Book Image

Learning Concurrency in Kotlin

By : Miguel Angel Castiblanco Torres
Book Image

Learning Concurrency in Kotlin

By: Miguel Angel Castiblanco Torres

Overview of this book

Kotlin is a modern and statically typed programming language with support for concurrency. Complete with detailed explanations of essential concepts, practical examples and self-assessment questions, Learning Concurrency in Kotlin addresses the unique challenges in design and implementation of concurrent code. This practical guide will help you to build distributed and scalable applications using Kotlin. Beginning with an introduction to Kotlin's coroutines, you’ll learn how to write concurrent code and understand the fundamental concepts needed to write multithreaded software in Kotlin. You'll explore how to communicate between and synchronize your threads and coroutines to write collaborative asynchronous applications. You'll also learn how to handle errors and exceptions, as well as how to work with a multicore processor to run several programs in parallel. In addition to this, you’ll delve into how coroutines work with each other. Finally, you’ll be able to build an Android application such as an RSS reader by putting your knowledge into practice. By the end of this book, you’ll have learned techniques and skills to write optimized code and multithread applications.
Table of Contents (11 chapters)

Non-happy path – Unexpected crash

Let's take a look at how we are waiting for each deferred to complete:

private fun asyncLoadNews() = launch {
val requests = mutableListOf<Deferred<List<String>>>()

feeds.mapTo(requests) {
asyncFetchHeadlines(it, dispatcher)
}

requests.forEach {
it.await()
}

...
}

Since we are using await() to wait for the completion of our coroutines, any exception happening inside them will be propagated to the current thread. This means that there are two scenarios in which the application will crash easily:

  • There's no internet connection
  • The URL of one or more feeds is invalid or incorrect

Let's test one of those out. We can add an invalid URL to the list of feeds, which is something like this:

private val feeds = listOf(
"https://www.npr.org/rss/rss.php?id=1001",
...