Kotlin Coroutines

In this tutorial, you'll learn about Fix Kotlin Coroutines Not Launching. We cover key concepts, practical examples, and best practices.

The Problem

Coroutines launched with launch {} do not execute or complete.

Quick Fix

Use coroutine scope

Wrong:

launch {
    delay(1000)
    println("Done")
} // No scope

Output:

No coroutine scope

Right:

CoroutineScope(Dispatchers.Default).launch {
    delay(1000)
    println("Done")
}

Output:

Coroutine launched in scope

Use runBlocking for tests

Wrong:

fun test() {
    launch {
        delay(1000)
        println("Done")
    }
} // Test ends before completion

Output:

Test exits early

Right:

fun test() = runBlocking {
    launch {
        delay(1000)
        println("Done")
    }
}

Output:

Test waits for coroutine

Handle coroutine exceptions

Wrong:

scope.launch {
    throw RuntimeException()
} // Uncaught

Output:

Crash

Right:

scope.launch {
    try {
        // risky
    } catch (e: Exception) {
        log.error("Error", e)
    }
}

Output:

Exception handled

Prevention

• Use CoroutineScope to launch coroutines
• Use runBlocking for tests
• Always handle exceptions within coroutines

Common Mistakes with coroutines

1. Using return to exit a function early instead of wrapping a pure value in the monad
2. Mixing let bindings with <- bindings in do notation, producing type errors
3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

These mistakes appear frequently in real-world KOTLIN code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

This quick fix is part of the DodaTech Spring & JVM ecosystem series. Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro.