bpo-31033: Improve the traceback for cancelled asyncio tasks (GH-19951)

When an asyncio.Task is cancelled, the exception traceback now
starts with where the task was first interrupted.  Previously,
the traceback only had "depth one."

10 files changed, 291 insertions, 81 deletions

diff --git a/Include/internal/pycore_pyerrors.h b/Include/internal/pycore_pyerrors.h
index bae1056..3290a37 100644
--- a/Include/internal/pycore_pyerrors.h
+++ b/Include/internal/pycore_pyerrors.h
@@ -14,6 +14,20 @@ static inline PyObject* _PyErr_Occurred(PyThreadState *tstate)
     return tstate->curexc_type;
 }
 
+static inline void _PyErr_ClearExcState(_PyErr_StackItem *exc_state)
+{
+    PyObject *t, *v, *tb;
+    t = exc_state->exc_type;
+    v = exc_state->exc_value;
+    tb = exc_state->exc_traceback;
+    exc_state->exc_type = NULL;
+    exc_state->exc_value = NULL;
+    exc_state->exc_traceback = NULL;
+    Py_XDECREF(t);
+    Py_XDECREF(v);
+    Py_XDECREF(tb);
+}
+
 
 PyAPI_FUNC(void) _PyErr_Fetch(
     PyThreadState *tstate,
@@ -36,6 +50,9 @@ PyAPI_FUNC(void) _PyErr_SetObject(
     PyObject *type,
     PyObject *value);
 
+PyAPI_FUNC(void) _PyErr_ChainStackItem(
+    _PyErr_StackItem *exc_state);
+
 PyAPI_FUNC(void) _PyErr_Clear(PyThreadState *tstate);
 
 PyAPI_FUNC(void) _PyErr_SetNone(PyThreadState *tstate, PyObject *exception);
diff --git a/Lib/asyncio/futures.py b/Lib/asyncio/futures.py
index 889f3e6..bed4da5 100644
--- a/Lib/asyncio/futures.py
+++ b/Lib/asyncio/futures.py
@@ -52,6 +52,8 @@ class Future:
     _loop = None
     _source_traceback = None
     _cancel_message = None
+    # A saved CancelledError for later chaining as an exception context.
+    _cancelled_exc = None
 
     # This field is used for a dual purpose:
     # - Its presence is a marker to declare that a class implements
@@ -124,6 +126,21 @@ class Future:
             raise RuntimeError("Future object is not initialized.")
         return loop
 
+    def _make_cancelled_error(self):
+        """Create the CancelledError to raise if the Future is cancelled.
+
+        This should only be called once when handling a cancellation since
+        it erases the saved context exception value.
+        """
+        if self._cancel_message is None:
+            exc = exceptions.CancelledError()
+        else:
+            exc = exceptions.CancelledError(self._cancel_message)
+        exc.__context__ = self._cancelled_exc
+        # Remove the reference since we don't need this anymore.
+        self._cancelled_exc = None
+        return exc
+
     def cancel(self, msg=None):
         """Cancel the future and schedule callbacks.
 
