12 tips to mastering Kotlin Coroutines

1. Always Use Structured Concurrency

Launch coroutines within a lifecycle-aware scope like viewModelScope or lifecycleScope to automatically cancel work when the UI (e.g., Activity/Fragment) is destroyed. No more memory leaks.

viewModelScope.launch {  
    // Coroutine dies automatically if the ViewModel is cleared  
}

2. Prefer withContext Over async for Single Operations

For a single background task, use withContext instead of async-await. It’s simpler and avoids unnecessary boilerplate:

suspend fun fetchData(): Data = withContext(Dispatchers.IO) {  
    // Network call or DB operation  
}

3. Use async Only for Parallel Tasks

When you need multiple independent operations to run concurrently, use async and await their results together:

val userDeferred = async { fetchUser() }  
val postsDeferred = async { fetchPosts() }  
val (user, posts) = awaitAll(userDeferred, postsDeferred)

4. Never Use GlobalScope

GlobalScope lives for the entire app lifecycle and can cause memory leaks. Always tie coroutines to a lifecycle-aware scope (see Tip #1).

5. Switch Dispatchers Wisely

• Dispatchers.Main: UI updates.
• Dispatchers.IO: Network, DB, or file operations.
• Dispatchers.Default: CPU-heavy work (e.g., sorting, parsing).
  Avoid hardcoding dispatchers—inject them for easier testing.

6. Handle Exceptions Gracefully

Use try/catch or a CoroutineExceptionHandler to avoid crashes:

val handler = CoroutineExceptionHandler { _, exception ->  
    Log.e("CoroutineError", "Caught: $exception")  
}  
viewModelScope.launch(handler) {  
    // Risky code here  
}

CoroutineExceptionHandler suits more for edge-cases or global handlers on top of a try/catch

7. Cancel Coroutines Properly

• Cancel manually with job.cancel() if needed.
• Check for cancellation with ensureActive() in long-running tasks

suspend fun heavyWork() {  
    repeat(100) { i ->  
        ensureActive() // Throws if coroutine is cancelled  
        // Do work  
    }  
}

8. Use SupervisorJob for Independent Child Coroutines

A SupervisorJob ensures a failing child coroutine doesn’t cancel its siblings (useful in UIs where one failed operation shouldn’t break others):

val scope = CoroutineScope(SupervisorJob() + Dispatchers.Main)

9. Test Coroutines with runTest

Use Kotlin’s kotlinx-coroutines-test library to avoid flaky tests:

@Test  
fun testFetchData() = runTest {  
    val data = repository.fetchData()  
    assertEquals(expectedData, data)  
}

10. Debounce User Input with Flows

Use Flow to handle rapid UI events (e.g., search bars) efficiently:

searchTextField.textChanges()  
    .debounce(300) // Wait 300ms after last input  
    .flatMapLatest { query ->  
        searchRepository.search(query)  
    }  
    .collect { results ->  
        updateUI(results)  
    }

11. Avoid Blocking Calls

Replace Thread.sleep() with delay(), which suspends without blocking the thread:

// ✅ Good  
delay(1000)  

// ❌ Bad  
Thread.sleep(1000)

12. Use coroutineScope for Scoped Parallelism

Need parallel tasks inside a suspend function? Wrap them with coroutineScope to ensure all children complete before returning:

suspend fun fetchAllData() = coroutineScope {  
    val data1 = async { fetchFromSource1() }  
    val data2 = async { fetchFromSource2() }  
    combineData(data1.await(), data2.await())  
}

Bonus:

Enable coroutine debugging in Android Studio by adding -Dkotlinx.coroutines.debug to your VM options. Track coroutine names and statuses in logs!

What’s your favorite coroutine hack? Share below! 👇