Trace_core (trace.Trace

type span = int64

A span identifier.

The meaning of the identifier depends on the collector.

type trace_id = string

A bytestring representing a (possibly distributed) trace made of async spans. With opentelemetry this is 16 bytes.

since NEXT_RELEASE

type user_data = [

| `Int of int
| `String of string
| `Bool of bool
| `Float of float
| `None

]

User defined data, generally passed as key/value pairs to whatever collector is installed (if any).

type explicit_span_ctx = {

span : span;
(*
The current span
*)
trace_id : trace_id;
(*
The trace this belongs to
*)

}

A context, passed around for async traces.

since NEXT_RELEASE

type explicit_span = {

span : span;
(*
Identifier for this span. Several explicit spans might share the same identifier since we can differentiate between them via meta.
*)
trace_id : trace_id;
(*
The trace this belongs to
*)
mutable meta : Meta_map.t;
(*
Metadata for this span (and its context). This can be used by collectors to carry collector-specific information from the beginning of the span, to the end of the span.
*)

}

Explicit span, with collector-specific metadata. This is richer than explicit_span_ctx but not intended to be passed around (or sent across the wire), unlike explicit_span_ctx.

module Collector : sig ... end

A global collector.

module Meta_map : sig ... end

module Level : sig ... end

Tracing levels.

Tracing

val enabled : unit -> bool

Is there a collector?

This is fast, so that the traced program can check it before creating any span or message.

val get_default_level : unit -> Level.t

Current default level for spans.

since 0.7

val set_default_level : Level.t -> unit

Set level used for spans that do not specify it. The default default value is Level.Trace.

since 0.7

val ctx_of_span : explicit_span -> explicit_span_ctx

Turn a span into a span context.

since NEXT_RELEASE

val with_span : 
  ?level:Level.t ->
  ?__FUNCTION__:string ->
  __FILE__:string ->
  __LINE__:int ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  (span -> 'a) ->
  'a

with_span ~__FILE__ ~__LINE__ name f enters a new span sp, and calls f sp. sp might be a dummy span if no collector is installed. When f sp returns or raises, the span sp is exited.

This is the recommended way to instrument most code.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.
NOTE an important restriction is that this is only supposed to work for synchronous, direct style code. Monadic concurrency, Effect-based fibers, etc. might not play well with this style of spans on some or all backends. If you use cooperative concurrency, see enter_manual_span.

val enter_span : 
  ?level:Level.t ->
  ?__FUNCTION__:string ->
  __FILE__:string ->
  __LINE__:int ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  span

Enter a span manually.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.

val exit_span : span -> unit

Exit a span manually. This must run on the same thread as the corresponding enter_span, and spans must nest correctly.

val add_data_to_span : span -> (string * user_data) list -> unit

Add structured data to the given active span (see with_span). Behavior is not specified if the span has been exited.

since 0.4

val enter_manual_span : 
  parent:explicit_span_ctx option ->
  ?flavor:[ `Sync | `Async ] ->
  ?level:Level.t ->
  ?__FUNCTION__:string ->
  __FILE__:string ->
  __LINE__:int ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  explicit_span

Like with_span but the caller is responsible for obtaining the parent span from their own caller, and carry the resulting explicit_span to the matching exit_manual_span.

NOTE this replaces enter_manual_sub_span and enter_manual_toplevel_span by just making parent an explicit option. It is breaking anyway because we now pass an explicit_span_ctx instead of a full explicit_span (the reason being that we might receive this explicit_span_ctx from another process or machine).

parameter flavor
a description of the span that can be used by the Collector.S to decide how to represent the span. Typically, `Sync spans start and stop on one thread, and are nested purely by their timestamp; and `Async spans can overlap, migrate between threads, etc. (as happens in Lwt, Eio, Async, etc.) which impacts how the collector might represent them.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.

since NEXT_RELEASE

val exit_manual_span : explicit_span -> unit

Exit an explicit span. This can be on another thread, in a fiber or lightweight thread, etc. and will be supported by backends nonetheless. The span can be obtained via enter_manual_sub_span or enter_manual_toplevel_span.

since 0.3

val add_data_to_manual_span : 
  explicit_span ->
  (string * user_data) list ->
  unit

add_data_explicit esp data adds data to the span esp. The behavior is not specified is the span has been exited already.

since 0.4

val message : 
  ?level:Level.t ->
  ?span:span ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  unit

message msg logs a message msg (if a collector is installed). Additional metadata can be provided.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.

parameter span
the surrounding span, if any. This might be ignored by the collector.

val messagef : 
  ?level:Level.t ->
  ?span:span ->
  ?data:(unit -> (string * user_data) list) ->
  ((('a, Stdlib.Format.formatter, unit, unit) format4 -> 'a) -> unit) ->
  unit

messagef (fun k->k"hello %s %d!" "world" 42) is like message "hello world 42!" but only computes the string formatting if a collector is installed.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.

val set_thread_name : string -> unit

Give a name to the current thread. This might be used by the collector to display traces in a more informative way.

val set_process_name : string -> unit

Give a name to the current process. This might be used by the collector to display traces in a more informative way.

val counter_int : 
  ?level:Level.t ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  int ->
  unit

Emit a counter of type int. Counters represent the evolution of some quantity over time.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.

parameter data
metadata for this metric (since 0.4)

val counter_float : 
  ?level:Level.t ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  float ->
  unit

Emit a counter of type float. See counter_int for more details.

parameter level
optional level for this span. since 0.7. Default is set via set_default_level.

parameter data
metadata for this metric (since 0.4)

Collector

type collector = (module Collector.S)

An event collector.

See Collector for more details.

val setup_collector : collector -> unit

setup_collector c installs c as the current collector.

raises Invalid_argument
if there already is an established collector.

val get_current_level : unit -> Level.t

Get current level. This is only meaningful if a collector was set up with setup_collector.

since 0.7

val set_current_level : Level.t -> unit

Set the current level of tracing. This only has a visible effect if a collector was installed with setup_collector.

since 0.7

val shutdown : unit -> unit

shutdown () shutdowns the current collector, if one was installed, and waits for it to terminate before returning.

Extensions

type extension_event = ..

Extension event

since 0.8

val extension_event : extension_event -> unit

Trigger an extension event, whose meaning depends on the library that defines it. Some collectors will simply ignore it. This does nothing if no collector is setup.

since 0.8