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#coroutines
Title
# coroutines
m
Marko Mitic
05/08/2019, 12:28 PMIs there a way to check whether coroutine (scope) was canceled from a suspend function (that function not being extension of the scope)?
a
altavir
05/08/2019, 12:29 PMisActivem
Marko Mitic
05/08/2019, 12:30 PMisActive isn't visible in suspend fun, it's part of CoroutineScope
this is what I'd like to do
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fun CoroutineScope.launchSomething(){
launch {
ComplexClassWithState().run()
}
}
class ComplexClassWithState {
suspend fun run(){
while (isActive){
//do stuff
}
}
}a
altavir
05/08/2019, 12:34 PMIf you do not have the scope, I would not recommend it since you can't guarantee, how the function will be called. You can add empty suspension points like
delay(0)m
Marko Mitic
05/08/2019, 12:35 PMthis is what I'm doing right now
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fun CoroutineScope.launchSomething(){
launch {
ComplexClassWithState().run(this)
}
}
class ComplexClassWithState {
suspend fun run(scope: CoroutineScope){
while (scope.isActive){
//do stuff
}
}
}Looking at the code, doesn't looks like
delay(0) Copy code
public suspend fun delay(timeMillis: Long) {
if (timeMillis <= 0) return // don't delay
...
}a
altavir
05/08/2019, 12:44 PMit does not. It just creates a suspension point. If the coroutine is canceled, suspension point will throw an exception. Any suspension point will do.
I think that there was a function, that just creates a suspension point and does not do anything else... Just do not remember the name
m
Marko Mitic
05/08/2019, 12:56 PMthis is probably an overkill, right?
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val isActive = runCatching {
suspendCoroutine<Boolean> { continuation ->
continuation.resumeWith(Result.success(continuation.context.isActive))
}
}.getOrDefault(false)a
altavir
05/08/2019, 12:57 PMprobably. I do not recommend use naked coroutine primitives unless you really do understand what are you doing. I do not.
g
gergo
05/08/2019, 1:26 PMwrapping the suspend function's body into a coroutineScope doesnt resolve this?
a
altavir
05/08/2019, 1:28 PMNo, it does not. You need to create a suspension point, otherwise kotlin would not know, where it can safely terminate computation.
g
gergo
05/08/2019, 1:32 PMi meant like coroutineScope{ while(isActive) {} }. but i guess you are right adding yield() into the function resolves this.
thank you!
a
altavir
05/08/2019, 1:32 PMwell, yes, you can. But it changes semantics a bit.
And no, if you just add scope without creating suspension point inside the cycle, it still won't work.
g
gergo
05/08/2019, 1:36 PMi am not sure why it wouldn't work with scope, would you be kind enough to explain?
a
altavir
05/08/2019, 1:38 PMIf there are no suspension points in the cycle, then it just won't stop until it reaches the end of the scope. You need some place to throw an exception, you can't do it in a random point of the program.
g
gergo
05/08/2019, 1:40 PMthe isActive would change even if job of the outer scope were canceled, or it wouldnt be?
a
altavir
05/08/2019, 1:41 PMisActive would work. It explicitly checks the coroutine state. And yes, it will in general show the state of outer scope as well. You need either
isActiveg
gergo
05/08/2019, 1:43 PMokay, so if i get it correctly you suggest something like
while(true) { yield(); /* do stuff */ }coroutineScope{ while(isActive) { /* do stuff */ } }a
altavir
05/08/2019, 1:44 PMWell, I think both ways are good. The one with coroutineScope just has a little bit different meaning.
g
gergo
05/08/2019, 1:45 PMokay, i think i need to read a bit more about this. thank you for your help!
a
altavir
05/08/2019, 1:46 PMBasically it changes how you work with exceptions. yield will drop the exception right where you got it.
coroutineScopeisActive👍 1
g
gildor
05/08/2019, 1:53 PMisActive isn't visible in suspend fun, it's part of CoroutineScopeisActive is extension property which isavailable in any suspend function, not only on scope, it just search for Job in coroutine context
a
altavir
05/08/2019, 1:55 PMIt is not extension if you do not have scope. It is internal API. I am not sure, it could be used outside inlines. Never tried.
g
gildor
05/08/2019, 1:56 PMYou shouldn't use coroutineScope builder function for this, it doesn't make sense, just use isActive directly
a
altavir
05/08/2019, 1:57 PMI just tried. It is part of
JobMaybe I tried in project with old coroutines though...
g
gildor
05/08/2019, 1:58 PMThere is
coroutineContext.isActive➕ 1
a
altavir
05/08/2019, 2:01 PMI do not have explicit instance of context.
We are talking about
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suspend fun doA(){
isActive
}There is probably a way to get a context from continuation, but it is not direct.
g
gildor
05/08/2019, 2:03 PMThis is intrinsic property coroutineContext in any suspend function
💯 1
a
altavir
05/08/2019, 2:04 PMYes, you are right, I did not know about it
m
Marko Mitic
05/08/2019, 2:05 PMthat's what we we're looking for
g
gildor
05/08/2019, 2:20 PMThis is an example of isActive usage
But keep in mind that isActive has a bit different semantics than yield, if you use it in a loop and do not call any suspend functions, this loop will not get chance to reschedule coroutines and it will just spin on this thread, which may be fine, but not for main thread for example
But I'm a bit confused about top level isActive property:
kotlinx.coroutines.isActive22 Views