bpo-30508: Don't log exceptions if Task/Future "cancel()" method called (#2050)

4 files changed, 29 insertions, 0 deletions

diff --git a/Lib/asyncio/futures.py b/Lib/asyncio/futures.py
index 39721ea..215f72d 100644
--- a/Lib/asyncio/futures.py
+++ b/Lib/asyncio/futures.py
@@ -107,6 +107,7 @@ class Future:
         change the future's state to cancelled, schedule the callbacks and
         return True.
         """
+        self._log_traceback = False
         if self._state != _PENDING:
             return False
         self._state = _CANCELLED
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index e453300..575d205 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -144,6 +144,7 @@ class Task(futures.Future):
         terminates with a CancelledError exception (even if cancel()
         was not called).
         """
+        self._log_traceback = False
         if self.done():
             return False
         if self._fut_waiter is not None:
diff --git a/Lib/test/test_asyncio/test_futures.py b/Lib/test/test_asyncio/test_futures.py
index 99336f8..5d4b2d2 100644
--- a/Lib/test/test_asyncio/test_futures.py
+++ b/Lib/test/test_asyncio/test_futures.py
@@ -319,6 +319,14 @@ class BaseFutureTests:
         self.assertFalse(m_log.error.called)
 
     @mock.patch('asyncio.base_events.logger')
+    def test_tb_logger_not_called_after_cancel(self, m_log):
+        fut = self._new_future(loop=self.loop)
+        fut.set_exception(Exception())
+        fut.cancel()
+        del fut
+        self.assertFalse(m_log.error.called)
+
+    @mock.patch('asyncio.base_events.logger')
     def test_tb_logger_result_unretrieved(self, m_log):
         fut = self._new_future(loop=self.loop)
         fut.set_result(42)
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index 988b288..686387f 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -1864,6 +1864,25 @@ class BaseTaskTests:
         })
         mock_handler.reset_mock()
 
+    @mock.patch('asyncio.base_events.logger')
+    def test_tb_logger_not_called_after_cancel(self, m_log):
+        loop = asyncio.new_event_loop()
+        self.set_event_loop(loop)
+
+        @asyncio.coroutine
+        def coro():
+            raise TypeError
+
+        @asyncio.coroutine
+        def runner():
+            task = self.new_task(loop, coro())
+            yield from asyncio.sleep(0.05, loop=loop)
+            task.cancel()
+            task = None
+
+        loop.run_until_complete(runner())
+        self.assertFalse(m_log.error.called)
+
     @mock.patch('asyncio.coroutines.logger')
     def test_coroutine_never_yielded(self, m_log):
         with set_coroutine_debug(True):