@@ -175,9 +192,8 @@ class Future:
         the future is done and has an exception set, this exception is raised.
         """
         if self._state == _CANCELLED:
-            raise exceptions.CancelledError(
-                '' if self._cancel_message is None else self._cancel_message)
-
+            exc = self._make_cancelled_error()
+            raise exc
         if self._state != _FINISHED:
             raise exceptions.InvalidStateError('Result is not ready.')
         self.__log_traceback = False
@@ -194,8 +210,8 @@ class Future:
         InvalidStateError.
         """
         if self._state == _CANCELLED:
-            raise exceptions.CancelledError(
-                '' if self._cancel_message is None else self._cancel_message)
+            exc = self._make_cancelled_error()
+            raise exc
         if self._state != _FINISHED:
             raise exceptions.InvalidStateError('Exception is not set.')
         self.__log_traceback = False
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index a3a0a33..21b98b6 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -270,8 +270,7 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
                 f'_step(): already done: {self!r}, {exc!r}')
         if self._must_cancel:
             if not isinstance(exc, exceptions.CancelledError):
-                exc = exceptions.CancelledError(''
-                    if self._cancel_message is None else self._cancel_message)
+                exc = self._make_cancelled_error()
             self._must_cancel = False
         coro = self._coro
         self._fut_waiter = None
@@ -293,11 +292,9 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
             else:
                 super().set_result(exc.value)
         except exceptions.CancelledError as exc:
-            if exc.args:
-                cancel_msg = exc.args[0]
-            else:
-                cancel_msg = None
-            super().cancel(msg=cancel_msg)  # I.e., Future.cancel(self).
+            # Save the original exception so we can chain it later.
+            self._cancelled_exc = exc
+            super().cancel()  # I.e., Future.cancel(self).
         except (KeyboardInterrupt, SystemExit) as exc:
             super().set_exception(exc)
             raise
@@ -787,8 +784,7 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
                 # Check if 'fut' is cancelled first, as
                 # 'fut.exception()' will *raise* a CancelledError
                 # instead of returning it.
-                exc = exceptions.CancelledError(''
-                    if fut._cancel_message is None else fut._cancel_message)
+                exc = fut._make_cancelled_error()
                 outer.set_exception(exc)
                 return
             else:
@@ -804,9 +800,12 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
 
             for fut in children:
                 if fut.cancelled():
-                    # Check if 'fut' is cancelled first, as
-                    # 'fut.exception()' will *raise* a CancelledError
-                    # instead of returning it.
+                    # Check if 'fut' is cancelled first, as 'fut.exception()'
+                    # will *raise* a CancelledError instead of returning it.
+                    # Also, since we're adding the exception return value
+                    # to 'results' instead of raising it, don't bother
+                    # setting __context__.  This also lets us preserve
+                    # calling '_make_cancelled_error()' at most once.
                     res = exceptions.CancelledError(
                         '' if fut._cancel_message is None else
                         fut._cancel_message)
@@ -820,8 +819,7 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
                 # If gather is being cancelled we must propagate the
                 # cancellation regardless of *return_exceptions* argument.
                 # See issue 32684.
-                exc = exceptions.CancelledError(''
-                    if fut._cancel_message is None else fut._cancel_message)
+                exc = fut._make_cancelled_error()
                 outer.set_exception(exc)
             else:
                 outer.set_result(results)
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index 65bee52..63968e2 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -10,6 +10,7 @@ import random
 import re
 import sys
 import textwrap
+import traceback
 import types
 import unittest
 import weakref
@@ -57,6 +58,22 @@ def format_coroutine(qualname, state, src, source_traceback, generator=False):
         return 'coro=<%s() %s at %s>' % (qualname, state, src)
 
 
+def get_innermost_context(exc):
+    """
+    Return information about the innermost exception context in the chain.
+    """
+    depth = 0
+    while True:
+        context = exc.__context__
+        if context is None:
+            break
+
+        exc = context
+        depth += 1
+
+    return (type(exc), exc.args, depth)
+
+
 class Dummy:
 
     def __repr__(self):
@@ -111,9 +128,10 @@ class BaseTaskTests:
         self.assertEqual(t._cancel_message, None)
 
         t.cancel('my message')
+        self.assertEqual(t._cancel_message, 'my message')
+
         with self.assertRaises(asyncio.CancelledError):
             self.loop.run_until_complete(t)
-        self.assertEqual(t._cancel_message, 'my message')
 
     def test_task_cancel_message_setter(self):
         async def coro():
@@ -123,10 +141,8 @@ class BaseTaskTests:
         t._cancel_message = 'my new message'
         self.assertEqual(t._cancel_message, 'my new message')
 
-        # Also check that the value is used for cancel().
         with self.assertRaises(asyncio.CancelledError):
             self.loop.run_until_complete(t)
-        self.assertEqual(t._cancel_message, 'my new message')
 
