Let me know if there is better way ⤴️

There is no better way for now. Currently, this a real issue with coroutines, one can easily forget to bind his jobs with Android activity, HTTP request lifecycle etc. and there is no way to enforce such binding. We have some thoughts about changing it: forbid top-level

async

and

launch

(and other top-level builders as well), define them as extensions on some parent job and provide an easy way to expose such parent job via android integration, new builders etc. The idea behind this approach is to make ownership of a job (actor, channel, cold stream, w/e) explicit in code, so cancellation will never be an issue. Then your example will be rewritten as

class MyFragment : Fragment() {
  fun loadData() = lifecycle.job().launch(UI) {} // <- job() is extension on lifecycle, won't compile if one tries to write fun loadData() = launch(UI) {}
}

Why do we want to do it if it will require more effort to write concurrent code (and break a lot of existing examples)? Consider the following snippet:

suspend fun computation() {
   val d1 = async {...}
   val d2 = async {...}
   return merge(d1.await(), d2.await())
}

If

d1

will throw an exception, no one will be able to cancel

d2

. And if

d2

throws another exception, no one will ever observe it! Though one may argue that it’s a programmer fault, this is how coroutines are usually recommended to be used (actually, it’s a simplified example from our guide). If

async

always should have a receiver,

computation

can be written only using some builder, e.g.:

suspend fun computation() = job {
   val d1 = async {...} // implicit receiver on `job {}` 
   val d2 = async {...}
   return merge(d1.await(), d2.await())
} // <- here builder will cancel launched tasks if necessary

Now all launched tasks will be properly cancelled/awaited in the end of

job {}

and it’s not possible to write

computation

without any builder. To launch jobs from non-suspendable contexts we will provide something like

Eternal.async {}

, where

Eternal

is

object

, so it always will be imported explicitly and code becomes more self-documented: “this job is launched via Eternal, so it can’t be cancelled as part of parent-child hierarchy and either it’s a mistake or it’s a system-wide job”. Opinions about this idea (note: it’s only a draft, not even prototyped) are welcome

Hmm that’s interesting approach. So, e.g. my typical android code would look like this:

val job = Job()
fun loadData() = job.launch(UI) {
    val result = withContext(CommonPool) { ... }
    view.showResult(result)
}

e.g. my typical android code would look like this

Empty jobs are not recommended, it doesn’t really make sense. Job should be bond with either your Android activity or another job.

But, if I want to launch another coroutine how I can achieve that

async

builder itself will have job (or something similar to it) as receiver, so nested async will work as expected:

val loadData() = job.launch(UI) {
   val innerTask = async(CommonPool) {}
   // Here inner task implicitly inherits job of UI activity and will be cancelled when activity is destroyed
}

Empty jobs are not recommended, it doesn’t really make sense.

I have made empty job to cancel it in activity

onDestroy

function. (because lifecycle aware stuff is available from library only, it’s not part of android sdk). With lifecycle callback it will look like in your sample

lifecycle.job().launch(UI)

.

Thanks for clarification, then your example is fine.

withContext

will stay correct, but this part of design is not yet properly investigated. Probably

withContext

should have job as well

If

withContext

need job as well, it would require write more code. E.g. currently in http client

fun loadUser(id: String, 
                       context: CoroutineContext = CommonPool) = withContext(context) {
    // logic
}

With new design:

fun loadUser(id: String, context: CoroutineContext = CommonPool, job: Job) 
= job.withContext(context) {
    // logic
}

I will have to pass job everywhere, am I right?

In such cases (when no one can cancel your task) you can use

Eternal

.

fun loadUser(id: String, context: CoroutineContext) = Eternal.withContext(context) {
    // logic
}

Doesn't a suspend fun have a coroutineContext...? withContext will only work in suspend fun...