_preconditionSafeToWait(file:line:)
Must crash if it is not safe to call wait() on an EventLoopFuture.
func _preconditionSafeToWait(file: StaticString, line: UInt) This method is a debugging hook that can be used to override the behaviour of EventLoopFuture.wait() when called. By default this simply becomes preconditionNotInEventLoop, but some EventLoops are capable of more exhaustive checking and can validate that the wait is not occurring on an entire EventLoopGroup, or even more broadly.
This method should not be called by users directly, it should only be implemented by EventLoop implementers that need to customise the behaviour.