gh-118692: Avoid creating unnecessary StopIteration instances for monitoring

Doc/c-api/monitoring.rst

@@ -121,10 +121,10 @@ See :mod:`sys.monitoring` for descriptions of the events.
  :c:func:`PyErr_GetRaisedException`).
 
 
-.. c:function:: int PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset)
+.. c:function:: int PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset, PyObject *value)
 
- Fire a ``STOP_ITERATION`` event with the current exception (as returned by
-:c:func:`PyErr_GetRaisedException`).
+ Fire a ``STOP_ITERATION`` event. If ``value`` is an instance of :exc:`StopIteration`, it is used. Otherwise,
+a new :exc:`StopIteration` instance is created with ``value`` as its argument.
 
 
 Managing the Monitoring State

Include/cpython/monitoring.h

@@ -101,7 +101,7 @@ PyAPI_FUNC(int)
 _PyMonitoring_FirePyUnwindEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset);
 
 PyAPI_FUNC(int)
-_PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset);
+_PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset, PyObject *value);
 
 
 #define _PYMONITORING_IF_ACTIVE(STATE, X) \
@@ -240,11 +240,11 @@ PyMonitoring_FirePyUnwindEvent(PyMonitoringState *state, PyObject *codelike, int
 }
 
 static inline int
-PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset)
+PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset, PyObject *value)
 {
  _PYMONITORING_IF_ACTIVE(
  state,
- _PyMonitoring_FireStopIterationEvent(state, codelike, offset));
+ _PyMonitoring_FireStopIterationEvent(state, codelike, offset, value));
 }
 
 #undef _PYMONITORING_IF_ACTIVE

Lib/test/test_monitoring.py

@@ -1938,19 +1938,28 @@ def setUp(self):
  ( 1, E.RAISE, capi.fire_event_raise, ValueError(2)),
  ( 1, E.EXCEPTION_HANDLED, capi.fire_event_exception_handled, ValueError(5)),
  ( 1, E.PY_UNWIND, capi.fire_event_py_unwind, ValueError(6)),
- ( 1, E.STOP_ITERATION, capi.fire_event_stop_iteration, ValueError(7)),
+ ( 1, E.STOP_ITERATION, capi.fire_event_stop_iteration, 7),
+ ( 1, E.STOP_ITERATION, capi.fire_event_stop_iteration, StopIteration(8)),
  ]
 
+ self.EXPECT_RAISED_EXCEPTION = [E.PY_THROW, E.RAISE, E.EXCEPTION_HANDLED, E.PY_UNWIND]
 
- def check_event_count(self, event, func, args, expected):
+
+ def check_event_count(self, event, func, args, expected, callback_raises=None):
  class Counter:
- def __init__(self):
+ def __init__(self, callback_raises):
+ self.callback_raises = callback_raises
  self.count = 0
+
  def __call__(self, *args):
  self.count += 1
+ if self.callback_raises:
+ exc = self.callback_raises
+ self.callback_raises = None
+ raise exc
 
  try:
- counter = Counter()
+ counter = Counter(callback_raises)
  sys.monitoring.register_callback(TEST_TOOL, event, counter)
  if event == E.C_RETURN or event == E.C_RAISE:
  sys.monitoring.set_events(TEST_TOOL, E.CALL)
@@ -1987,8 +1996,9 @@ def test_fire_event(self):
 
  def test_missing_exception(self):
  for _, event, function, *args in self.cases:
- if not (args and isinstance(args[-1], BaseException)):
+ if event not in self.EXPECT_RAISED_EXCEPTION:
  continue
+ assert args and isinstance(args[-1], BaseException)
  offset = 0
  self.codelike = _testcapi.CodeLike(1)
  with self.subTest(function.__name__):
@@ -1997,6 +2007,17 @@ def test_missing_exception(self):
  expected = ValueError(f"Firing event{evt} with no exception set")
  self.check_event_count(event, function, args_, expected)
 
+ def test_fire_event_failing_callback(self):
+ for expected, event, function, *args in self.cases:
+ offset = 0
+ self.codelike = _testcapi.CodeLike(1)
+ with self.subTest(function.__name__):
+ args_ = (self.codelike, offset) + tuple(args)
+ exc = OSError(42)
+ with self.assertRaises(type(exc)):
+ self.check_event_count(event, function, args_, expected,
+ callback_raises=exc)
+
 
  CANNOT_DISABLE ={E.PY_THROW, E.RAISE, E.RERAISE,
  E.EXCEPTION_HANDLED, E.PY_UNWIND }

Misc/NEWS.d/next/Core and Builtins/2024-05-20-14-57-39.gh-issue-118692.Qadm7F.rst

@@ -0,0 +1 @@
+Avoid creating unnecessary :exc:`StopIteration` instances for monitoring.

