Chapters
Chapters

Chapters

Hide chapters

Kotlin Coroutines by Tutorials

Third Edition · Android 12 · Kotlin 1.6 · Android Studio Bumblebee

Before You Begin

Section 0: 6 chapters
Show chapters Hide chapters

Section I: Introduction to Coroutines

Section 1: 9 chapters
Show chapters Hide chapters

Section II: Channels & Flows

Section 2: 4 chapters
Show chapters Hide chapters

Section III: Coroutines & Android

Section 3: 6 chapters
Show chapters Hide chapters

9. Manage Cancellation
Written by Luka Kordić

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

When you initiate multiple asynchronous operations that are dependent on each other, the possibilities of one failing, then leading to others also failing, increases. This often means that the end result won’t be exactly what you expected. Coroutines address this problem and provide cancellation mechanisms to handle this and many other cases.

This chapter will dive deeper into the concepts and mechanics of cancellation in coroutines.

Cancelling a Coroutine

As with any multi-threading concept, the lifecycle of a coroutine can become a problem. You need to stop any potentially long-running background tasks when it is in an inconsistent state in order to prevent memory leaks or crashes. To resolve this, coroutines provide a simple cancelling mechanism.

Job Object

As you’ve seen in Chapter 3: “Getting Started With Coroutines”, when you launch a new coroutine using the launch coroutine builder, you get a Job object as the return value. This Job object represents the running coroutine, which you can cancel at any point by calling cancel().

Being Cooperative

In a long-running application, you might need fine-grained control on your background coroutines. For example, a task that launched a coroutine might have finished, and now its result is no longer needed; consequently, its operation can be canceled. This is where cancel() comes in.

CancellationException

Coroutines internally use CancellationException instances for cancellation, which are then ignored by all handlers. They are typically thrown by cancellable suspending functions if the Job of the coroutine is cancelled while it is suspending. It indicates normal cancellation of a coroutine.

Join, CancelAndJoin and CancelChildren

The Kotlin standard library provides a couple of convenience functions for handling coroutine completion and cancellation.

Timing Out

Long-running coroutines are sometimes required to terminate after a set time has passed. While you can manually track the reference to the corresponding Job and launch a separate coroutine to cancel the tracked one after a delay, the coroutines library provides a convenience function called withTimeout. To see it in action, open the WithTimeoutExample.kt file in the starter project, and use the code below.

Key Points

  • You can use cancel() on Job instances to cancel a coroutine.
  • Always make sure that your code is cooperative with cancellation.
  • All functions from the standard library support cancellation out of the box.
  • When the parent coroutine is canceled, all of its children are recursively canceled, too.
  • Coroutines manage cancellation internally by using CancellationException.
  • CancellationException is not printed to the console/log by the default uncaught exception handler.
  • Using the withTimeout function, you can terminate a long-running coroutine after a set time has elapsed.

Where to Go From Here?

Being able to cancel an ongoing task is almost always required. The cycle of starting a coroutine and canceling it when an exception is thrown or when the business logic demands it is part of some of the common patterns in programming. Coroutines in Kotlin were built keeping that in mind since the very beginning.

8. Exception Handling
10. Building Sequences & Iterators With Yield
Have a technical question? Want to report a bug? You can ask questions and report bugs to the book authors in our official book forum here.
© 2026 Kodeco Inc.

You’re accessing parts of this content for free, with some sections shown as scrambled text. Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now