Hands-On Design Patterns with Kotlin

Waiting for a coroutine

Up until now, to let our asynchronous code complete, we've used either Thread.sleep() or CountDownLatch. But there are better options with threads and coroutines. Much like Thread, a job has the join() function. By invoking it, we can wait for the execution of the coroutine to complete.

Take a look at the following code:

val j = launch(CommonPool) {    for (i in 1..10_000) {        if (i % 1000 == 0) {            println(i)            yield()        }    }}

Although it should have printed 10 lines, it doesn't print anything, actually. That's because our main thread terminates before giving a coroutine a chance to start.

By adding the following lines, our example will print the expected results:

runBlocking {    j.join()}

What about this runBlocking, you ask? ...