Fix memory leak caused by identity when default value is inplace (#1284)

Co-authored-by: J. Nick Koston <[email protected]>
Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 4 people

CHANGES/1284.bugfix.rst

@@ -0,0 +1,2 @@
+Fixed slow memory leak caused by identity by adding ``Py_DECREF`` to identity value before leaving ``md_pop_one`` on success
+-- by :user:`Vizonex`.

multidict/_multilib/hashtable.h

@@ -1019,7 +1019,7 @@ md_pop_one(MultiDictObject *md, PyObject *key, PyObject **ret)
             goto fail;
         }
     }
-
+    Py_DECREF(identity);
     ASSERT_CONSISTENT(md, false);
     return 0;
 fail:

tests/isolated/multidict_pop.py

@@ -63,6 +63,16 @@ def _test_popone() -> None:
         check_for_leak()
 
 
+# SEE: https://github.com/aio-libs/multidict/issues/1273
+def _test_pop_with_default() -> None:
+    # XXX: mypy wants an annotation so the only
+    # thing we can do here is pass the headers along.
+    result = MultiDict(headers)
+    for i in range(1_000_000):
+        result.pop(f"missing_key_{i}", None)
+    check_for_leak()
+
+
 def _test_del() -> None:
     for _ in range(10):
         for _ in range(100):
@@ -76,6 +86,7 @@ def _run_isolated_case() -> None:
     _test_pop()
     _test_popall()
     _test_popone()
+    _test_pop_with_default()
     _test_del()