bpo-42536: GC track recycled tuples (GH-23623)
Several built-in and standard library types now ensure that their internal result tuples are always tracked by the garbage collector:
- collections.OrderedDict.items
- dict.items
- enumerate
- functools.reduce
- itertools.combinations
- itertools.combinations_with_replacement
- itertools.permutations
- itertools.product
- itertools.zip_longest
- zip
Previously, they could have become untracked by a prior garbage collection.
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index df2997e..a99b5e2 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -12,6 +12,8 @@
import sys
import struct
import threading
+import gc
+
maxsize = support.MAX_Py_ssize_t
minsize = -maxsize-1
@@ -1573,6 +1575,51 @@ def test_StopIteration(self):
self.assertRaises(StopIteration, next, f(lambda x:x, []))
self.assertRaises(StopIteration, next, f(lambda x:x, StopNow()))
+ @support.cpython_only
+ def test_combinations_result_gc(self):
+ # bpo-42536: combinations's tuple-reuse speed trick breaks the GC's
+ # assumptions about what can be untracked. Make sure we re-track result
+ # tuples whenever we reuse them.
+ it = combinations([None, []], 1)
+ next(it)
+ gc.collect()
+ # That GC collection probably untracked the recycled internal result
+ # tuple, which has the value (None,). Make sure it's re-tracked when
+ # it's mutated and returned from __next__:
+ self.assertTrue(gc.is_tracked(next(it)))
+
+ @support.cpython_only
+ def test_combinations_with_replacement_result_gc(self):
+ # Ditto for combinations_with_replacement.
+ it = combinations_with_replacement([None, []], 1)
+ next(it)
+ gc.collect()
+ self.assertTrue(gc.is_tracked(next(it)))
+
+ @support.cpython_only
+ def test_permutations_result_gc(self):
+ # Ditto for permutations.
+ it = permutations([None, []], 1)
+ next(it)
+ gc.collect()
+ self.assertTrue(gc.is_tracked(next(it)))
+
+ @support.cpython_only
+ def test_product_result_gc(self):
+ # Ditto for product.
+ it = product([None, []])
+ next(it)
+ gc.collect()
+ self.assertTrue(gc.is_tracked(next(it)))
+
+ @support.cpython_only
+ def test_zip_longest_result_gc(self):
+ # Ditto for zip_longest.
+ it = zip_longest([[]])
+ gc.collect()
+ self.assertTrue(gc.is_tracked(next(it)))
+
+
class TestExamples(unittest.TestCase):
def test_accumulate(self):