Issue #7105: weak dict iterators are fragile because of unpredictable GC runs

Backport the fix from pyton 3.x for this issue.

1 files changed, 49 insertions, 0 deletions

diff --git a/Lib/test/test_weakset.py b/Lib/test/test_weakset.py
index fb9e8d7..6b34a8d 100644
--- a/Lib/test/test_weakset.py
+++ b/Lib/test/test_weakset.py
@@ -11,6 +11,7 @@ import warnings
 import collections
 import gc
 import contextlib
+from UserString import UserString as ustr
 
 
 class Foo:
@@ -448,6 +449,54 @@ class TestWeakSet(unittest.TestCase):
             self.assertGreaterEqual(n2, 0)
             self.assertLessEqual(n2, n1)
 
+    def test_weak_destroy_while_iterating(self):
+        # Issue #7105: iterators shouldn't crash when a key is implicitly removed
+        # Create new items to be sure no-one else holds a reference
+        items = [ustr(c) for c in ('a', 'b', 'c')]
+        s = WeakSet(items)
+        it = iter(s)
+        next(it)             # Trigger internal iteration
+        # Destroy an item
+        del items[-1]
+        gc.collect()    # just in case
+        # We have removed either the first consumed items, or another one
+        self.assertIn(len(list(it)), [len(items), len(items) - 1])
+        del it
+        # The removal has been committed
+        self.assertEqual(len(s), len(items))
+
+    def test_weak_destroy_and_mutate_while_iterating(self):
+        # Issue #7105: iterators shouldn't crash when a key is implicitly removed
+        items = [ustr(c) for c in string.ascii_letters]
+        s = WeakSet(items)
+        @contextlib.contextmanager
+        def testcontext():
+            try:
+                it = iter(s)
+                next(it)
+                # Schedule an item for removal and recreate it
+                u = ustr(str(items.pop()))
+                gc.collect()      # just in case
+                yield u
+            finally:
+                it = None           # should commit all removals
+
+        with testcontext() as u:
+            self.assertFalse(u in s)
+        with testcontext() as u:
+            self.assertRaises(KeyError, s.remove, u)
+        self.assertFalse(u in s)
+        with testcontext() as u:
+            s.add(u)
+        self.assertTrue(u in s)
+        t = s.copy()
+        with testcontext() as u:
+            s.update(t)
+        self.assertEqual(len(s), len(t))
+        with testcontext() as u:
+            s.clear()
+        self.assertEqual(len(s), 0)
+
 
 def test_main(verbose=None):
     test_support.run_unittest(TestWeakSet)