Modules/_testcapi/monitoring.c

@@ -416,16 +416,17 @@ fire_event_stop_iteration(PyObject *self, PyObject *args)
 {
  PyObject *codelike;
  int offset;
- PyObject *exception;
- if (!PyArg_ParseTuple(args, "OiO", &codelike, &offset, &exception)){
+ PyObject *value;
+ if (!PyArg_ParseTuple(args, "OiO", &codelike, &offset, &value)){
  return NULL;
  }
- NULLABLE(exception);
+ NULLABLE(value);
+ PyObject *exception = NULL;
  PyMonitoringState *state = setup_fire(codelike, offset, exception);
  if (state == NULL){
  return NULL;
  }
- int res = PyMonitoring_FireStopIterationEvent(state, codelike, offset);
+ int res = PyMonitoring_FireStopIterationEvent(state, codelike, offset, value);
  RETURN_INT(teardown_fire(res, state, exception));
 }
 

Python/bytecodes.c

@@ -292,11 +292,9 @@ dummy_func(
  /* Need to create a fake StopIteration error here,
  * to conform to PEP 380 */
  if (PyGen_Check(receiver)){
- PyErr_SetObject(PyExc_StopIteration, value);
- if (monitor_stop_iteration(tstate, frame, this_instr)){
+ if (monitor_stop_iteration(tstate, frame, this_instr, value)){
  ERROR_NO_POP();
  }
- PyErr_SetRaisedException(NULL);
  }
  DECREF_INPUTS();
  }
@@ -307,11 +305,9 @@ dummy_func(
 
  tier1 inst(INSTRUMENTED_END_SEND, (receiver, value -- value)){
  if (PyGen_Check(receiver) || PyCoro_CheckExact(receiver)){
- PyErr_SetObject(PyExc_StopIteration, value);
- if (monitor_stop_iteration(tstate, frame, this_instr)){
+ if (monitor_stop_iteration(tstate, frame, this_instr, value)){
  ERROR_NO_POP();
  }
- PyErr_SetRaisedException(NULL);
  }
  Py_DECREF(receiver);
  }

Python/ceval.c

@@ -231,7 +231,8 @@ static void monitor_reraise(PyThreadState *tstate,
  _Py_CODEUNIT *instr);
 static int monitor_stop_iteration(PyThreadState *tstate,
  _PyInterpreterFrame *frame,
- _Py_CODEUNIT *instr);
+ _Py_CODEUNIT *instr,
+ PyObject *value);
 static void monitor_unwind(PyThreadState *tstate,
  _PyInterpreterFrame *frame,
  _Py_CODEUNIT *instr);
@@ -2215,12 +2216,19 @@ monitor_reraise(PyThreadState *tstate, _PyInterpreterFrame *frame,
 
 static int
 monitor_stop_iteration(PyThreadState *tstate, _PyInterpreterFrame *frame,
- _Py_CODEUNIT *instr)
+ _Py_CODEUNIT *instr, PyObject *value)
 {
  if (no_tools_for_local_event(tstate, frame, PY_MONITORING_EVENT_STOP_ITERATION)){
  return 0;
  }
- return do_monitor_exc(tstate, frame, instr, PY_MONITORING_EVENT_STOP_ITERATION);
+ assert(!PyErr_Occurred());
+ PyErr_SetObject(PyExc_StopIteration, value);
+ int res = do_monitor_exc(tstate, frame, instr, PY_MONITORING_EVENT_STOP_ITERATION);
+ if (res < 0){
+ return res;
+ }
+ PyErr_SetRaisedException(NULL);
+ return 0;
 }
 
 static void

Python/instrumentation.c

@@ -2622,7 +2622,7 @@ exception_event_teardown(int err, PyObject *exc){
  }
  else{
  assert(PyErr_Occurred());
-Py_DECREF(exc);
+Py_XDECREF(exc);
  }
  return err;
 }
@@ -2712,15 +2712,17 @@ _PyMonitoring_FirePyUnwindEvent(PyMonitoringState *state, PyObject *codelike, in
 }
 
 int
-_PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset)
+_PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset, PyObject *value)
 {
  int event = PY_MONITORING_EVENT_STOP_ITERATION;
  assert(state->active);
+ assert(!PyErr_Occurred());
+ PyErr_SetObject(PyExc_StopIteration, value);
  PyObject *exc;
  if (exception_event_setup(&exc, event) < 0){
  return -1;
  }
  PyObject *args[4] ={NULL, NULL, NULL, exc };
  int err = capi_call_instrumentation(state, codelike, offset, args, 3, event);
- return exception_event_teardown(err, exc);
+ return exception_event_teardown(err, NULL);
 }