Hi all! What is the difference between Job and Sup...

# coroutines

[ahulyk]

Hi all!
What is the difference between Job and SupervisorJob in case of Exception Handling?

class Presenter() : CoroutineScope {
        private val job = Job()

        override val coroutineContext: CoroutineContext
            get() = job + Dispatchers.Main

        override fun onDestroy() {
            job.cancel()
        }

        fun loadData() {
            launch {
                try {
                    //loadData().async()
                } catch (e: Exception) {
                    //handle exception
                }
            }

        }
    }

class Presenter() : CoroutineScope {
        private val job = SupervisorJob()

        override val coroutineContext: CoroutineContext
            get() = job + Dispatchers.Main

        override fun onDestroy() {
            job.cancel()
        }

        fun loadData() {
            launch {
                try {
                    //loadData().async()
                } catch (e: Exception) {
                    //handle exception
                }
            }

        }
    }

[gildor]

Did you read docs of SupervisorJob?

[ahulyk]

Yes,
looks like second example is the way to go in most cases.

[ahulyk]

I found exactly my case - https://github.com/Kotlin/kotlinx.coroutines/issues/996

[gildor]

What is the actual difference between SupervisorJob() and CoroutineScope constructor?

This question doesn’t make make sense, Job and Scope are different things

[gildor]

In your case difference caused by different work of Job and SupervisorJob (and by default scope uses Job)

[gildor]

What is not clear for you? Why Job works like that? Or why do you have this exception?

[ahulyk]

@gildor The only part that is still unclear for me is why the following solution should work?

use the following shortcut via CoroutineScope constructor:

class UserViewModel: ViewModel, CoroutineScope by CoroutineScope(Dispatchers.Default) {
    override fun onCleared() {
        super.onCleared()
        cancel()
    }
}

The working solution is to create new Job(), after exception is caught:

CoroutineExceptionHandler { _, throwable ->
        //onError(throwable)
        job = Job()
    }

[gildor]

job = Job() - this looks wrong

[gildor]

why the following solution should work?

Could you elaborate, what exactly means “should work”, does it work for you?

[gildor]

It’s pretty clear in your original example

[gildor]

but I don’t understand what you want to do in your last message

[ahulyk]

The question is related to Roman Elizarov answer:
https://github.com/Kotlin/kotlinx.coroutines/issues/996#issuecomment-468890079
SupervisorJob() works great but the second solution does not.

[gildor]

But this not related to CoroutineExceptionHandler

[ahulyk]

ok - now i got it 🙂

[ahulyk]

thanks!

[gildor]

or use the following shortcut via CoroutineScope constructor:

I actually not sure what Romain means by this, this is exactly the same as version above, just more concise

[gildor]

but SupervisorJob is definitely related

[ahulyk]

Yeap, SupervisorJob works great!