mirror of https://github.com/python/cpython
373 lines
12 KiB
ReStructuredText
373 lines
12 KiB
ReStructuredText
:mod:`!sys.monitoring` --- Execution event monitoring
|
|
=====================================================
|
|
|
|
.. module:: sys.monitoring
|
|
:synopsis: Access and control event monitoring
|
|
|
|
.. versionadded:: 3.12
|
|
|
|
-----------------
|
|
|
|
.. note::
|
|
|
|
:mod:`sys.monitoring` is a namespace within the :mod:`sys` module,
|
|
not an independent module, so there is no need to
|
|
``import sys.monitoring``, simply ``import sys`` and then use
|
|
``sys.monitoring``.
|
|
|
|
|
|
This namespace provides access to the functions and constants necessary to
|
|
activate and control event monitoring.
|
|
|
|
As programs execute, events occur that might be of interest to tools that
|
|
monitor execution. The :mod:`sys.monitoring` namespace provides means to
|
|
receive callbacks when events of interest occur.
|
|
|
|
The monitoring API consists of three components:
|
|
|
|
* `Tool identifiers`_
|
|
* `Events`_
|
|
* :ref:`Callbacks <callbacks>`
|
|
|
|
Tool identifiers
|
|
----------------
|
|
|
|
A tool identifier is an integer and the associated name.
|
|
Tool identifiers are used to discourage tools from interfering with each
|
|
other and to allow multiple tools to operate at the same time.
|
|
Currently tools are completely independent and cannot be used to
|
|
monitor each other. This restriction may be lifted in the future.
|
|
|
|
Before registering or activating events, a tool should choose an identifier.
|
|
Identifiers are integers in the range 0 to 5 inclusive.
|
|
|
|
Registering and using tools
|
|
'''''''''''''''''''''''''''
|
|
|
|
.. function:: use_tool_id(tool_id: int, name: str, /) -> None
|
|
|
|
Must be called before *tool_id* can be used.
|
|
*tool_id* must be in the range 0 to 5 inclusive.
|
|
Raises a :exc:`ValueError` if *tool_id* is in use.
|
|
|
|
.. function:: free_tool_id(tool_id: int, /) -> None
|
|
|
|
Should be called once a tool no longer requires *tool_id*.
|
|
|
|
.. note::
|
|
|
|
:func:`free_tool_id` will not disable global or local events associated
|
|
with *tool_id*, nor will it unregister any callback functions. This
|
|
function is only intended to be used to notify the VM that the
|
|
particular *tool_id* is no longer in use.
|
|
|
|
.. function:: get_tool(tool_id: int, /) -> str | None
|
|
|
|
Returns the name of the tool if *tool_id* is in use,
|
|
otherwise it returns ``None``.
|
|
*tool_id* must be in the range 0 to 5 inclusive.
|
|
|
|
All IDs are treated the same by the VM with regard to events, but the
|
|
following IDs are pre-defined to make co-operation of tools easier::
|
|
|
|
sys.monitoring.DEBUGGER_ID = 0
|
|
sys.monitoring.COVERAGE_ID = 1
|
|
sys.monitoring.PROFILER_ID = 2
|
|
sys.monitoring.OPTIMIZER_ID = 5
|
|
|
|
|
|
Events
|
|
------
|
|
|
|
The following events are supported:
|
|
|
|
.. monitoring-event:: BRANCH
|
|
|
|
A conditional branch is taken (or not).
|
|
|
|
.. monitoring-event:: CALL
|
|
|
|
A call in Python code (event occurs before the call).
|
|
|
|
.. monitoring-event:: C_RAISE
|
|
|
|
An exception raised from any callable, except for Python functions (event occurs after the exit).
|
|
|
|
.. monitoring-event:: C_RETURN
|
|
|
|
Return from any callable, except for Python functions (event occurs after the return).
|
|
|
|
.. monitoring-event:: EXCEPTION_HANDLED
|
|
|
|
An exception is handled.
|
|
|
|
.. monitoring-event:: INSTRUCTION
|
|
|
|
A VM instruction is about to be executed.
|
|
|
|
.. monitoring-event:: JUMP
|
|
|
|
An unconditional jump in the control flow graph is made.
|
|
|
|
.. monitoring-event:: LINE
|
|
|
|
An instruction is about to be executed that has a different line number from the preceding instruction.
|
|
|
|
.. monitoring-event:: PY_RESUME
|
|
|
|
Resumption of a Python function (for generator and coroutine functions), except for ``throw()`` calls.
|
|
|
|
.. monitoring-event:: PY_RETURN
|
|
|
|
Return from a Python function (occurs immediately before the return, the callee's frame will be on the stack).
|
|
|
|
.. monitoring-event:: PY_START
|
|
|
|
Start of a Python function (occurs immediately after the call, the callee's frame will be on the stack)
|
|
|
|
.. monitoring-event:: PY_THROW
|
|
|
|
A Python function is resumed by a ``throw()`` call.
|
|
|
|
.. monitoring-event:: PY_UNWIND
|
|
|
|
Exit from a Python function during exception unwinding.
