Runtime_eventsRuntime 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:
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| EV_C_MAJOR_HEAP_POOL_WORDSTotal words in a Domain's major heap pools. This is the sum of unallocated and live words in each pool.
*)| EV_C_MAJOR_HEAP_POOL_LIVE_WORDSCurrent live words in a Domain's major heap pools.
*)| EV_C_MAJOR_HEAP_LARGE_WORDSTotal words of a Domain's major heap large allocations. A large allocation is an allocation larger than the largest sized pool.
*)| EV_C_MAJOR_HEAP_POOL_FRAG_WORDSWords in a Domain's major heap pools lost to fragmentation. This is due to there not being a pool with the exact size of an allocation and a larger sized pool needing to be used.
*)| EV_C_MAJOR_HEAP_POOL_LIVE_BLOCKSLive blocks of a Domain's major heap pools.
*)| EV_C_MAJOR_HEAP_LARGE_BLOCKSLive blocks of a Domain's major heap large allocations.
*)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_RESERVATIONThe type for span events emitted by the runtime
val lifecycle_name : lifecycle -> stringReturn a string representation of a given lifecycle event type
val runtime_phase_name : runtime_phase -> stringReturn a string representation of a given runtime phase event type
val runtime_counter_name : runtime_counter -> stringReturn a string representation of a given runtime counter type
module Timestamp : sig ... endmodule Type : sig ... endmodule User : sig ... endUser events is a way for libraries to provide runtime events that can be consumed by other tools. These events can carry known data types or custom values. The current maximum number of user events is 8192.
module Callbacks : sig ... endstart () 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.
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.
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 -> cursorcreate_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 -> unitFree a previously created runtime_events cursor
val read_poll : cursor -> Callbacks.t -> int option -> intread_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.