Function run_async 

pub fn run_async<T, Fut, C>(fut: Fut, cancel: Option<CancelToken>, complete: C)
where
    T: 'static,
    Fut: Future<Output = Result<T, FfiError>> + Send + 'static,
    C: FnOnce(Result<T, FfiError>) + Send + 'static,

Run an async export to completion and deliver its result exactly once.

fut is the producer’s work, already mapped to Result<T, FfiError> (a domain error becomes its FfiError); complete lowers the outcome into the C completion callback’s slots and invokes it. The runtime calls complete exactly once:

• with fut’s result when it resolves;
• with a PANIC_ERROR_CODE error when polling it panics;
• with CANCELLED_ERROR_CODE as soon as cancel fires, after dropping fut, or when the executor drops the task before it resolves;
• with GENERIC_ERROR_CODE when the executor can’t take the task (see spawn).