tracing v0.15.0 · OCaml Package

module type Destination = sig ... end

See docs in Writer_intf for what this is for

val create : 
  ?num_temp_strs:int ->
  destination:(module Destination) ->
  unit ->
  t

val set_string_slot : t -> slot:int -> string -> String_id.t

Interns a string directly to the specified slot (whereas set_temp_string_slot may shift the index since certain indices are reserved for internal use). Will raise when setting a slot that is not a temp string slot or when setting slot 1 to any string other than "process".

Useful for preserving the string ID usage of parsed traces in a way that can lead to exact byte equality after a round trip through parsing and writing.

val force_switch_buffers : t -> unit

Immediately ask the destination for a new buffer even if the current one isn't full. This is intended for use by the probe infrastructure when a destination for the global writer is initialized.

val flush_and_notify : t -> unit

Finish all pending writes to underlying buffer and notify the Destination

This is currently only intended for use by tests.

type header

module Event_type : sig ... end

For use with precompute_header_and_size

val precompute_header : 
  event_type:Event_type.t ->
  extra_words:int ->
  arg_types:Arg_types.t ->
  thread:Thread_id.t ->
  category:String_id.t ->
  name:String_id.t ->
  header

Pre-compose an event header word, for use with write_from_header_with_tsc

val write_from_header_with_tsc : t -> header:header -> unit

Write an event using a pre-composed header, and using less safety checking than the normal event writing functions, intended for low-overhead probe instrumentation. Also uses the rdtsc counter for the ticks field, meaning this Writer must have been created with a calibrated ticks_per_second field to have correct timing.

The pre-composition itself saves about 3ns per event. The omission of unnecessary checks saves additional time. Overall in benchmarks this is about 2x faster than using the usual write_* functions, saving about 6ns per event.

The only caller-visible check omission should be that it doesn't check the corectness of arguments, which can result in invalid trace files if the arguments written don't match the header. Users of this function must use Write_arg_unchecked because it doesn't set the necessary state for checking.

val write_from_header_and_get_tsc : t -> header:header -> Time_stamp_counter.t

Same as write_from_header_with_tsc but but returns ticks. See Tracing.Writer.write_duration_instant.

val write_tsc : t -> Time_stamp_counter.t -> unit

Unchecked writing of the result of write_from_header_and_get_tsc after the arguments.

module Write_arg_unchecked : sig ... end

Unchecked versions of the Write_arg functions that can result in invalid traces.

package tracing