[Python-checkins] GH-89988: Fix memory leak in pickle.Pickler dispatch_table lookup (GH-94298)

[serhiy-storchaka]

https://github.com/python/cpython/commit/01ef1f95dab9c9930ce1a23634a3e5a8331bf3c7
commit: 01ef1f95dab9c9930ce1a23634a3e5a8331bf3c7
branch: main
author: Kumar Aditya <59607654+kumaraditya303 at users.noreply.github.com>
committer: serhiy-storchaka <storchaka at gmail.com>
date: 2022-06-28T10:01:43+03:00
summary:

GH-89988: Fix memory leak in pickle.Pickler dispatch_table lookup (GH-94298)

files:
A Misc/NEWS.d/next/Library/2022-06-26-10-59-15.gh-issue-89988.K8rnmt.rst
M Lib/test/test_pickle.py
M Modules/_pickle.c

diff --git a/Lib/test/test_pickle.py b/Lib/test/test_pickle.py
index 057af21e71fe4..44fdca7a6b168 100644
--- a/Lib/test/test_pickle.py
+++ b/Lib/test/test_pickle.py
@@ -154,6 +154,29 @@ def persistent_id(obj):
                 return obj
         check(PersPickler)
 
+    @support.cpython_only
+    def test_custom_pickler_dispatch_table_memleak(self):
+        # See https://github.com/python/cpython/issues/89988
+
+        class Pickler(self.pickler):
+            def __init__(self, *args, **kwargs):
+                self.dispatch_table = table
+                super().__init__(*args, **kwargs)
+
+        class DispatchTable:
+            pass
+
+        table = DispatchTable()
+        pickler = Pickler(io.BytesIO())
+        self.assertIs(pickler.dispatch_table, table)
+        table_ref = weakref.ref(table)
+        self.assertIsNotNone(table_ref())
+        del pickler
+        del table
+        support.gc_collect()
+        self.assertIsNone(table_ref())
+
+
     @support.cpython_only
     def test_unpickler_reference_cycle(self):
         def check(Unpickler):
diff --git a/Misc/NEWS.d/next/Library/2022-06-26-10-59-15.gh-issue-89988.K8rnmt.rst b/Misc/NEWS.d/next/Library/2022-06-26-10-59-15.gh-issue-89988.K8rnmt.rst
new file mode 100644
index 0000000000000..811a8d6031e0b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-06-26-10-59-15.gh-issue-89988.K8rnmt.rst
@@ -0,0 +1 @@
+Fix memory leak in :class:`pickle.Pickler` when looking up :attr:`dispatch_table`. Patch by Kumar Aditya.
diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index 1c5de30b07d62..52704b0c59ade 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -4761,7 +4761,9 @@ _pickle_Pickler___init___impl(PicklerObject *self, PyObject *file,
     {
         return -1;
     }
-
+    if (self->dispatch_table != NULL) {
+        return 0;
+    }
     if (_PyObject_LookupAttr((PyObject *)self, &_Py_ID(dispatch_table),
                              &self->dispatch_table) < 0) {
         return -1;