[Python-checkins] [3.6] bpo-34872: Fix self-cancellation in C implementation of asyncio.Task (GH-9679) (GH-9690)
Miss Islington (bot)
webhook-mailer at python.org
Wed Oct 3 11:28:52 EDT 2018
https://github.com/python/cpython/commit/166773df0ce6c852130f524029fa2e62b37b89cb
commit: 166773df0ce6c852130f524029fa2e62b37b89cb
branch: 3.6
author: Elvis Pranskevichus <elvis at magic.io>
committer: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
date: 2018-10-03T08:28:44-07:00
summary:
[3.6] bpo-34872: Fix self-cancellation in C implementation of asyncio.Task (GH-9679) (GH-9690)
The C implementation of asyncio.Task currently fails to perform the
cancellation cleanup correctly in the following scenario.
async def task1():
async def task2():
await task3 # task3 is never cancelled
asyncio.current_task().cancel()
await asyncio.create_task(task2())
The actuall error is a hardcoded call to `future_cancel()` instead of
calling the `cancel()` method of a future-like object.
Thanks to Vladimir Matveev for noticing the code discrepancy and to
Yury Selivanov for coming up with a pathological scenario.
(cherry picked from commit 548ce9dedd2e90945970671d441436a6a91608ab)
https://bugs.python.org/issue34872
files:
A Misc/NEWS.d/next/Library/2018-10-02-19-36-34.bpo-34872.yWZRhI.rst
M Lib/test/test_asyncio/test_tasks.py
M Modules/_asynciomodule.c
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index e8ec09efd4ad..084846bace3b 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -621,6 +621,42 @@ def task():
self.assertFalse(t._must_cancel) # White-box test.
self.assertFalse(t.cancel())
+ def test_cancel_awaited_task(self):
+ # This tests for a relatively rare condition when
+ # a task cancellation is requested for a task which is not
+ # currently blocked, such as a task cancelling itself.
+ # In this situation we must ensure that whatever next future
+ # or task the cancelled task blocks on is cancelled correctly
+ # as well. See also bpo-34872.
+ loop = asyncio.new_event_loop()
+ self.addCleanup(lambda: loop.close())
+
+ task = nested_task = None
+ fut = self.new_future(loop)
+
+ async def nested():
+ await fut
+
+ async def coro():
+ nonlocal nested_task
+ # Create a sub-task and wait for it to run.
+ nested_task = self.new_task(loop, nested())
+ await asyncio.sleep(0)
+
+ # Request the current task to be cancelled.
+ task.cancel()
+ # Block on the nested task, which should be immediately
+ # cancelled.
+ await nested_task
+
+ task = self.new_task(loop, coro())
+ with self.assertRaises(asyncio.CancelledError):
+ loop.run_until_complete(task)
+
+ self.assertTrue(task.cancelled())
+ self.assertTrue(nested_task.cancelled())
+ self.assertTrue(fut.cancelled())
+
def test_stop_while_run_in_complete(self):
def gen():
diff --git a/Misc/NEWS.d/next/Library/2018-10-02-19-36-34.bpo-34872.yWZRhI.rst b/Misc/NEWS.d/next/Library/2018-10-02-19-36-34.bpo-34872.yWZRhI.rst
new file mode 100644
index 000000000000..cd027102d012
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-10-02-19-36-34.bpo-34872.yWZRhI.rst
@@ -0,0 +1 @@
+Fix self-cancellation in C implementation of asyncio.Task
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index 6ad3d726f5ce..cbd6fe3c4455 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -2121,14 +2121,19 @@ task_step_impl(TaskObj *task, PyObject *exc)
if (task->task_must_cancel) {
PyObject *r;
- r = future_cancel(fut);
+ int is_true;
+ r = _PyObject_CallMethodId(fut, &PyId_cancel, NULL);
if (r == NULL) {
return NULL;
}
- if (r == Py_True) {
+ is_true = PyObject_IsTrue(r);
+ Py_DECREF(r);
+ if (is_true < 0) {
+ return NULL;
+ }
+ else if (is_true) {
task->task_must_cancel = 0;
}
- Py_DECREF(r);
}
Py_RETURN_NONE;
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