Learning Concurrency in Kotlin

Android's UI

Android's UI dispatcher has a rather interesting implementation. First's there's a HandlerContext class that takes an android.os.Handler and a name. And the dispatch function simply forwards the Runnable to the post() function of the handler:

public class HandlerContext(    private val handler: Handler,    private val name: String? = null) : CoroutineDispatcher(), Delay {    override fun dispatch(context: CoroutineContext, block: Runnable) {        handler.post(block)    }}

Then, an instance of it called UI is created. It passes the main looper and the name UI to the constructor:

val UI = HandlerContext(Handler(Looper.getMainLooper()), "UI")

In practice, the only dispatcher that should override isDispatchNeeded() is Unconfined. All the other dispatchers ...