|
|
|
|
.. monitoring-event:: PY_YIELD
|
|
|
|
Yield from a Python function (occurs immediately before the yield, the callee's frame will be on the stack).
|
|
|
|
.. monitoring-event:: RAISE
|
|
|
|
An exception is raised, except those that cause a :monitoring-event:`STOP_ITERATION` event.
|
|
|
|
.. monitoring-event:: RERAISE
|
|
|
|
An exception is re-raised, for example at the end of a :keyword:`finally` block.
|
|
|
|
.. monitoring-event:: STOP_ITERATION
|
|
|
|
An artificial :exc:`StopIteration` is raised; see `the STOP_ITERATION event`_.
|
|
|
|
|
|
More events may be added in the future.
|
|
|
|
These events are attributes of the :mod:`!sys.monitoring.events` namespace.
|
|
Each event is represented as a power-of-2 integer constant.
|
|
To define a set of events, simply bitwise or the individual events together.
|
|
For example, to specify both :monitoring-event:`PY_RETURN` and :monitoring-event:`PY_START`
|
|
events, use the expression ``PY_RETURN | PY_START``.
|
|
|
|
.. monitoring-event:: NO_EVENTS
|
|
|
|
An alias for ``0`` so users can do explicit comparisons like::
|
|
|
|
if get_events(DEBUGGER_ID) == NO_EVENTS:
|
|
...
|
|
|
|
Events are divided into three groups:
|
|
|
|
Local events
|
|
''''''''''''
|
|
|
|
Local events are associated with normal execution of the program and happen
|
|
at clearly defined locations. All local events can be disabled.
|
|
The local events are:
|
|
|
|
* :monitoring-event:`PY_START`
|
|
* :monitoring-event:`PY_RESUME`
|
|
* :monitoring-event:`PY_RETURN`
|
|
* :monitoring-event:`PY_YIELD`
|
|
* :monitoring-event:`CALL`
|
|
* :monitoring-event:`LINE`
|
|
* :monitoring-event:`INSTRUCTION`
|
|
* :monitoring-event:`JUMP`
|
|
* :monitoring-event:`BRANCH`
|
|
* :monitoring-event:`STOP_ITERATION`
|
|
|
|
Ancillary events
|
|
''''''''''''''''
|
|
|
|
Ancillary events can be monitored like other events, but are controlled
|
|
by another event:
|
|
|
|
* :monitoring-event:`C_RAISE`
|
|
* :monitoring-event:`C_RETURN`
|
|
|
|
The :monitoring-event:`C_RETURN` and :monitoring-event:`C_RAISE` events
|
|
are controlled by the :monitoring-event:`CALL` event.
|
|
:monitoring-event:`C_RETURN` and :monitoring-event:`C_RAISE` events will only be seen if the
|
|
corresponding :monitoring-event:`CALL` event is being monitored.
|
|
|
|
Other events
|
|
''''''''''''
|
|
|
|
Other events are not necessarily tied to a specific location in the
|
|
program and cannot be individually disabled.
|
|
|
|
The other events that can be monitored are:
|
|
|
|
* :monitoring-event:`PY_THROW`
|
|
* :monitoring-event:`PY_UNWIND`
|
|
* :monitoring-event:`RAISE`
|
|
* :monitoring-event:`EXCEPTION_HANDLED`
|
|
|
|
|
|
The STOP_ITERATION event
|
|
''''''''''''''''''''''''
|
|
|
|
:pep:`PEP 380 <380#use-of-stopiteration-to-return-values>`
|
|
specifies that a :exc:`StopIteration` exception is raised when returning a value
|
|
from a generator or coroutine. However, this is a very inefficient way to
|
|
return a value, so some Python implementations, notably CPython 3.12+, do not
|
|
raise an exception unless it would be visible to other code.
|
|
|
|
To allow tools to monitor for real exceptions without slowing down generators
|
|
and coroutines, the :monitoring-event:`STOP_ITERATION` event is provided.
|
|
:monitoring-event:`STOP_ITERATION` can be locally disabled, unlike :monitoring-event:`RAISE`.
|
|
|
|
Note that the :monitoring-event:`STOP_ITERATION` event and the :monitoring-event:`RAISE`
|
|
event for a :exc:`StopIteration` exception are equivalent, and are treated as interchangeable
|
|
when generating events. Implementations will favor :monitoring-event:`STOP_ITERATION` for
|
|
performance reasons, but may generate a :monitoring-event:`RAISE` event with a :exc:`StopIteration`.
|
|
|
|
Turning events on and off
|
|
-------------------------
|
|
|
|
In order to monitor an event, it must be turned on and a corresponding callback
|
|
must be registered.
|
|
Events can be turned on or off by setting the events either globally or
|
|
for a particular code object.
|
|
|
|
|
|
Setting events globally
|
|
'''''''''''''''''''''''
|
|
|
|
Events can be controlled globally by modifying the set of events being monitored.
|
|
|
|
.. function:: get_events(tool_id: int, /) -> int
|
|
|
|
Returns the ``int`` representing all the active events.
