Another thing that troubles me why `SupervisorJob` is design kotlinlang #coroutines

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Title

m

marcinmoskala

07/17/2021, 8:25 AM

Another thing that troubles me - why

SupervisorJob

is designed in this way, that it needs to be a part of scope, and does not work as a simple context passed as an argument?

fun main(): Unit = runBlocking(SupervisorJob()) {
    launch {
        delay(100)
        throw Error()
    }
    launch {
        delay(200)
        print("Done")
    }
}
// Just Error

fun main(): Unit = runBlocking {
    with(CoroutineScope(coroutineContext + SupervisorJob())) {
        launch {
            delay(100)
            throw Error()
        }
        val job = launch {
            delay(200)
            print("Done")
        }
        job.join()
    }
}
// Error...
// Done

e

ephemient

07/17/2021, 5:51 PM

supervisorScope {

👍🏻 1

it's similar to

withContext(SupervisorJob())

but works to keep structured concurrency

note that what you have there has another danger: if you create a new coroutine scope and don't keep any references to it (or something in it) it may be garbage collected and stop running

m

marcinmoskala

07/18/2021, 8:32 AM

I found the answer myself - the first case does not work, because those launches are child of a child of a

SupervisorJob

.

runBlocking

makes a child job, and

launch

also makes a child based on the

runBlocking

job.

SupervisorJob

gives a special behaviour only for its children, not children of its children.

This is error resilient:

fun main(): Unit = runBlocking {
    val s = SupervisorJob()
    launch(s) {
        delay(100)
        throw Error()
    }
    launch(s) {
        delay(200)
        print("Done")
    }
    delay(300)
    s.complete()
    s.join()
}
// Error
// Done

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