     def test_task_del_collect(self):
         class Evil:
@@ -548,8 +564,8 @@ class BaseTaskTests:
     def test_cancel_with_message_then_future_result(self):
         # Test Future.result() after calling cancel() with a message.
         cases = [
-            ((), ('',)),
-            ((None,), ('',)),
+            ((), ()),
+            ((None,), ()),
             (('my message',), ('my message',)),
             # Non-string values should roundtrip.
             ((5,), (5,)),
@@ -573,13 +589,17 @@ class BaseTaskTests:
                 with self.assertRaises(asyncio.CancelledError) as cm:
                     loop.run_until_complete(task)
                 exc = cm.exception
-                self.assertEqual(exc.args, expected_args)
+                self.assertEqual(exc.args, ())
+
+                actual = get_innermost_context(exc)
+                self.assertEqual(actual,
+                    (asyncio.CancelledError, expected_args, 2))
 
     def test_cancel_with_message_then_future_exception(self):
         # Test Future.exception() after calling cancel() with a message.
         cases = [
-            ((), ('',)),
-            ((None,), ('',)),
+            ((), ()),
+            ((None,), ()),
             (('my message',), ('my message',)),
             # Non-string values should roundtrip.
             ((5,), (5,)),
@@ -603,7 +623,11 @@ class BaseTaskTests:
                 with self.assertRaises(asyncio.CancelledError) as cm:
                     loop.run_until_complete(task)
                 exc = cm.exception
-                self.assertEqual(exc.args, expected_args)
+                self.assertEqual(exc.args, ())
+
+                actual = get_innermost_context(exc)
+                self.assertEqual(actual,
+                    (asyncio.CancelledError, expected_args, 2))
 
     def test_cancel_with_message_before_starting_task(self):
         loop = asyncio.new_event_loop()
@@ -623,7 +647,11 @@ class BaseTaskTests:
         with self.assertRaises(asyncio.CancelledError) as cm:
             loop.run_until_complete(task)
         exc = cm.exception
-        self.assertEqual(exc.args, ('my message',))
+        self.assertEqual(exc.args, ())
+
+        actual = get_innermost_context(exc)
+        self.assertEqual(actual,
+            (asyncio.CancelledError, ('my message',), 2))
 
     def test_cancel_yield(self):
         with self.assertWarns(DeprecationWarning):
@@ -805,6 +833,66 @@ class BaseTaskTests:
         self.assertTrue(nested_task.cancelled())
         self.assertTrue(fut.cancelled())
 
+    def assert_text_contains(self, text, substr):
+        if substr not in text:
+            raise RuntimeError(f'text {substr!r} not found in:\n>>>{text}<<<')
+
+    def test_cancel_traceback_for_future_result(self):
+        # When calling Future.result() on a cancelled task, check that the
+        # line of code that was interrupted is included in the traceback.
+        loop = asyncio.new_event_loop()
+        self.set_event_loop(loop)
+
+        async def nested():
+            # This will get cancelled immediately.
+            await asyncio.sleep(10)
+
+        async def coro():
+            task = self.new_task(loop, nested())
+            await asyncio.sleep(0)
+            task.cancel()
+            await task  # search target
+
+        task = self.new_task(loop, coro())
+        try:
+            loop.run_until_complete(task)
+        except asyncio.CancelledError:
+            tb = traceback.format_exc()
+            self.assert_text_contains(tb, "await asyncio.sleep(10)")
+            # The intermediate await should also be included.
+            self.assert_text_contains(tb, "await task  # search target")
+        else:
+            self.fail('CancelledError did not occur')
+
+    def test_cancel_traceback_for_future_exception(self):
+        # When calling Future.exception() on a cancelled task, check that the
+        # line of code that was interrupted is included in the traceback.
+        loop = asyncio.new_event_loop()
+        self.set_event_loop(loop)
+
+        async def nested():
+            # This will get cancelled immediately.
+            await asyncio.sleep(10)
+
+        async def coro():
+            task = self.new_task(loop, nested())
+            await asyncio.sleep(0)
+            task.cancel()
+            done, pending = await asyncio.wait([task])
+            task.exception()  # search target
+
+        task = self.new_task(loop, coro())
+        try:
+            loop.run_until_complete(task)
+        except asyncio.CancelledError:
+            tb = traceback.format_exc()
+            self.assert_text_contains(tb, "await asyncio.sleep(10)")
+            # The intermediate await should also be included.
+            self.assert_text_contains(tb,
+                "task.exception()  # search target")
+        else:
+            self.fail('CancelledError did not occur')
+
     def test_stop_while_run_in_complete(self):
 
         def gen():
@@ -2391,15 +2479,14 @@ class BaseTaskTests:
 
     def test_cancel_gather_2(self):
         cases = [
-            ((), ('',)),
-            ((None,), ('',)),
+            ((), ()),
+            ((None,), ()),
             (('my message',), ('my message',)),
             # Non-string values should roundtrip.
             ((5,), (5,)),
         ]
         for cancel_args, expected_args in cases:
             with self.subTest(cancel_args=cancel_args):
-
                 loop = asyncio.new_event_loop()
                 self.addCleanup(loop.close)
 
