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-rw-r--r--Lib/asyncio/base_futures.py25
-rw-r--r--Lib/test/test_asyncio/test_futures2.py18
-rw-r--r--Misc/NEWS.d/next/Library/2020-10-29-11-17-35.bpo-42183.50ZcIi.rst4
3 files changed, 44 insertions, 3 deletions
diff --git a/Lib/asyncio/base_futures.py b/Lib/asyncio/base_futures.py
index 22f2980..2c01ac9 100644
--- a/Lib/asyncio/base_futures.py
+++ b/Lib/asyncio/base_futures.py
@@ -1,6 +1,7 @@
__all__ = ()
import reprlib
+from _thread import get_ident
from . import format_helpers
@@ -41,6 +42,16 @@ def _format_callbacks(cb):
return f'cb=[{cb}]'
+# bpo-42183: _repr_running is needed for repr protection
+# when a Future or Task result contains itself directly or indirectly.
+# The logic is borrowed from @reprlib.recursive_repr decorator.
+# Unfortunately, the direct decorator usage is impossible because of
+# AttributeError: '_asyncio.Task' object has no attribute '__module__' error.
+#
+# After fixing this thing we can return to the decorator based approach.
+_repr_running = set()
+
+
def _future_repr_info(future):
# (Future) -> str
"""helper function for Future.__repr__"""
@@ -49,9 +60,17 @@ def _future_repr_info(future):
if future._exception is not None:
info.append(f'exception={future._exception!r}')
else:
- # use reprlib to limit the length of the output, especially
- # for very long strings
- result = reprlib.repr(future._result)
+ key = id(future), get_ident()
+ if key in _repr_running:
+ result = '...'
+ else:
+ _repr_running.add(key)
+ try:
+ # use reprlib to limit the length of the output, especially
+ # for very long strings
+ result = reprlib.repr(future._result)
+ finally:
+ _repr_running.discard(key)
info.append(f'result={result}')
if future._callbacks:
info.append(_format_callbacks(future._callbacks))
diff --git a/Lib/test/test_asyncio/test_futures2.py b/Lib/test/test_asyncio/test_futures2.py
new file mode 100644
index 0000000..13dbc70
--- /dev/null
+++ b/Lib/test/test_asyncio/test_futures2.py
@@ -0,0 +1,18 @@
+# IsolatedAsyncioTestCase based tests
+import asyncio
+import unittest
+
+
+class FutureTests(unittest.IsolatedAsyncioTestCase):
+ async def test_recursive_repr_for_pending_tasks(self):
+ # The call crashes if the guard for recursive call
+ # in base_futures:_future_repr_info is absent
+ # See Also: https://bugs.python.org/issue42183
+
+ async def func():
+ return asyncio.all_tasks()
+
+ # The repr() call should not raise RecursiveError at first.
+ # The check for returned string is not very reliable but
+ # exact comparison for the whole string is even weaker.
+ self.assertIn('...', repr(await asyncio.wait_for(func(), timeout=10)))
diff --git a/Misc/NEWS.d/next/Library/2020-10-29-11-17-35.bpo-42183.50ZcIi.rst b/Misc/NEWS.d/next/Library/2020-10-29-11-17-35.bpo-42183.50ZcIi.rst
new file mode 100644
index 0000000..f6d7653
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-10-29-11-17-35.bpo-42183.50ZcIi.rst
@@ -0,0 +1,4 @@
+Fix a stack overflow error for asyncio Task or Future repr().
+
+The overflow occurs under some circumstances when a Task or Future
+recursively returns itself.