pythongh-127085: fix memoryview->exports race condition.

Lib/test/test_free_threading/test_memoryview.py

@@ -0,0 +1,36 @@
+import multiprocessing.shared_memory
+from threading import Thread
+import unittest
+
+from test.support import threading_helper
+
+
+class TestBase(unittest.TestCase):
+    pass
+
+
+def do_race():
+    """Repeatly access the memoryview for racing."""
+    n = 100
+
+    obj = multiprocessing.shared_memory.ShareableList("Uq..SeDAmB+EBrkLl.SG.Z+Z.ZdsV..wT+zLxKwdN\b")
+    threads = []
+    for _ in range(n):
+        threads.append(Thread(target=obj.count, args=(1,)))
+
+    for t in threads:
+        t.start()
+
+    for t in threads:
+        t.join()
+
+    del obj
+
+
+@threading_helper.requires_working_threading()
+class TestMemoryView(TestBase):
+    def test_racing_getbuf_and_releasebuf(self):
+        do_race()
+
+if __name__ == "__main__":
+    unittest.main()

Objects/memoryobject.c

@@ -1589,7 +1589,9 @@ memory_getbuf(PyObject *_self, Py_buffer *view, int flags)
 
 
     view->obj = Py_NewRef(self);
+    Py_BEGIN_CRITICAL_SECTION(self);
     self->exports++;
+    Py_END_CRITICAL_SECTION();
 
     return 0;
 }
@@ -1598,7 +1600,9 @@ static void
 memory_releasebuf(PyObject *_self, Py_buffer *view)
 {
     PyMemoryViewObject *self = (PyMemoryViewObject *)_self;
+    Py_BEGIN_CRITICAL_SECTION(self);
     self->exports--;
+    Py_END_CRITICAL_SECTION();
     return;
     /* PyBuffer_Release() decrements view->obj after this function returns. */
 }