@@ -2417,15 +2504,20 @@ class BaseTaskTests:
                     qwe = self.new_task(loop, test())
                     await asyncio.sleep(0.2)
                     qwe.cancel(*cancel_args)
-                    try:
-                        await qwe
-                    except asyncio.CancelledError as exc:
-                        self.assertEqual(exc.args, expected_args)
-                    else:
-                        self.fail('gather did not propagate the cancellation '
-                                  'request')
-
-                loop.run_until_complete(main())
+                    await qwe
+
+                try:
+                    loop.run_until_complete(main())
+                except asyncio.CancelledError as exc:
+                    self.assertEqual(exc.args, ())
+                    exc_type, exc_args, depth = get_innermost_context(exc)
+                    self.assertEqual((exc_type, exc_args),
+                        (asyncio.CancelledError, expected_args))
+                    # The exact traceback seems to vary in CI.
+                    self.assertIn(depth, (2, 3))
+                else:
+                    self.fail('gather did not propagate the cancellation '
+                              'request')
 
     def test_exception_traceback(self):
         # See http://bugs.python.org/issue28843
diff --git a/Misc/NEWS.d/next/Library/2020-05-06-02-33-00.bpo-31033.aX12pw.rst b/Misc/NEWS.d/next/Library/2020-05-06-02-33-00.bpo-31033.aX12pw.rst
new file mode 100644
index 0000000..b1831e5
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-05-06-02-33-00.bpo-31033.aX12pw.rst
@@ -0,0 +1,2 @@
+When a :class:`asyncio.Task` is cancelled, the exception traceback
+now chains all the way back to where the task was first interrupted.
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index ff1b2b8..1b6a579 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -1,4 +1,5 @@
 #include "Python.h"
+#include "pycore_pyerrors.h"      // _PyErr_ClearExcState()
 #include <stddef.h>               // offsetof()
 
 
@@ -72,7 +73,8 @@ typedef enum {
     int prefix##_log_tb;                                                    \
     int prefix##_blocking;                                                  \
     PyObject *dict;                                                         \
-    PyObject *prefix##_weakreflist;
+    PyObject *prefix##_weakreflist;                                         \
+    _PyErr_StackItem prefix##_cancelled_exc_state;
 
 typedef struct {
     FutureObj_HEAD(fut)
@@ -482,6 +484,7 @@ future_init(FutureObj *fut, PyObject *loop)
     Py_CLEAR(fut->fut_exception);
     Py_CLEAR(fut->fut_source_tb);
     Py_CLEAR(fut->fut_cancel_msg);
+    _PyErr_ClearExcState(&fut->fut_cancelled_exc_state);
 
     fut->fut_state = STATE_PENDING;
     fut->fut_log_tb = 0;
@@ -601,9 +604,7 @@ create_cancelled_error(PyObject *msg)
 {
     PyObject *exc;
     if (msg == NULL || msg == Py_None) {
-        msg = PyUnicode_FromString("");
-        exc = PyObject_CallOneArg(asyncio_CancelledError, msg);
-        Py_DECREF(msg);
+        exc = PyObject_CallNoArgs(asyncio_CancelledError);
     } else {
         exc = PyObject_CallOneArg(asyncio_CancelledError, msg);
     }
@@ -623,6 +624,7 @@ future_get_result(FutureObj *fut, PyObject **result)
 {
     if (fut->fut_state == STATE_CANCELLED) {
         set_cancelled_error(fut->fut_cancel_msg);
+        _PyErr_ChainStackItem(&fut->fut_cancelled_exc_state);
         return -1;
     }
 
