Hi. I'm relatively new to Coroutines. Is it okey to use `GlobalScope.launch { }` to run an infinite ...

# coroutines

[Jérôme Gully]

Hi. I'm relatively new to Coroutines. Is it okey to use GlobalScope.launch { } to run an infinite while to draw on canvas (Android SurfaceView) or it is a better solution ?

Sans titre

[zak.taccardi]

no

[zak.taccardi]

Views have a lifecycle

[zak.taccardi]

UI has a lifecycle (activities, fragments, etc)

[zak.taccardi]

and that lifecycle is not global

[Jérôme Gully]

Ok, so I must run the coroutine attached to the lifecycle of the view.

[zak.taccardi]

so if you use global scope, your coroutine will continue to run when the view or activity is destroyed

[Jérôme Gully]

Ok, and stop running only when the app is destroyed, is that ?

[zak.taccardi]

for example, if it were activity:

lateinit var onCreateScope: CoroutineScope
fun onCreate(){
  onCreateScope = CoroutineScope(Dispatchers.Main)  
}

fun onDestroy() {
  onCreateScope.cancel()
}

[Jérôme Gully]

I found an exemple code (https://github.com/elye/demo_android_surfaceview_vs_view/blob/7ffb8481788b2b1eadd0da58536b92db1293f229/app/src/main/java/com/elyeproj/surfaceviewexplore/SlowSurfaceView.kt#L39) and it's seems that it's for an old version of couroutines, without notion of scopes

[Jérôme Gully]

So I don't need a job propertie and I can directly call surfaceViewScope.cancel() in surfaceDestroyed(), if I'm right 🙂

[zak.taccardi]

correct

[zak.taccardi]

that’s what is awesome about scopes 🙂

[zak.taccardi]

you define lifecycle (the scoping) first, then you can launch coroutines!

[Jérôme Gully]

It's still a bit unatural to have to define it explicitly, but I understand the concept, thanks for the help !

[Jérôme Gully]

Lot of time, if you use LifeCycle librabry, I think you can attached coroutine to the lifecycleowner

[Jérôme Gully]

Because my needed was to have a background worker for the SurfaceView, I was been able to define directly my propertie on declaration with private val surfaceViewScope = CoroutineScope(Dispatchers.Default), I guess it's right 😬

[zak.taccardi]

just make sure you switch to the main thread for main specific code

[Jérôme Gully]

Like it, must spend more time on Coroutines

[zak.taccardi]

also, realize that Dispatchers.Default is a thread pool, so if you launch more than one coroutine you lose thread safety (any code confined to a single coroutine is thread safe, even if it runs across multiple threads)

[Jérôme Gully]

Ok thanks, in my case it's Ok I guess.

[Jérôme Gully]

It's the same for the IO dispatcher ?

[zak.taccardi]

yes, but the IO dispatcher is for blocking calls that don’t do any work while they block a thread