Module Trace_subscriber.Callbacks

Callbacks used for subscribers.

Each subscriber defines a set of callbacks, for each possible tracing event. These callbacks take a custom state that is paired with the callbacks in Subscriber.t.

To use a default implementation for some callbacks, use:

  module My_callbacks = struct
    type st = …

    include Trace_subscriber.Callbacks.Dummy

    let on_init (state:st) ~time_ns : unit = …

    (* … other custom callbacks … *)
  end

NOTE: the trace_id passed alongside manual spans is guaranteed to be at least 64 bits.

module type S = sig ... end

First class module signature for callbacks

type 'st t = (module S with type st = 'st)

Callbacks for a subscriber. There is one callback per event in Trace. The type 'st is the state that is passed to every single callback.

module Dummy : sig ... end

Dummy callbacks. It can be useful to reuse some of these functions in a real subscriber that doesn't want to handle all events, but only some of them.

val dummy : unit -> 'st t

Dummy callbacks, ignores all events.