There are

newSingleThreadContext

and

newFixedThreadPoolContext

provided by coroutines library out of box, and you can construct your own

CoroutineContext

based on any

ExecutorService

like this:

open class BaseCoroutineDispatcher(private val executor: ExecutorService) : CoroutineDispatcher() {
    override fun dispatch(context: CoroutineContext, block: Runnable) {
        executor.execute(block)
    }
}