Module Runtime_events

module Runtime_events: sig .. end

Runtime events - ring buffer-based runtime tracing

This module enables users to enable and subscribe to tracing events from the Garbage Collector and other parts of the OCaml runtime. This can be useful for diagnostic or performance monitoring purposes. This module can be used to subscribe to events for the current process or external processes asynchronously.

When enabled (either via setting the OCAML_RUNTIME_EVENTS_START environment variable or calling Runtime_events.start) a file with the pid of the process and extension .events will be created. By default this is in the current directory but can be over-ridden by the OCAML_RUNTIME_EVENTS_DIR environment variable. Each domain maintains its own ring buffer in a section of the larger file into which it emits events.

There is additionally a set of C APIs in runtime_events.h that can enable zero-impact monitoring of the current process or bindings for other languages.

The runtime events system's behaviour can be controlled by the following environment variables:

  • OCAML_RUNTIME_EVENTS_START if set will cause the runtime events system to be started as part of the OCaml runtime initialization.
  • OCAML_RUNTIME_EVENTS_DIR sets the directory where the runtime events ring buffers will be located. If not present the program's working directory will be used.
  • OCAML_RUNTIME_EVENTS_PRESERVE if set will prevent the OCaml runtime from removing its ring buffers when it terminates. This can help if monitoring very short running programs.
type runtime_counter =
| EV_C_FORCE_MINOR_ALLOC_SMALL
| EV_C_FORCE_MINOR_MAKE_VECT
| EV_C_FORCE_MINOR_SET_MINOR_HEAP_SIZE
| EV_C_FORCE_MINOR_MEMPROF
| EV_C_MINOR_PROMOTED
| EV_C_MINOR_ALLOCATED
| EV_C_REQUEST_MAJOR_ALLOC_SHR
| EV_C_REQUEST_MAJOR_ADJUST_GC_SPEED
| EV_C_REQUEST_MINOR_REALLOC_REF_TABLE
| EV_C_REQUEST_MINOR_REALLOC_EPHE_REF_TABLE
| EV_C_REQUEST_MINOR_REALLOC_CUSTOM_TABLE

The type for counter events emitted by the runtime

type runtime_phase =
| EV_EXPLICIT_GC_SET
| EV_EXPLICIT_GC_STAT
| EV_EXPLICIT_GC_MINOR
| EV_EXPLICIT_GC_MAJOR
| EV_EXPLICIT_GC_FULL_MAJOR
| EV_EXPLICIT_GC_COMPACT
| EV_MAJOR
| EV_MAJOR_SWEEP
| EV_MAJOR_MARK_ROOTS
| EV_MAJOR_MARK
| EV_MINOR
| EV_MINOR_LOCAL_ROOTS
| EV_MINOR_FINALIZED
| EV_EXPLICIT_GC_MAJOR_SLICE
| EV_FINALISE_UPDATE_FIRST
| EV_FINALISE_UPDATE_LAST
| EV_INTERRUPT_REMOTE
| EV_MAJOR_EPHE_MARK
| EV_MAJOR_EPHE_SWEEP
| EV_MAJOR_FINISH_MARKING
| EV_MAJOR_GC_CYCLE_DOMAINS
| EV_MAJOR_GC_PHASE_CHANGE
| EV_MAJOR_GC_STW
| EV_MAJOR_MARK_OPPORTUNISTIC
| EV_MAJOR_SLICE
| EV_MAJOR_FINISH_CYCLE
| EV_MINOR_CLEAR
| EV_MINOR_FINALIZERS_OLDIFY
| EV_MINOR_GLOBAL_ROOTS
| EV_MINOR_LEAVE_BARRIER
| EV_STW_API_BARRIER
| EV_STW_HANDLER
| EV_STW_LEADER
| EV_MAJOR_FINISH_SWEEPING
| EV_MINOR_FINALIZERS_ADMIN
| EV_MINOR_REMEMBERED_SET
| EV_MINOR_REMEMBERED_SET_PROMOTE
| EV_MINOR_LOCAL_ROOTS_PROMOTE
| EV_DOMAIN_CONDITION_WAIT
| EV_DOMAIN_RESIZE_HEAP_RESERVATION

The type for span events emitted by the runtime

type lifecycle =
| EV_RING_START
| EV_RING_STOP
| EV_RING_PAUSE
| EV_RING_RESUME
| EV_FORK_PARENT
| EV_FORK_CHILD
| EV_DOMAIN_SPAWN
| EV_DOMAIN_TERMINATE

Lifecycle events for the ring itself

val lifecycle_name : lifecycle -> string

Return a string representation of a given lifecycle event type

val runtime_phase_name : runtime_phase -> string

Return a string representation of a given runtime phase event type

val runtime_counter_name : runtime_counter -> string

Return a string representation of a given runtime counter type

type cursor

Type of the cursor used when consuming

module Timestamp: sig .. end
module Callbacks: sig .. end
val start : unit -> unit

start () will start the collection of events in the runtime if not already started.

Events can be consumed by creating a cursor with create_cursor and providing a set of callbacks to be called for each type of event.

val pause : unit -> unit

pause () will pause the collection of events in the runtime. Traces are collected if the program has called Runtime_events.start () or the OCAML_RUNTIME_EVENTS_START environment variable has been set.

val resume : unit -> unit

resume () will resume the collection of events in the runtime. Traces are collected if the program has called Runtime_events.start () or the OCAML_RUNTIME_EVENTS_START environment variable has been set.

val create_cursor : (string * int) option -> cursor

create_cursor path_pid creates a cursor to read from an runtime_events. Cursors can be created for runtime_events in and out of process. A runtime_events ring-buffer may have multiple cursors reading from it at any point in time and a program may have multiple cursors open concurrently (for example if multiple consumers want different sets of events). If path_pid is None then a cursor is created for the current process. Otherwise the pair contains a string path to the directory that contains the pid.events file and int pid for the runtime_events of an external process to monitor.

val free_cursor : cursor -> unit

Free a previously created runtime_events cursor

val read_poll : cursor -> Callbacks.t -> int option -> int

read_poll cursor callbacks max_option calls the corresponding functions on callbacks for up to max_option events read off cursor's runtime_events and returns the number of events read.