Issue #1868: Eliminate subtle timing issues in thread-local objects by

getting rid of the cached copy of thread-local attribute dictionary.

1 files changed, 65 insertions, 48 deletions

diff --git a/Objects/object.c b/Objects/object.c
index ef23ac1..3bde659 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -954,7 +954,7 @@ _PyObject_NextNotImplemented(PyObject *self)
 /* Generic GetAttr functions - put these in your tp_[gs]etattro slot */
 
 PyObject *
-PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
+_PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name, PyObject *dict)
 {
     PyTypeObject *tp = Py_TYPE(obj);
     PyObject *descr = NULL;
@@ -990,36 +990,37 @@ PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
         }
     }
 
-    /* Inline _PyObject_GetDictPtr */
-    dictoffset = tp->tp_dictoffset;
-    if (dictoffset != 0) {
-        PyObject *dict;
-        if (dictoffset < 0) {
-            Py_ssize_t tsize;
-            size_t size;
-
-            tsize = ((PyVarObject *)obj)->ob_size;
-            if (tsize < 0)
-                tsize = -tsize;
-            size = _PyObject_VAR_SIZE(tp, tsize);
-
-            dictoffset += (long)size;
-            assert(dictoffset > 0);
-            assert(dictoffset % SIZEOF_VOID_P == 0);
-        }
-        dictptr = (PyObject **) ((char *)obj + dictoffset);
-        dict = *dictptr;
-        if (dict != NULL) {
-            Py_INCREF(dict);
-            res = PyDict_GetItem(dict, name);
-            if (res != NULL) {
-                Py_INCREF(res);
-                Py_XDECREF(descr);
-                Py_DECREF(dict);
-                goto done;
+    if (dict == NULL) {
+        /* Inline _PyObject_GetDictPtr */
+        dictoffset = tp->tp_dictoffset;
+        if (dictoffset != 0) {
+            if (dictoffset < 0) {
+                Py_ssize_t tsize;
+                size_t size;
+
+                tsize = ((PyVarObject *)obj)->ob_size;
+                if (tsize < 0)
+                    tsize = -tsize;
+                size = _PyObject_VAR_SIZE(tp, tsize);
+
+                dictoffset += (long)size;
+                assert(dictoffset > 0);
+                assert(dictoffset % SIZEOF_VOID_P == 0);
             }
+            dictptr = (PyObject **) ((char *)obj + dictoffset);
+            dict = *dictptr;
+        }
+    }
+    if (dict != NULL) {
+        Py_INCREF(dict);
+        res = PyDict_GetItem(dict, name);
+        if (res != NULL) {
+            Py_INCREF(res);
+            Py_XDECREF(descr);
             Py_DECREF(dict);
+            goto done;
         }
+        Py_DECREF(dict);
     }
 
     if (f != NULL) {
@@ -1042,8 +1043,15 @@ PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
     return res;
 }
 
+PyObject *
+PyObject_GenericGetAttr(PyObject *obj, PyObject *name)
+{
+    return _PyObject_GenericGetAttrWithDict(obj, name, NULL);
+}
+
 int
-PyObject_GenericSetAttr(PyObject *obj, PyObject *name, PyObject *value)
+_PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
+                                 PyObject *value, PyObject *dict)
 {
     PyTypeObject *tp = Py_TYPE(obj);
     PyObject *descr;
@@ -1075,27 +1083,29 @@ PyObject_GenericSetAttr(PyObject *obj, PyObject *name, PyObject *value)
         }
     }
 
-    dictptr = _PyObject_GetDictPtr(obj);
-    if (dictptr != NULL) {
-        PyObject *dict = *dictptr;
-        if (dict == NULL && value != NULL) {
-            dict = PyDict_New();
-            if (dict == NULL)
-                goto done;
-            *dictptr = dict;
-        }
-        if (dict != NULL) {
-            Py_INCREF(dict);
-            if (value == NULL)
-                res = PyDict_DelItem(dict, name);
-            else
-                res = PyDict_SetItem(dict, name, value);
-            if (res < 0 && PyErr_ExceptionMatches(PyExc_KeyError))
-                PyErr_SetObject(PyExc_AttributeError, name);
-            Py_DECREF(dict);
-            goto done;
+    if (dict == NULL) {
+        dictptr = _PyObject_GetDictPtr(obj);
+        if (dictptr != NULL) {
+            dict = *dictptr;
+            if (dict == NULL && value != NULL) {
+                dict = PyDict_New();
+                if (dict == NULL)
+                    goto done;
+                *dictptr = dict;
+            }
         }
     }
+    if (dict != NULL) {
+        Py_INCREF(dict);
+        if (value == NULL)
+            res = PyDict_DelItem(dict, name);
+        else
+            res = PyDict_SetItem(dict, name, value);
+        if (res < 0 && PyErr_ExceptionMatches(PyExc_KeyError))
+            PyErr_SetObject(PyExc_AttributeError, name);
+        Py_DECREF(dict);
+        goto done;
+    }
 
     if (f != NULL) {
         res = f(descr, obj, value);
@@ -1117,6 +1127,13 @@ PyObject_GenericSetAttr(PyObject *obj, PyObject *name, PyObject *value)
     return res;
 }
 
+int
+PyObject_GenericSetAttr(PyObject *obj, PyObject *name, PyObject *value)
+{
+    return _PyObject_GenericSetAttrWithDict(obj, name, value, NULL);
+}
+
+
 /* Test a value used as condition, e.g., in a for or if statement.
    Return -1 if an error occurred */