The Ultimate Guide on Kotlin Coroutines

When dealing with complex applications, the single path pattern of execution doesn’t help that much. In order to deal with complex applications, you have to implement a concurrency pattern of execution so that the code doesn’t block. The Kotlin coroutine is used to write concurrent and asynchronous programs. In this tutorial, you will learn all about Kotlin coroutines.

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Why Do You Need Coroutines?

In today’s world, nobody wants to wait for anything; all of us want to get a quick result out of anything as soon as possible, which is not feasible in many cases. Similarly, an application runs various tasks and operations, and the operating time for each task is different from others. As a result, sometimes, some tasks require quite a long time while others keep on waiting for their turn. While doing these time-consuming tasks, you need to ensure the user experience isn't degraded.

Asynchronous programming is used to provide a smooth flowing experience for the client-side and server-side. Now asynchronous means it can execute simultaneously multiple tasks, and other tasks don't need to wait for another task. It is easy to write the asynchronous code in Coroutines and it makes it more easy and readable by eliminating the requirement of callback pattern.

Now, you will learn about threads.

What Are Threads?

Before understanding coroutines, you have to understand threads. So you will start with programs; the programs are a set of instructions. Whenever a program runs, it creates a process that contains memory, process id, etc. In that process, some threads are used to execute the information.



Every process has at least one thread. These threads help with high-performance applications, and they work in sequential order one after the other.

Whenever a thread gets stuck while running an instruction, then the other thread executes the rest of the instructions.  

Now, go ahead and understand Kotlin Coroutines.

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What Are Kotlin Coroutines?

Coroutine stands for cooperating functions; it is derived from two words - co and routine. The word co stands for cooperation, and routine stands for functions. A coroutine is a feature of Kotlin; it can do all the things that a thread can and is also very efficient. They are lightweight threads that help to write simplified asynchronous code that keeps the application responsive while maintaining heavy tasks like network calls and avoiding tasks from blocking.

Coroutines are executed inside the thread and are also suspendable. Here suspendable means that you can execute some instructions, then stop the coroutine in between the execution and continue when you wish to. Coroutines can also switch between the threads, which gives coroutines an edge over threads.

So as you have understood Kotlin coroutines, now look at some coroutines' features.

Features of Coroutines

  1. Lightweight
  2. Fewer memory leaks
  3. Built-in cancellation support
  4. Jetpack integration
  • Lightweight: because of the support for the suspension, you can run many coroutines on a single thread, which doesn’t block the thread where the coroutine is running, which is why it is called lightweight. Coroutine has a collection of threads that can be used when required; when the task is done, the thread is kept back to the collection and reused when needed.
  • Fewer memory leaks: Kotlin coroutines follow the structured concurrency, which is why there are very less memory leaks in Kotin. This structured concurrency means it can only launch the new coroutine in a particular Coroutine scope, which sets the lifetime of the coroutine. During the implementation, a large number of coroutines are launched, and the structured concurrency takes care of those so that they are not lost or leaked.
  • Built-in cancellation support : Cancellation in coroutine is interactive. In order to be cancellable, a coroutine must be cooperative, but if it is not cooperative, then it will wait for the coroutine to finish. There are two ways to make a coroutine cancellable: using suspending functions through kotlin.coroutines like delay(), yield() etc that are cancellable and second using CoroutineScope.isActive boolean flag.
  • Jetpack integration: There are many libraries of Jetpack that provide support for Coroutines; for example, Android KTX is a set of Kotlin extensions that provide the android platform and other APIs, etc. The Jetpack is basically a collection of android development components that helps in building android apps and making complex things simple and easy.

Now, go ahead and understand the example of the Kotlin coroutine.

Example of Coroutines

You will see some terms related to coroutines and then have a look at an example.

  • Launch: Launch is a coroutine builder; it launches a new coroutine concurrently, i.e., without blocking the current thread. It automatically gets canceled when the resulting job is canceled, and it doesn’t return any result.
  • Async: Like the launch function, it is also used to launch a new coroutine; the only difference is that it returns a deferred instead of a Job. The deferred is a non-blocking future that promises to deliver the result later.  
  • Delay: Delay is a suspending function that is used to suspend a function for a particular time and resumes it after that time. It doesn't block the underlying thread but allows the other coroutines to run and use the underlying thread. Also, it is a cancellable function.
  • Runblocking: Runblocking is a coroutine builder; it runs a new coroutine and blocks the current thread until its completion. In other words, the thread that runs in it gets blocked for the given duration until all the code blocks inside the brackets of run-blocking complete their execution.



In this example, the race is started will be printed first; after that, the race continues will be printed. Then there is a global scope of coroutine launched in which the bidding which is started will be printed. After that, a delay function will suspend the coroutine for 2 seconds, but before those 2 seconds get to be completed, the run blocking function will block the main thread or the thread in which it is used. So The race is finished will be printed because it has less delay time which is 1 second. 


Now you will understand some basics of Kotlin Coroutines.

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Basics of Coroutine  

Some basics of coroutine include:

  • Scope builder: The Coroutine Scope is used to declare your own scope. Unlike the runBlocking, it just suspends and releases the threads underlying. It is used to set the scope for new coroutines. Coroutine scope is responsible for controlling the lifecycle of a group of coroutines and their context. The coroutine builder is an extension to the coroutine scope, and there are three examples of Coroutine builder, which are run blocking, async, and launch.
  • Explicit job: A job object is returned by the Launch Coroutine builder; its task is to wait for the child coroutine’s completion explicitly. Jobs act as a handle to the coroutine in the queue. Every coroutine that is created returns a job instance that identifies the coroutine uniquely and manages its lifecycle.
  • Suspending functions: Suspending functions are those functions that can be paused and then continued later. You can use them inside the coroutines and can also use other suspending functions. They are used for long-running operations and wait for them to complete without blocking. The syntax of the suspended function is the same as that of the normal function but with the addition of the suspend keyword.
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In this tutorial on Kotlin coroutines, you understood why you need Kotlin coroutines; you understood what are Coroutines, and what are threads. You also explored the features of coroutines and the basics of coroutines. You also learned some basic terms of Kotlin coroutines with the help of an example.

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Do you have any questions regarding this tutorial on Kotlin coroutines? If you do, then put them in the comments section. We’ll help you solve your queries. To learn more about Kotlin, click on the following link:

About the Author

Harsh BhardwajHarsh Bhardwaj

Harsh is a Research Analyst at Simplilearn. He has a good hand at C++, Java, CSS, SQL, and a good grasp of Kotlin language. Harsh is quite interested in traveling, spirituality, and playing football.

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