|
|
|
|
.. function:: set_events(tool_id: int, event_set: int, /) -> None
|
|
|
|
Activates all events which are set in *event_set*.
|
|
Raises a :exc:`ValueError` if *tool_id* is not in use.
|
|
|
|
No events are active by default.
|
|
|
|
Per code object events
|
|
''''''''''''''''''''''
|
|
|
|
Events can also be controlled on a per code object basis. The functions
|
|
defined below which accept a :class:`types.CodeType` should be prepared
|
|
to accept a look-alike object from functions which are not defined
|
|
in Python (see :ref:`c-api-monitoring`).
|
|
|
|
.. function:: get_local_events(tool_id: int, code: CodeType, /) -> int
|
|
|
|
Returns all the local events for *code*
|
|
|
|
.. function:: set_local_events(tool_id: int, code: CodeType, event_set: int, /) -> None
|
|
|
|
Activates all the local events for *code* which are set in *event_set*.
|
|
Raises a :exc:`ValueError` if *tool_id* is not in use.
|
|
|
|
Local events add to global events, but do not mask them.
|
|
In other words, all global events will trigger for a code object,
|
|
regardless of the local events.
|
|
|
|
|
|
Disabling events
|
|
''''''''''''''''
|
|
|
|
.. data:: DISABLE
|
|
|
|
A special value that can be returned from a callback function to disable
|
|
events for the current code location.
|
|
|
|
Local events can be disabled for a specific code location by returning
|
|
:data:`sys.monitoring.DISABLE` from a callback function. This does not change
|
|
which events are set, or any other code locations for the same event.
|
|
|
|
Disabling events for specific locations is very important for high
|
|
performance monitoring. For example, a program can be run under a
|
|
debugger with no overhead if the debugger disables all monitoring
|
|
except for a few breakpoints.
|
|
|
|
.. function:: restart_events() -> None
|
|
|
|
Enable all the events that were disabled by :data:`sys.monitoring.DISABLE`
|
|
for all tools.
|
|
|
|
|
|
.. _callbacks:
|
|
|
|
Registering callback functions
|
|
------------------------------
|
|
|
|
To register a callable for events call
|
|
|
|
.. function:: register_callback(tool_id: int, event: int, func: Callable | None, /) -> Callable | None
|
|
|
|
Registers the callable *func* for the *event* with the given *tool_id*
|
|
|
|
If another callback was registered for the given *tool_id* and *event*,
|
|
it is unregistered and returned.
|
|
Otherwise :func:`register_callback` returns ``None``.
|
|
|
|
|
|
Functions can be unregistered by calling
|
|
``sys.monitoring.register_callback(tool_id, event, None)``.
|
|
|
|
Callback functions can be registered and unregistered at any time.
|
|
|
|
Registering or unregistering a callback function will generate a :func:`sys.audit` event.
|
|
|
|
|
|
Callback function arguments
|
|
'''''''''''''''''''''''''''
|
|
|
|
.. data:: MISSING
|
|
|
|
A special value that is passed to a callback function to indicate
|
|
that there are no arguments to the call.
|
|
|
|
When an active event occurs, the registered callback function is called.
|
|
Different events will provide the callback function with different arguments, as follows:
|
|
|
|
* :monitoring-event:`PY_START` and :monitoring-event:`PY_RESUME`::
|
|
|
|
func(code: CodeType, instruction_offset: int) -> DISABLE | Any
|
|
|
|
* :monitoring-event:`PY_RETURN` and :monitoring-event:`PY_YIELD`::
|
|
|
|
func(code: CodeType, instruction_offset: int, retval: object) -> DISABLE | Any
|
|
|
|
* :monitoring-event:`CALL`, :monitoring-event:`C_RAISE` and :monitoring-event:`C_RETURN`::
|
|
|
|
func(code: CodeType, instruction_offset: int, callable: object, arg0: object | MISSING) -> DISABLE | Any
|
|
|
|
If there are no arguments, *arg0* is set to :data:`sys.monitoring.MISSING`.
|
|
|
|
* :monitoring-event:`RAISE`, :monitoring-event:`RERAISE`, :monitoring-event:`EXCEPTION_HANDLED`,
|
|
:monitoring-event:`PY_UNWIND`, :monitoring-event:`PY_THROW` and :monitoring-event:`STOP_ITERATION`::
|
|
|
|
func(code: CodeType, instruction_offset: int, exception: BaseException) -> DISABLE | Any
|
|
|
|
* :monitoring-event:`LINE`::
|
|
|
|
func(code: CodeType, line_number: int) -> DISABLE | Any
|
|
|
|
* :monitoring-event:`BRANCH` and :monitoring-event:`JUMP`::
|
|
|
|
func(code: CodeType, instruction_offset: int, destination_offset: int) -> DISABLE | Any
|
|
|
|
Note that the *destination_offset* is where the code will next execute.
|
|
For an untaken branch this will be the offset of the instruction following
|
|
the branch.
|
|
|
|
* :monitoring-event:`INSTRUCTION`::
|
|
|
|
func(code: CodeType, instruction_offset: int) -> DISABLE | Any
|