Function tracing::subscriber::set_default

pub fn set_default<S>(subscriber: S) -> DefaultGuard where
    S: Subscriber + Send + Sync + 'static, 

Sets the subscriber as the default for the duration of the lifetime of the returned DefaultGuard

The default subscriber is used when creating a new Span or Event, if no span is currently executing. If a span is currently executing, new spans or events are dispatched to the subscriber that tagged that span, instead.