Is there a reason to NOT use `MainDispatcher.immediate` over just regular `MainDispatcher`?

# coroutines

[Matej Drobnič]

Is there a reason to NOT use MainDispatcher.immediate over just regular MainDispatcher?

[louiscad]

Yes, allowing other coroutines to run (cooperatively), or worse, tight loops.

[Matej Drobnič]

tight loops

[Matej Drobnič]

you basically risk stack overflow here?

[louiscad]

No, you risk blocking the main thread.

[Matej Drobnič]

ok, but what specific to tight loops is the problem?

[Matej Drobnič]

or just the general blocking of the main thread?

[louiscad]

If you have a tight loop on a coroutine where the suspension points resume immediately, and you use the immediate main dispatcher, you get the main thread to block.

[elizarov]

In addition, it makes order of events in your code harder to reason about.

[Paul Woitaschek]

And the opposite? When should or would one use .immediate?

[elizarov]

There is some small performance benefit with immediate. I’m not Android developer to tell whether it even remotely important, but generally I would not trade a small performance improvement for a code that is harder to reason about.

[Paul Woitaschek]

But why is it even there then?

[elizarov]

Some people think that this performance benefit is worth it and we (in Kotiln) in general are trying to provide tools for as large number of use-cases as possible. However, we pick defaults on the safe side, that is why you have to explicitly opt-in to immediate if you needed and understand all the problems around it.

[Paul Woitaschek]

And can you write in the javadoc what the implications are?