Monitoring C API#

Added in version 3.13.

An extension may need to interact with the event monitoring system. Subscribing to events and registering callbacks can be done via the Python API exposed in "sys.monitoring".

Generating Execution Events#

The functions below make it possible for an extension to fire monitoring events as it emulates the execution of Python code. Each of these functions accepts a "PyMonitoringState" struct which contains concise information about the activation state of events, as well as the event arguments, which include a "PyObject*" representing the code object, the instruction offset and sometimes additional, event- specific arguments (see "sys.monitoring" for details about the signatures of the different event callbacks). The "codelike" argument should be an instance of "types.CodeType" or of a type that emulates it.

The VM disables tracing when firing an event, so there is no need for user code to do that.

Monitoring functions should not be called with an exception set, except those listed below as working with the current exception.

type PyMonitoringState

Representation of the state of an event type. It is allocated by the user while its contents are maintained by the monitoring API functions described below.

All of the functions below return 0 on success and -1 (with an exception set) on error.

See "sys.monitoring" for descriptions of the events.

int PyMonitoring_FirePyStartEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "PY_START" event.

int PyMonitoring_FirePyResumeEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "PY_RESUME" event.

int PyMonitoring_FirePyReturnEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *retval)

Fire a "PY_RETURN" event.

int PyMonitoring_FirePyYieldEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *retval)

Fire a "PY_YIELD" event.

int PyMonitoring_FireCallEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject callable, PyObject arg0)

Fire a "CALL" event.

int PyMonitoring_FireLineEvent(PyMonitoringState state, PyObject codelike, int32_t offset, int lineno)

Fire a "LINE" event.

int PyMonitoring_FireJumpEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *target_offset)

Fire a "JUMP" event.

int PyMonitoring_FireBranchLeftEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *target_offset)

Fire a "BRANCH_LEFT" event.

int PyMonitoring_FireBranchRightEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *target_offset)

Fire a "BRANCH_RIGHT" event.

int PyMonitoring_FireCReturnEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *retval)

Fire a "C_RETURN" event.

int PyMonitoring_FirePyThrowEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "PY_THROW" event with the current exception (as returned by "PyErr_GetRaisedException()").

int PyMonitoring_FireRaiseEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "RAISE" event with the current exception (as returned by "PyErr_GetRaisedException()").

int PyMonitoring_FireCRaiseEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "C_RAISE" event with the current exception (as returned by "PyErr_GetRaisedException()").

int PyMonitoring_FireReraiseEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "RERAISE" event with the current exception (as returned by "PyErr_GetRaisedException()").

int PyMonitoring_FireExceptionHandledEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire an "EXCEPTION_HANDLED" event with the current exception (as returned by "PyErr_GetRaisedException()").

int PyMonitoring_FirePyUnwindEvent(PyMonitoringState state, PyObject codelike, int32_t offset)

Fire a "PY_UNWIND" event with the current exception (as returned by "PyErr_GetRaisedException()").

int PyMonitoring_FireStopIterationEvent(PyMonitoringState state, PyObject codelike, int32_t offset, PyObject *value)

Fire a "STOP_ITERATION" event. If "value" is an instance of "StopIteration", it is used. Otherwise, a new "StopIteration" instance is created with "value" as its argument.

Managing the Monitoring State#

Monitoring states can be managed with the help of monitoring scopes. A scope would typically correspond to a Python function.

int PyMonitoring_EnterScope(PyMonitoringState state_array, uint64_t version, const uint8_t *event_types, Py_ssize_t length)

Enter a monitored scope. "event_types" is an array of the event IDs for events that may be fired from the scope. For example, the ID of a "PY_START" event is the value "PY_MONITORING_EVENT_PY_START", which is numerically equal to the base-2 logarithm of "sys.monitoring.events.PY_START". "state_array" is an array with a monitoring state entry for each event in "event_types", it is allocated by the user but populated by "PyMonitoring_EnterScope()" with information about the activation state of the event. The size of "event_types" (and hence also of "state_array") is given in "length".

The "version" argument is a pointer to a value which should be allocated by the user together with "state_array" and initialized to 0, and then set only by "PyMonitoring_EnterScope()" itself. It allows this function to determine whether event states have changed since the previous call, and to return quickly if they have not.

The scopes referred to here are lexical scopes: a function, class or method. "PyMonitoring_EnterScope()" should be called whenever the lexical scope is entered. Scopes can be reentered, reusing the same state_array and version, in situations like when emulating a recursive Python function. When a code-like's execution is paused, such as when emulating a generator, the scope needs to be exited and re-entered.

The macros for event_types are:

+----------------------------------------------------+---------------------------------------+ | Macro | Event | |====================================================|=======================================| | PY_MONITORING_EVENT_BRANCH_LEFT | "BRANCH_LEFT" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_BRANCH_RIGHT | "BRANCH_RIGHT" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_CALL | "CALL" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_C_RAISE | "C_RAISE" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_C_RETURN | "C_RETURN" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_EXCEPTION_HANDLED | "EXCEPTION_HANDLED" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_INSTRUCTION | "INSTRUCTION" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_JUMP | "JUMP" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_LINE | "LINE" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_PY_RESUME | "PY_RESUME" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_PY_RETURN | "PY_RETURN" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_PY_START | "PY_START" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_PY_THROW | "PY_THROW" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_PY_UNWIND | "PY_UNWIND" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_PY_YIELD | "PY_YIELD" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_RAISE | "RAISE" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_RERAISE | "RERAISE" | +----------------------------------------------------+---------------------------------------+ | PY_MONITORING_EVENT_STOP_ITERATION | "STOP_ITERATION" | +----------------------------------------------------+---------------------------------------+

int PyMonitoring_ExitScope(void)

Exit the last scope that was entered with "PyMonitoring_EnterScope()".

int PY_MONITORING_IS_INSTRUMENTED_EVENT(uint8_t ev)

Return true if the event corresponding to the event ID ev is a local event.

Added in version 3.13.

Soft deprecated since version 3.14.