Hi!, all... which is the difference between GlobalScope.async and CoroutineScope(context).launch?? ...

# coroutines

[Laura de la rosa]

Hi!, all... which is the difference between GlobalScope.async and CoroutineScope(context).launch?? can someone explain me

[Dominaezzz]

There are 4 differences here.

[Dominaezzz]

launch vs async.

[Dominaezzz]

GlobalScope vs CoroutineScope(context)

[Dominaezzz]

The missing differences are in that hidden context.

[Laura de la rosa]

I need the difference between this GlobalScope vs CoroutineScope(context)

[Dominaezzz]

The latter adds an extra allocation. Behaviour is about the same.

[Dominaezzz]

I can give a more in-depth explanation, if I know what is in context.

[Laura de la rosa]

ok, I need to access to the contacts of the cellphone, I need this operation async, if I try using CoroutineScope(context) my app blocks, if I try with GlobalScope.launch I get what I want. but Im worjing in kotlin multiplatform so I need this working for android and ios... in android always take the main context by default, but in ios I need to specify it. so I don't know if GlobalScope.launch is gonna work for ios

[streetsofboston]

For `GlobalScope`: It has an ‘empty’ context, ie. no fixed dispatcher (launches, asyncs use the Dispatchers.Unconfined, unless you switch it by using withContext, etc), and it has no Job (ie. You can’t cancel a GlobalScope, for example)

[Laura de la rosa]

because I never specify a context for ios

[streetsofboston]

When doing val scope = CoroutineScope(), it will add a Job() to its coroutineContext, by default

[Dominaezzz]

Which won't matter if you don't keep a reference to it.

[streetsofboston]

Yup, true.
But you may want to provide a SupervisorJob() if needed. But the default providing of Job() is a good default.
But using the factory method CoroutineScope(...), it always will have a Job, which means it is cancelable, whereas GlobalScope isn’t

[Laura de la rosa]

so I should use a val scope = CoroutineScope(context)

[streetsofboston]

If you are planning on calling scope.cancel() at some point, yes.

[streetsofboston]

If you launches and asyncs are truly global and should never be canceled (unless you entire process aborts), then use GlobalScope.

[Laura de la rosa]

and if I dont want a scope.cancel()

[Laura de la rosa]

I can use GlobalScope

[Laura de la rosa]

thank you very much ❤️

[streetsofboston]

Looks like it.
Be sure to provide the proper dispatcher to your launches and asyncs, since GlobalScope uses the Unconfined dispatcher, which may surprise you here and there 🙂

[Laura de la rosa]

how I provide a dispatcher in GlobalScope?

[streetsofboston]

GlobalScope.launch(dispatcher) { … }

[streetsofboston]

or

GlobalScope.launch {
    withContext(dispatcher) {
        ... 
    }
}

[Laura de la rosa]

thank you very much! you both are the best ❤️

[streetsofboston]

I must admit, to avoid providing the dispatcher when calling launch and such, instead of GlobalScope, I use CoroutineScope(dispatcher) …. I just never call ‘cancel()’ on it 🙂

[Laura de la rosa]

why CoroutineScope(dispatcher) blocks me the app and GlobalScope no?

[streetsofboston]

Not sure what you mean with ‘blocks me the app’.

[Laura de la rosa]

is like CoroutineScope(dispatcher) no has a async behaviour

[streetsofboston]

You said you use it on iOS?

[Dominaezzz]

Oh that's why.

[streetsofboston]

https://medium.com/quick-code/kotlin-native-ios-a1a73d7390fe

[streetsofboston]

Google “kotlin ios coroutinescope” and you’ll find quite a few articles/post/issues with this (and hopefully some solutions)

[Zach Klippenstein (he/him) [MOD]]

@basher just gave a great talk on using coroutines in K/N to do background work – not sure if the slides are up anywhere

[basher]

Slides are up! No video yet: https://twitter.com/benasher44/status/1166892473303494657?s=21