@@ -777,6 +779,7 @@ FutureObj_clear(FutureObj *fut)
     Py_CLEAR(fut->fut_exception);
     Py_CLEAR(fut->fut_source_tb);
     Py_CLEAR(fut->fut_cancel_msg);
+    _PyErr_ClearExcState(&fut->fut_cancelled_exc_state);
     Py_CLEAR(fut->dict);
     return 0;
 }
@@ -793,6 +796,12 @@ FutureObj_traverse(FutureObj *fut, visitproc visit, void *arg)
     Py_VISIT(fut->fut_source_tb);
     Py_VISIT(fut->fut_cancel_msg);
     Py_VISIT(fut->dict);
+
+    _PyErr_StackItem *exc_state = &fut->fut_cancelled_exc_state;
+    Py_VISIT(exc_state->exc_type);
+    Py_VISIT(exc_state->exc_value);
+    Py_VISIT(exc_state->exc_traceback);
+
     return 0;
 }
 
@@ -858,6 +867,7 @@ _asyncio_Future_exception_impl(FutureObj *self)
 
     if (self->fut_state == STATE_CANCELLED) {
         set_cancelled_error(self->fut_cancel_msg);
+        _PyErr_ChainStackItem(&self->fut_cancelled_exc_state);
         return NULL;
     }
 
@@ -1336,6 +1346,29 @@ FutureObj_get_state(FutureObj *fut, void *Py_UNUSED(ignored))
 }
 
 /*[clinic input]
+_asyncio.Future._make_cancelled_error
+
+Create the CancelledError to raise if the Future is cancelled.
+
+This should only be called once when handling a cancellation since
+it erases the context exception value.
+[clinic start generated code]*/
+
+static PyObject *
+_asyncio_Future__make_cancelled_error_impl(FutureObj *self)
+/*[clinic end generated code: output=a5df276f6c1213de input=ac6effe4ba795ecc]*/
+{
+    PyObject *exc = create_cancelled_error(self->fut_cancel_msg);
+    _PyErr_StackItem *exc_state = &self->fut_cancelled_exc_state;
+    /* Transfer ownership of exc_value from exc_state to exc since we are
+       done with it. */
+    PyException_SetContext(exc, exc_state->exc_value);
+    exc_state->exc_value = NULL;
+
+    return exc;
+}
+
+/*[clinic input]
 _asyncio.Future._repr_info
 [clinic start generated code]*/
 
@@ -1461,6 +1494,7 @@ static PyMethodDef FutureType_methods[] = {
     _ASYNCIO_FUTURE_CANCELLED_METHODDEF
     _ASYNCIO_FUTURE_DONE_METHODDEF
     _ASYNCIO_FUTURE_GET_LOOP_METHODDEF
+    _ASYNCIO_FUTURE__MAKE_CANCELLED_ERROR_METHODDEF
     _ASYNCIO_FUTURE__REPR_INFO_METHODDEF
     {"__class_getitem__", future_cls_getitem, METH_O|METH_CLASS, NULL},
     {NULL, NULL}        /* Sentinel */
@@ -2233,6 +2267,24 @@ _asyncio_Task_all_tasks_impl(PyTypeObject *type, PyObject *loop)
 }
 
 /*[clinic input]
+_asyncio.Task._make_cancelled_error
+
+Create the CancelledError to raise if the Task is cancelled.
+
+This should only be called once when handling a cancellation since
+it erases the context exception value.
+[clinic start generated code]*/
+
+static PyObject *
+_asyncio_Task__make_cancelled_error_impl(TaskObj *self)
+/*[clinic end generated code: output=55a819e8b4276fab input=52c0e32de8e2f840]*/
+{
+    FutureObj *fut = (FutureObj*)self;
+    return _asyncio_Future__make_cancelled_error_impl(fut);
+}
+
+
+/*[clinic input]
 _asyncio.Task._repr_info
 [clinic start generated code]*/
 
