bpo-37261: Document sys.unraisablehook corner cases (GH-14059)
Document reference cycle and resurrected objects issues in
sys.unraisablehook() and threading.excepthook() documentation.
Fix test.support.catch_unraisable_exception(): __exit__() no longer
ignores unraisable exceptions.
Fix test_io test_writer_close_error_on_close(): use a second
catch_unraisable_exception() to catch the BufferedWriter unraisable
exception.
diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 174e045..7c0efc7 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -3040,17 +3040,13 @@
"""
Context manager catching unraisable exception using sys.unraisablehook.
- If the *object* attribute of the unraisable hook is set and the object is
- being finalized, the object is resurrected because the context manager
- stores a strong reference to it (cm.unraisable.object).
-
Storing the exception value (cm.unraisable.exc_value) creates a reference
cycle. The reference cycle is broken explicitly when the context manager
exits.
- Exiting the context manager clears the stored unraisable exception. It can
- trigger a new unraisable exception (ex: the resurrected object is finalized
- again and raises the same exception): it is silently ignored in this case.
+ Storing the object (cm.unraisable.object) can resurrect it if it is set to
+ an object which is being finalized. Exiting the context manager clears the
+ stored object.
Usage:
@@ -3080,10 +3076,5 @@
return self
def __exit__(self, *exc_info):
- # Clear the unraisable exception to explicitly break a reference cycle.
- # It can call _hook() again: ignore the new unraisable exception in
- # this case.
- self.unraisable = None
-
sys.unraisablehook = self._old_hook
del self.unraisable
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 55686d7..fc474c9 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -2072,8 +2072,12 @@
writer.close = lambda: None
writer = None
+ # Ignore BufferedWriter (of the BufferedRWPair) unraisable exception
with support.catch_unraisable_exception():
- pair = None
+ # Ignore BufferedRWPair unraisable exception
+ with support.catch_unraisable_exception():
+ pair = None
+ support.gc_collect()
support.gc_collect()
def test_reader_writer_close_error_on_close(self):