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Top 10 Coroutine Mistakes We All Have Made as Android Developers

Dobri KostadinovNovember 22, 2024About 6 minJavaKotlinAndroidArticle(s)blogdroidcon.comjavakotlinandroid

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Top 10 Coroutine Mistakes We All Have Made as Android Developers
As Android developers, Kotlin coroutines have become an indispensable tool in our asynchronous programming toolkit. They simplify concurrent tasks, make code more readable, and help us avoid the callback hell that was prevalent with earlier approaches. However, coroutines come with their own set of challenges, and it’s easy to fall into common pitfalls that can lead to bugs, crashes, or suboptimal performance.

Introduction

As Android developers, Kotlin coroutines have become an indispensable tool in our asynchronous programming toolkit. They simplify concurrent tasks, make code more readable, and help us avoid the callback hell that was prevalent with earlier approaches. However, coroutines come with their own set of challenges, and it’s easy to fall into common pitfalls that can lead to bugs, crashes, or suboptimal performance.

In this article, we’ll explore the top 10 coroutine mistakes that many of us have made (often unknowingly) and provide guidance on how to avoid them. Whether you’re a seasoned developer or just starting with coroutines, this guide aims to enhance your understanding and help you write more robust asynchronous code.


1. Blocking the Main Thread

The Mistake

Running long-running or blocking tasks on the Main dispatcher, which can freeze the UI and lead to Application Not Responding (ANR) errors.

Example

// Wrong
GlobalScope.launch {
    // Long-running task
}

// Correct
GlobalScope.launch(Dispatchers.IO) {
    // Long-running task
}

Use Dispatchers.IO for I/O operations and Dispatchers.Default for CPU-intensive tasks. Reserve Dispatchers.Main for updating the UI.


2. Ignoring Coroutine Scope Hierarchy

The Mistake

Not properly structuring coroutine scopes, leading to unmanaged coroutines that outlive their intended lifecycle, causing memory leaks or crashes.

Example

// In a ViewModel
viewModelScope.launch {
    // Coroutine work
}

This ensures that coroutines are cancelled appropriately when the associated lifecycle is destroyed.


3. Mishandling Exception Propagation

The Mistake

Failing to handle exceptions within coroutines properly, which can cause unexpected crashes or silent failures.

Example

viewModelScope.launch {
    try {
        // Suspended function that might throw an exception
    } catch (e: Exception) {
        if (e !is CancellationException) {
            // Handle exception
        } else {
            throw e // Rethrow to respect cancellation
        }
    }
}

Alternatively, use a CoroutineExceptionHandler for unhandled exceptions:

val exceptionHandler = CoroutineExceptionHandler { \_, throwable ->
    if (throwable !is CancellationException) {
        // Handle unhandled exception
    }
}

viewModelScope.launch(exceptionHandler) {
    // Suspended function that might throw an exception
}

4. Using the Wrong Coroutine Builder

The Mistake

Confusing launch and async builders, leading to unintended behavior, such as missing results or unnecessary concurrency.

Example

// Using async when you need a result
val deferredResult = async {
    computeValue()
}
val result = deferredResult.await()

5. Overusing GlobalScope

The Mistake

Relying on GlobalScope for launching coroutines, which can lead to coroutines that run longer than needed and are difficult to manage.


6. Not Considering Thread Safety

The Mistake

Accessing or modifying shared mutable data from multiple coroutines without proper synchronization, leading to race conditions.

Example using Mutex

val mutex = Mutex()
var sharedResource = 0

coroutineScope.launch {
    mutex.withLock {
        sharedResource++
    }
}

7. Forgetting to Cancel Coroutines

The Mistake

Not cancelling coroutines when they’re no longer needed, which can waste resources or cause unintended side effects.

Example

val job = CoroutineScope(Dispatchers.IO).launch {
    // Work
}

// Cancel when done
job.cancel()

8. Blocking Inside Coroutines

The Mistake

Using blocking calls like Thread.sleep() or heavy computations inside coroutines without switching to an appropriate dispatcher, which can block the underlying thread.

Example

// Wrong
launch(Dispatchers.IO) {
    Thread.sleep(1000)
}

// Correct
launch(Dispatchers.IO) {
    delay(1000)
}

9. Misusing withContext

The Mistake

Using withContext incorrectly, such as nesting it unnecessarily or misunderstanding its purpose, leading to code that’s hard to read or inefficient.

Example

// Correct usage
val result = withContext(Dispatchers.IO) {
    // Perform I/O operation
}

10. Not Testing Coroutines Properly

The Mistake

Neglecting to write proper tests for coroutine-based code, or writing tests that don’t handle coroutines correctly, leading to flaky or unreliable tests.

Example

@Test
fun testCoroutine() = runTest {
    val result = mySuspendingFunction()
    assertEquals(expectedResult, result)
}

Conclusion

Coroutines are powerful, but with great power comes great responsibility. By being aware of these common mistakes and understanding how to avoid them, you can write more efficient, reliable, and maintainable asynchronous code in your Android applications.

Remember:

  • Always choose the correct dispatcher.
  • Tie your coroutines to the appropriate lifecycle.
  • Handle exceptions thoughtfully.
  • Be mindful of coroutine scopes and cancellation.
  • Test your coroutine code thoroughly.

By following these best practices, you’ll harness the full potential of Kotlin coroutines and provide a smoother, more responsive experience for your app users.

Info

This article is previously published on proandroiddev

Top 10 Coroutine Mistakes We All Have Made as Android Developers
Understanding and Avoiding Common Pitfalls in Asynchronous Programming with Kotlin Coroutines
Top 10 Coroutine Mistakes We All Have Made as Android Developers

As Android developers, Kotlin coroutines have become an indispensable tool in our asynchronous programming toolkit. They simplify concurrent tasks, make code more readable, and help us avoid the callback hell that was prevalent with earlier approaches. However, coroutines come with their own set of challenges, and it’s easy to fall into common pitfalls that can lead to bugs, crashes, or suboptimal performance.