Whats the recommended approach for using `scope.launch {}` from MainScope? Generally, the task itsel...

# coroutines

[Zoltan Demant]

Whats the recommended approach for using scope.launch {} from MainScope? Generally, the task itself will run with the "correct" dispatcher, for example: loading something from a database is always executed using withContext(<http://Dispatchers.IO|Dispatchers.IO>).

But to me it seems that I might as well specify something like Dispatchers.Default in the launch block, so that all tasks are at least off-loaded from the main thread by default? As a real life scenario, I was just working on an issue where UI froze after the user had selected a file to import from; I had failed to realize that contentResolver.openInputStream(uri) was blocking rather than reading from the inputStream itself. If I had been using Dispatchers.Default, this wouldnt have been a problem. Now, instead I have to wrap each individual call like this (there arent many, but still) in a withContext(Dispatchers.Default/IO).

[Robert Williams]

I'd say it's a hacky workaround that hides bugs rather than fixes them

[Robert Williams]

If you have a suspend fun that blocks the calling thread that's always a bug in the suspend fun and not the caller's responsibility

[tseisel]

Not all coroutines launched within the MainScope are expected to execute blocking operations. Sometimes you just need to execute suspend UI operations, for example waiting for a delay before retrying an operation.
suspend functions should be main-safe, i.e. they should be designed to use another dispatcher internally, so that callers may run on any dispatcher without worying about blocking the main thread.

[Robert Williams]

All of coroutines has been designed that the caller shouldn't know about threading details of things it calls

[Robert Williams]

Blocking coroutines make your code less reusable (because everywhere needs to know to launch on a background thread)

[Robert Williams]

And makes cancellation harder (because normally withContext acts as a yield point)

[Robert Williams]

Plus assuming you have a single threaded UI-toolkit (otherwise you wouldn't care about blocking main thread) you'll need another context switch at the end to get back to main anyway

[Zoltan Demant]

Thank you both, this is exactly what I needed to hear to understand that its actually a bad idea 🤌🏽