Job lifecycle and cancellation in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Job in Kotlin coroutines?

A Job represents a cancellable task or coroutine. It controls the coroutine's lifecycle, allowing you to start, cancel, or check its status.

intermediate

Name the main states in a Job's lifecycle.

The main states are:

• New: Created but not started.
• Active: Running or suspended.
• Completing: Finishing work.
• Cancelled: Stopped before completion.
• Completed: Finished successfully.

beginner

How do you cancel a Job in Kotlin?

You call the cancel() function on the Job instance. This requests cancellation, and the coroutine cooperatively stops if it checks for cancellation.

intermediate

What happens if a coroutine ignores cancellation?

If a coroutine does not check for cancellation (e.g., by calling yield() or checking isActive), it may continue running even after cancel() is called, delaying cancellation.

intermediate

Explain cooperative cancellation in Kotlin coroutines.

Cooperative cancellation means the coroutine must regularly check if it is cancelled and stop work accordingly. This is done by checking isActive or using cancellable suspending functions.

Which function is used to stop a running Job in Kotlin?

A cancel()

B stop()

C terminate()

D end()

The cancel() function requests cancellation of a Job.

What state is a Job in when it has finished successfully?

A Active

B Cancelled

C New

D Completed

A Job is Completed when it finishes its work successfully.

What must a coroutine do to respond to cancellation?

A Check for cancellation cooperatively

B Ignore cancellation requests

C Call cancel() on itself

D Run on a separate thread

Coroutines must cooperatively check for cancellation to stop execution.

Which of these is NOT a Job lifecycle state?

A New

B Active

C Paused

D Cancelled

There is no Paused state in Job lifecycle.

What happens if you call cancel() on a Job but the coroutine never checks for cancellation?

A The coroutine stops immediately

B The coroutine ignores cancellation and keeps running

C An error is thrown

D The Job restarts automatically

Without cooperative checks, the coroutine keeps running despite cancellation requests.

Describe the lifecycle of a Kotlin Job and how cancellation affects it.

Think about how a Job moves from new to completed or cancelled.

Explain why cooperative cancellation is important in Kotlin coroutines.

Consider what happens if a coroutine ignores cancellation.