Kotlin coroutine exception silently swallowed in launch

Problem

Exceptions thrown inside a coroutine launched with launch{} are silently swallowed and do not crash the app or appear in logs.

Symptoms

• No error log for failed coroutine
• App continues running after exception in coroutine
• Try-catch outside launch does not catch the exception

Stack

Solution

Install a CoroutineExceptionHandler or use supervisorScope. With structured concurrency, uncaught exceptions in launch propagate to the parent. With GlobalScope or SupervisorJob, they are delivered to the CoroutineExceptionHandler.

Code

// Option 1: CoroutineExceptionHandler
val handler = CoroutineExceptionHandler { _, throwable ->
    Log.e("Coroutine", "Uncaught exception", throwable)
}
scope.launch(handler) {
    throw RuntimeException("This will be logged")
}

// Option 2: Use async + await (exception thrown on await)
val deferred = scope.async {
    throw RuntimeException("error")
}
try {
    deferred.await()
} catch (e: RuntimeException) {
    // handle
}

// Option 3: try-catch inside launch
scope.launch {
    try {
        riskyOperation()
    } catch (e: Exception) {
        Log.e("TAG", "Failed", e)
    }
}

Caveats

CoroutineExceptionHandler only works with launch, not with async. For async, the exception is thrown when you call await().