Issue #14159: Fix the len() of weak containers (WeakSet, WeakKeyDictionary, WeakValueDictionary) to return a better approximation when some objects are dead or dying.
Moreover, the implementation is now O(1) rather than O(n).
Thanks to Yury Selivanov for reporting.
diff --git a/Lib/test/test_weakset.py b/Lib/test/test_weakset.py
index 3cddf40..35db7a6 100644
--- a/Lib/test/test_weakset.py
+++ b/Lib/test/test_weakset.py
@@ -17,6 +17,10 @@
class Foo:
pass
+class RefCycle:
+ def __init__(self):
+ self.cycle = self
+
class TestWeakSet(unittest.TestCase):
@@ -359,6 +363,49 @@
s.clear()
self.assertEqual(len(s), 0)
+ def test_len_cycles(self):
+ N = 20
+ items = [RefCycle() for i in range(N)]
+ s = WeakSet(items)
+ del items
+ it = iter(s)
+ try:
+ next(it)
+ except StopIteration:
+ pass
+ gc.collect()
+ n1 = len(s)
+ del it
+ gc.collect()
+ n2 = len(s)
+ # one item may be kept alive inside the iterator
+ self.assertIn(n1, (0, 1))
+ self.assertEqual(n2, 0)
+
+ def test_len_race(self):
+ # Extended sanity checks for len() in the face of cyclic collection
+ self.addCleanup(gc.set_threshold, *gc.get_threshold())
+ for th in range(1, 100):
+ N = 20
+ gc.collect(0)
+ gc.set_threshold(th, th, th)
+ items = [RefCycle() for i in range(N)]
+ s = WeakSet(items)
+ del items
+ # All items will be collected at next garbage collection pass
+ it = iter(s)
+ try:
+ next(it)
+ except StopIteration:
+ pass
+ n1 = len(s)
+ del it
+ n2 = len(s)
+ self.assertGreaterEqual(n1, 0)
+ self.assertLessEqual(n1, N)
+ self.assertGreaterEqual(n2, 0)
+ self.assertLessEqual(n2, n1)
+
def test_main(verbose=None):
support.run_unittest(TestWeakSet)