# Module Runtime_events.Callbacks

    module Callbacks: sig .. end

    type t

Type of callbacks.

    val create : ?runtime_begin:(int ->
                           Runtime_events.Timestamp.t ->
                           Runtime_events.runtime_phase -> unit) ->
           ?runtime_end:(int ->
                         Runtime_events.Timestamp.t ->
                         Runtime_events.runtime_phase -> unit) ->
           ?runtime_counter:(int ->
                             Runtime_events.Timestamp.t ->
                             Runtime_events.runtime_counter -> int -> unit) ->
           ?alloc:(int -> Runtime_events.Timestamp.t -> int array -> unit) ->
           ?lifecycle:(int ->
                       Runtime_events.Timestamp.t ->
                       Runtime_events.lifecycle -> int option -> unit) ->
           ?lost_events:(int -> int -> unit) -> unit -> t

Create a `Callback` that optionally subscribes to one or more runtime events. The first int supplied to callbacks is the ring buffer index. Each domain owns a single ring buffer for the duration of the domain's existence. After a domain terminates, a newly spawned domain may take ownership of the ring buffer. A `runtime_begin` callback is called when the runtime enters a new phase (e.g a runtime_begin with EV_MINOR is called at the start of a minor GC). A `runtime_end` callback is called when the runtime leaves a certain phase. The `runtime_counter` callback is called when a counter is emitted by the runtime. `lifecycle` callbacks are called when the ring undergoes a change in lifecycle and a consumer may need to respond. `alloc` callbacks are currently only called on the instrumented runtime. `lost_events` callbacks are called if the consumer code detects some unconsumed events have been overwritten.

    val add_user_event : 'a Runtime_events.Type.t ->
           (int -> Runtime_events.Timestamp.t -> 'a Runtime_events.User.t -> 'a -> unit) ->
           t -> t

`add_user_event ty callback t` extends `t` to additionally subscribe to user events of type `ty`. When such an event happens, `callback` is called with the corresponding event and payload.