Trace_subscriber.Span_tbl
A table that can be used to remember information about spans.
This is convenient when we want to rememner information from a span begin, when dealing with the corresponding span end.
NOTE: this is thread safe when threads are enabled.
val create : unit -> 'v t
val add : 'v t -> Trace_core.span -> 'v -> unit
val find_exn : 'v t -> Trace_core.span -> 'v
val remove : _ t -> Trace_core.span -> unit
Remove the span if present
val to_list : 'v t -> (Trace_core.span * 'v) list