Every fiber-blocking operation eventually ends up with a call to Fiber.park(). If you want to call park in your function or call a function that calls park etc., you need to let Quasar know that your function is "suspendable". There are several ways to do that: you can declare to throw a SuspendExecution exception, you can annotate your method with a @Suspendable annotation, or you could declare it as suspendable programmatically or in an external text file.