular function, but not to the finally block that is still in a continuation and can attempt to suspend (though only possible with NonCancellable 👍, or shady hacks with scopes that I don't recommend 👎).