I <read today> that `kotlinx.coroutines.delay` on Android uses `Handler.postDelayed` under the hood....

# coroutines

[jeff]

I read today that kotlinx.coroutines.delay on Android uses Handler.postDelayed under the hood. That surprised me -- is it true? For Dispatcher.Main only, or all dispatchers?

[Zach Klippenstein (he/him) [MOD]]

Of the official Dispatchers.* dispatchers, it’s only for Dispatchers.Main, and only on Android. It’s also for any custom dispatchers derived from `Handler`s (thanks @Adam Powell for the correction). On jvm, delay uses the AWT/Swing event loop. The whole point of Dispatchers.Main is that it delegates to the current platform’s main thread event loop.

[mateusz.kwiecinski]

I can only add related source code: https://github.com/Kotlin/kotlinx.coroutines/blob/master/ui/kotlinx-coroutines-android/src/HandlerDispatcher.kt#L55 and its documentation 🙂 I consider kotlin and coroutines implementation well-written and it usually clears all doubts one may have. I hope you’ll find it useful as well 🙂

[jeff]

Thanks!

[Adam Powell]

It's for any dispatcher derived from a Handler, anyway.