@@ -2539,6 +2591,7 @@ static PyMethodDef TaskType_methods[] = {
     _ASYNCIO_TASK_CANCEL_METHODDEF
     _ASYNCIO_TASK_GET_STACK_METHODDEF
     _ASYNCIO_TASK_PRINT_STACK_METHODDEF
+    _ASYNCIO_TASK__MAKE_CANCELLED_ERROR_METHODDEF
     _ASYNCIO_TASK__REPR_INFO_METHODDEF
     _ASYNCIO_TASK_GET_NAME_METHODDEF
     _ASYNCIO_TASK_SET_NAME_METHODDEF
@@ -2754,24 +2807,13 @@ task_step_impl(TaskObj *task, PyObject *exc)
             /* CancelledError */
             PyErr_Fetch(&et, &ev, &tb);
 
-            PyObject *cancel_msg;
-            if (ev != NULL && PyExceptionInstance_Check(ev)) {
-                PyObject *exc_args = ((PyBaseExceptionObject*)ev)->args;
-                Py_ssize_t size = PyTuple_GET_SIZE(exc_args);
-                if (size > 0) {
-                    cancel_msg = PyTuple_GET_ITEM(exc_args, 0);
-                } else {
-                    cancel_msg = NULL;
-                }
-            } else {
-                cancel_msg = ev;
-            }
-
-            Py_DECREF(et);
-            Py_XDECREF(tb);
-            Py_XDECREF(ev);
+            FutureObj *fut = (FutureObj*)task;
+            _PyErr_StackItem *exc_state = &fut->fut_cancelled_exc_state;
+            exc_state->exc_type = et;
+            exc_state->exc_value = ev;
+            exc_state->exc_traceback = tb;
 
-            return future_cancel((FutureObj*)task, cancel_msg);
+            return future_cancel(fut, NULL);
         }
 
         /* Some other exception; pop it and call Task.set_exception() */
diff --git a/Modules/clinic/_asynciomodule.c.h b/Modules/clinic/_asynciomodule.c.h
index 3f5023c..d3e59a4 100644
--- a/Modules/clinic/_asynciomodule.c.h
+++ b/Modules/clinic/_asynciomodule.c.h
@@ -271,6 +271,27 @@ _asyncio_Future_get_loop(FutureObj *self, PyObject *Py_UNUSED(ignored))
     return _asyncio_Future_get_loop_impl(self);
 }
 
+PyDoc_STRVAR(_asyncio_Future__make_cancelled_error__doc__,
+"_make_cancelled_error($self, /)\n"
+"--\n"
+"\n"
+"Create the CancelledError to raise if the Future is cancelled.\n"
+"\n"
+"This should only be called once when handling a cancellation since\n"
+"it erases the context exception value.");
+
+#define _ASYNCIO_FUTURE__MAKE_CANCELLED_ERROR_METHODDEF    \
+    {"_make_cancelled_error", (PyCFunction)_asyncio_Future__make_cancelled_error, METH_NOARGS, _asyncio_Future__make_cancelled_error__doc__},
+
+static PyObject *
+_asyncio_Future__make_cancelled_error_impl(FutureObj *self);
+
+static PyObject *
+_asyncio_Future__make_cancelled_error(FutureObj *self, PyObject *Py_UNUSED(ignored))
+{
+    return _asyncio_Future__make_cancelled_error_impl(self);
+}
+
 PyDoc_STRVAR(_asyncio_Future__repr_info__doc__,
 "_repr_info($self, /)\n"
 "--\n"
@@ -414,6 +435,27 @@ exit:
     return return_value;
 }
 
