The Fundamentals of Kotlin Coroutines Every Developer Should Know

The Fundamentals of Kotlin Coroutines Every Developer Should Know

Similar to how cross platform mobile app development is mainstream, technically, asynchronous or non-blocking programming is the new reality. When you’re making server-side, desktop or mobile applications, it is important to supply Associate in Nursing expertise that’s not solely fluid from the user’s perspective, however scalable once required.

Kotlin solves this downside in an exceedingly versatile approach by providing coroutine support at the language level and relegating most of the practicality to libraries.

As a bonus, coroutines not solely open the doors to asynchronous programming, however, conjointly give a wealth of different potentialities like concurrency and actors.

Kotlin, as a language, provides solely stripped low-level APIs in its commonplace library to change varied libraries to utilize coroutines. Unlike several different languages with similar capabilities, async and look aren’t keywords in Kotlin and aren’t even a part of its commonplace library. Moreover, Kotlin’s thought of suspending performance provides a safer and fewer fallible abstraction for asynchronous operations than futures and guarantees.

kotlinx.coroutines could be a made library for coroutines developed by JetBrains. It contains a variety of high-level coroutine-enabled primitives that this guide covers, together with launch, async, await and more.

This is an orient core option of kotlinx.coroutines with a series of examples, shared out into completely different topics.

In order to use coroutines, also as follow the examples during this guide, you would like to feature a dependency on the kotlinx-coroutines-core module.

Your First Coroutine

A coroutine is AN instance of suspendable computation. it’s conceptually just like a thread, within the sense that it takes a block of code to run that works at the same time with the remainder of the code. However, a coroutine isn’t guaranteed to any specific thread. it should suspend its execution in one thread and resume in another one.

Coroutines are thought of as light-weight threads. However, there’s a variety of vital variations that build their real-life usage terribly completely different from threads.

Below is the following result:


Let’s dissect what this code does.

  • Launch may be a coroutine builder. It launches a brand new coroutine at the same time with the remainder of the code.
  • Delay may be a special suspending operation. It suspends the coroutine for a selected time. Suspending a coroutine doesn’t block the underlying thread, however it permits different coroutines to run and use the underlying thread for his or her code.
  • runBlocking is additionally a coroutine builder that bridges the non-coroutine world of a daily fun main() and also the code with coroutines inside runBlocking  curling braces. This can be highlighted in AN IDE by this: CoroutineScope hint right once the runBlocking gap curling brace.

If you take away or forget runBlocking during this code, you will get a slip-up on the launch decision, since launch is asserted solely within the CoroutineScope:

The name runBlocking means the thread that runs it (in this scenario – the main thread) gets blocked for the given duration of the call, until all the codeblocks inside runBlocking { … } complete their execution. You will often observe runBlocking used to like that at the very top-level of the application and quite hardly inside the actual code, as threads are valuable resources and blocking them is ineffective.

Extract function refactoring

Let’s extract the block of code within launch  into a separate perform. After you do Extract perform refactoring on this code, you get a brand new performance of the suspend modifier. This can be the primary suspension performed. Suspending functions may be used within coroutines rather than regular functions, however, their further feature is that they’ll, in turn, use different suspending functions (like delay during this example) to suspend execution of a coroutine.

Scope builder

In addition to the coroutine scope provided by different builders, it’s possible to declare your own scope using the coroutineScope builder. It creates a coroutine scope and does not complete until all launched children are completed.

runBlocking and coroutineScope both look similar because they both wait for their body and all their children to complete. The main difference is that the runBlocking blocks the current thread for waiting, while coroutineScope just suspends, releasing the underlying thread for other usages. Because of this difference, runBlocking is a regular function and coroutineScope is a suspending function.

You can use coroutineScope from any suspending function. For an example, you can move the parallel logs of Hello and World into the suspend doWorld() function:

This code also prints:


Scope builder and concurrency

The coroutineScope builder can be used in any suspending function to perform multiple concurrent processes. Let’s launches two concurrent coroutines inside a doWorld suspending function:


Both functions of code inside launch { … } blocks execute parallely, with World1 printed first, after a second from start, and World2 printed next, after two seconds from start. coroutineScope in doWorld block completes only after both blocks are complete, so doWorld returns and allows the Done string to be printed only after that.

An explicit job

A launch coroutine builder returns a Job’s object that is a handle to the launched coroutine and can be used to forcefully wait for its completion. For example, you can wait for completion of the child coroutine and then print “Done” string will print:

And last Coroutines ARE light-weight

Above code launches 100K coroutines and after 5 seconds, each coroutine prints a dot.

Now, try that with threads (and remove runBlocking, replace launch with thread, and replace delay with Thread.sleep ). What would happen? (Most likely your code will produce out-of-memory error)


The purpose of this blog was to discuss briefly what Kotlin’s coroutines mechanisms are, how they work and how we will use them as an alternative way to asynchronous programming to be used in our day to day projects.

We believe you now have a better understanding of the concept. If you’re looking for a solid mobile application development company or specifically an Android app development company, you know our expertise now. Get in touch with us with your requirements today.

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Ahesanali Khanusiya

Sr. Software Developer (Mobile) at Dev Information Technology Ltd.
I am a passionate programmer who is always keen on learning more about latest technologies. I pride myself on learning as much as possible which helps to improve stability with better user experience in mobile application.

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