Using The Event Logging Framework¶
Developers of most modules should consider generating useful information for the Logging subsystem.
In the Octez code base, logging is instrumented using an asynchronous event system, where log events are emitted in various part of the code and consumed by the so called sinks. This is done by using the tezos-event-logging library.
We use two levels of abstraction to define these events. Heavy events are defined using the most generic API and have the full expressive power and structure while being 100% lazy. Simple events are record-like structures which are constructed on top of the generic event api, and are meant to be less verbose and more developer friendly.
Simple events are record-like structures which are constructed directly (i.e. there is no high-level OCaml type, and parsing events is not accessible programmatically). The API is a bit less lazy than with the generic API (the fields of the events are still evaluated every time, which is usually not an issue since they are evaluated anyway by the application code itself).
See for instance src/bin_node/node_config_file.ml (search for the string declare_):
one declares typed-record events with
and they are called with
val Simple.emit: 'a Simple.t -> 'a -> (unit, trace) result Lwt.t.
Please read the guidelines that are documented in the Internal_event.Simple module.
The most generic API for defining events
Internal_event.Make gives full
expressive power and structure while being 100% lazy.
See for instance:
one needs to call the functor
module Event = Internal_event.Make(Definition)where
val Event.emit: ?section:Section.t -> (unit -> Block_seen_event.t) -> (unit, trace) result Lwt.t.
A sink is a module of type
Internal_event.SINK which is registered
within the system (just like events or errors kinds) using:
let () = Internal_event.All_sinks.register (module My_sink). Its
chosen URI-scheme should be unique.
See for instance: