Coroutines in Controllers and Exception Handling

[srinunagulapalli]

In our micronaut-kotlin project, we are making the controller endpoints suspendable by using the suspend keyword and are executing the code inside the controller endpoint by starting a coroutineScope like below:

suspend fun statusDelayed() {
    coroutineScope{
        // code execution block
    }
}

We are not throwing exceptions anywhere down the line in the application and using Arrow's Either to wrap any errors/exceptions. When the execution reaches back the controller, what happens if we unwrap this exception from the Either and throw the exception in the controller?

1. How does micronaut handle under the hood when a coroutineScope is used in controller endpoint? will it launch a coroutine under the hood?
2. Will the exception thrown in the controller endpoint have an impact on the other controller endpoints (that would have already been launched if micronaut starts a coroutine for each controller endpoint)?
3. Will a GlobalExceptionHandler configured with @Error(global = true) handle gracefully and catch immediately if an exception is thrown from a controller endpoint?
4. What is the recommended way to handle exceptions and errors in a micronaut kotlin project that deals with coroutines.

[yawkat]

In general, suspend methods are handled exactly like reactive methods. So if a controller suspends and then throws an exception (like you seem to describe), that exception will be handled as if the controller returned a Mono.error(exc). Which means it'll be handled as if the controller threw the exception directly immediately.