trace 0.5 · OCaml Package

Trace.

type span = int64

A span identifier.

The meaning of the identifier depends on the collector.

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 = {

span : span;
(*
Identifier for this span. Several explicit spans might share the same identifier since we can differentiate between them via meta.
*)
mutable meta : Meta_map.t;
(*
Metadata for this span (and its context)
*)

}

Explicit span, with collector-specific metadata

module Collector : sig ... end

A global collector.

module Meta_map : sig ... end

Associative containers with Heterogeneous Values

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 with_span : 
  ?__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.

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 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_sub_span : 
  parent:explicit_span ->
  ?flavor:[ `Sync | `Async ] ->
  ?__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.

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.

since 0.3

val enter_manual_toplevel_span : 
  ?flavor:[ `Sync | `Async ] ->
  ?__FUNCTION__:string ->
  __FILE__:string ->
  __LINE__:int ->
  ?data:(unit -> (string * user_data) list) ->
  string ->
  explicit_span

Like with_span but the caller is responsible for carrying this explicit_span around until it's exited with exit_manual_span. The span can be used as a parent in enter_manual_sub_span.

parameter flavor
see enter_manual_sub_span for more details.

since 0.3

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

val messagef : 
  ?span:span ->
  ?data:(unit -> (string * user_data) list) ->
  ((('a, 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.

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 : 
  ?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 data
metadata for this metric (since 0.4)

val counter_float : 
  ?data:(unit -> (string * user_data) list) ->
  string ->
  float ->
  unit

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

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 shutdown : unit -> unit

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

package trace

Tracing

Collector