Coroutine context and dispatchers in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to launch a coroutine on the IO dispatcher.

Kotlin

GlobalScope.launch([1]) {
    println("Running in IO dispatcher")
}

Drag options to blanks, or click blank then click option'

ADispatchers.Default

BDispatchers.Main

CDispatchers.IO

DDispatchers.Unconfined

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.Main for IO tasks causes blocking on the main thread.

Using Dispatchers.Default is for CPU-intensive tasks, not IO.

The IO dispatcher is used for offloading blocking IO tasks to a shared pool of threads.

2fill in blank

medium

Complete the code to switch the coroutine context to the Default dispatcher.

Kotlin

withContext([1]) {
    println("Running in Default dispatcher")
}

Drag options to blanks, or click blank then click option'

ADispatchers.IO

BDispatchers.Default

CDispatchers.Main

DDispatchers.Unconfined

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.IO for CPU tasks is inefficient.

Dispatchers.Main is for UI thread, not CPU work.

Dispatchers.Default is used for CPU-intensive work like sorting or parsing.

3fill in blank

hard

Fix the error in the coroutine builder to use the correct dispatcher for UI updates.

Kotlin

GlobalScope.launch([1]) {
    // Update UI here
    println("Updating UI")
}

Drag options to blanks, or click blank then click option'

ADispatchers.Main

BDispatchers.Default

CDispatchers.Unconfined

DDispatchers.IO

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.IO or Default causes exceptions when updating UI.

Unconfined dispatcher may run on any thread, unsafe for UI.

UI updates must happen on the Main dispatcher which runs on the main thread.

4fill in blank

hard

Fill both blanks to create a coroutine context combining a Job and the Default dispatcher.

Kotlin

val job = Job()
val context = job + [1]

GlobalScope.launch(context) {
    println("Running with combined context")
}

Drag options to blanks, or click blank then click option'

ADispatchers.Default

BDispatchers.IO

CDispatchers.Main

DDispatchers.Unconfined

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.IO here is for IO, not CPU work.

Dispatchers.Main is for UI, not combined with Job for CPU tasks.

Combining a Job with Dispatchers.Default creates a context for CPU work with cancellation support.

5fill in blank

hard

Fill all three blanks to create a coroutine that runs on the IO dispatcher, with a SupervisorJob and a custom CoroutineName.

Kotlin

val supervisor = [1]()
val context = supervisor + [2] + [3]("MyCoroutine")

GlobalScope.launch(context) {
    println("Running supervised coroutine with name")
}

Drag options to blanks, or click blank then click option'

AJob

BDispatchers.IO

CCoroutineName

DSupervisorJob

Attempts:

3 left

💡 Hint

Common Mistakes

Using Job instead of SupervisorJob loses supervision benefits.

Using Dispatchers.Default instead of IO changes the thread pool.

Forgetting CoroutineName loses coroutine identification.

SupervisorJob allows independent child coroutines, Dispatchers.IO is for IO tasks, and CoroutineName adds a name for debugging.