bpo-42183: Fix a stack overflow error for asyncio Task or Future repr() (GH-23020)
The overflow occurs under some circumstances when a task or future
recursively returns itself.
Co-authored-by: Kyle Stanley <aeros167@gmail.com>
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_cb(callback):
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))