+PyDoc_STRVAR(_asyncio_Task__make_cancelled_error__doc__,
+"_make_cancelled_error($self, /)\n"
+"--\n"
+"\n"
+"Create the CancelledError to raise if the Task is cancelled.\n"
+"\n"
+"This should only be called once when handling a cancellation since\n"
+"it erases the context exception value.");
+
+#define _ASYNCIO_TASK__MAKE_CANCELLED_ERROR_METHODDEF    \
+    {"_make_cancelled_error", (PyCFunction)_asyncio_Task__make_cancelled_error, METH_NOARGS, _asyncio_Task__make_cancelled_error__doc__},
+
+static PyObject *
+_asyncio_Task__make_cancelled_error_impl(TaskObj *self);
+
+static PyObject *
+_asyncio_Task__make_cancelled_error(TaskObj *self, PyObject *Py_UNUSED(ignored))
+{
+    return _asyncio_Task__make_cancelled_error_impl(self);
+}
+
 PyDoc_STRVAR(_asyncio_Task__repr_info__doc__,
 "_repr_info($self, /)\n"
 "--\n"
@@ -870,4 +912,4 @@ _asyncio__leave_task(PyObject *module, PyObject *const *args, Py_ssize_t nargs,
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=6ed4cfda8fc516ad input=a9049054013a1b77]*/
+/*[clinic end generated code: output=0e5c1eb8b692977b input=a9049054013a1b77]*/
diff --git a/Objects/genobject.c b/Objects/genobject.c
index fb01e58..40179cd 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -3,6 +3,7 @@
 #include "Python.h"
 #include "pycore_ceval.h"         // _PyEval_EvalFrame()
 #include "pycore_object.h"
+#include "pycore_pyerrors.h"      // _PyErr_ClearExcState()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 #include "frameobject.h"
 #include "structmember.h"         // PyMemberDef
@@ -99,21 +100,6 @@ _PyGen_Finalize(PyObject *self)
     PyErr_Restore(error_type, error_value, error_traceback);
 }
 
-static inline void
-exc_state_clear(_PyErr_StackItem *exc_state)
-{
-    PyObject *t, *v, *tb;
-    t = exc_state->exc_type;
-    v = exc_state->exc_value;
-    tb = exc_state->exc_traceback;
-    exc_state->exc_type = NULL;
-    exc_state->exc_value = NULL;
-    exc_state->exc_traceback = NULL;
-    Py_XDECREF(t);
-    Py_XDECREF(v);
-    Py_XDECREF(tb);
-}
-
 static void
 gen_dealloc(PyGenObject *gen)
 {
@@ -146,7 +132,7 @@ gen_dealloc(PyGenObject *gen)
     Py_CLEAR(gen->gi_code);
     Py_CLEAR(gen->gi_name);
     Py_CLEAR(gen->gi_qualname);
-    exc_state_clear(&gen->gi_exc_state);
+    _PyErr_ClearExcState(&gen->gi_exc_state);
     PyObject_GC_Del(gen);
 }
 
@@ -286,7 +272,7 @@ gen_send_ex(PyGenObject *gen, PyObject *arg, int exc, int closing)
     if (!result || f->f_stacktop == NULL) {
         /* generator can't be rerun, so release the frame */
         /* first clean reference cycle through stored exception traceback */
-        exc_state_clear(&gen->gi_exc_state);
+        _PyErr_ClearExcState(&gen->gi_exc_state);
         gen->gi_frame->f_gen = NULL;
         gen->gi_frame = NULL;
         Py_DECREF(f);
diff --git a/Python/errors.c b/Python/errors.c
index f856a79..3b42c11 100644
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -512,6 +512,20 @@ _PyErr_ChainExceptions(PyObject *exc, PyObject *val, PyObject *tb)
     }
 }
 
+void
+_PyErr_ChainStackItem(_PyErr_StackItem *exc_state)
+{
+    if (exc_state->exc_type == NULL || exc_state->exc_type == Py_None) {
+        return;
+    }
+    Py_INCREF(exc_state->exc_type);
+    Py_XINCREF(exc_state->exc_value);
+    Py_XINCREF(exc_state->exc_traceback);
+    _PyErr_ChainExceptions(exc_state->exc_type,
+                           exc_state->exc_value,
+                           exc_state->exc_traceback);
+}
+
 static PyObject *
 _PyErr_FormatVFromCause(PyThreadState *tstate, PyObject *exception,
                         const char *format, va_list vargs)
diff --git a/setup.py b/setup.py
index 0f92a9c..847cf26 100644
--- a/setup.py
+++ b/setup.py
@@ -853,7 +853,8 @@ class PyBuildExt(build_ext):
         # _opcode module
         self.add(Extension('_opcode', ['_opcode.c']))
         # asyncio speedups
-        self.add(Extension("_asyncio", ["_asynciomodule.c"]))
+        self.add(Extension("_asyncio", ["_asynciomodule.c"],
+                           extra_compile_args=['-DPy_BUILD_CORE_MODULE']))
         # _abc speedups
         self.add(Extension("_abc", ["_abc.c"]))
         # _queue module