Backport r72961 fixing issue #6105: json.dumps not following OrderedDict iteration order.
diff --git a/Modules/_json.c b/Modules/_json.c
index d81721a..de7e171 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -2071,8 +2071,9 @@
     static PyObject *empty_dict = NULL;
     PyObject *kstr = NULL;
     PyObject *ident = NULL;
-    PyObject *key, *value;
-    Py_ssize_t pos;
+    PyObject *key = NULL;
+    PyObject *value = NULL;
+    PyObject *it = NULL;
     int skipkeys;
     Py_ssize_t idx;
 
@@ -2083,7 +2084,7 @@
         if (open_dict == NULL || close_dict == NULL || empty_dict == NULL)
             return -1;
     }
-    if (PyDict_Size(dct) == 0)
+    if (Py_SIZE(dct) == 0)
         return PyList_Append(rval, empty_dict);
 
     if (s->markers != Py_None) {
@@ -2117,10 +2118,12 @@
 
     /* TODO: C speedup not implemented for sort_keys */
 
-    pos = 0;
+    it = PyObject_GetIter(dct);
+    if (it == NULL)
+        goto bail;
     skipkeys = PyObject_IsTrue(s->skipkeys);
     idx = 0;
-    while (PyDict_Next(dct, &pos, &key, &value)) {
+    while ((key = PyIter_Next(it)) != NULL) {
         PyObject *encoded;
 
         if (PyString_Check(key) || PyUnicode_Check(key)) {
@@ -2143,6 +2146,7 @@
                 goto bail;
         }
         else if (skipkeys) {
+            Py_DECREF(key);
             continue;
         }
         else {
@@ -2156,6 +2160,10 @@
                 goto bail;
         }
 
+        value = PyObject_GetItem(dct, key);
+        if (value == NULL)
+            goto bail;
+
         encoded = encoder_encode_string(s, kstr);
         Py_CLEAR(kstr);
         if (encoded == NULL)
@@ -2170,7 +2178,13 @@
         if (encoder_listencode_obj(s, rval, value, indent_level))
             goto bail;
         idx += 1;
+        Py_CLEAR(value);
+        Py_DECREF(key);
     }
+    if (PyErr_Occurred())
+        goto bail;
+    Py_CLEAR(it);
+
     if (ident != NULL) {
         if (PyDict_DelItem(s->markers, ident))
             goto bail;
@@ -2189,6 +2203,9 @@
     return 0;
 
 bail:
+    Py_XDECREF(it);
+    Py_XDECREF(key);
+    Py_XDECREF(value);
     Py_XDECREF(kstr);
     Py_XDECREF(ident);
     return -1;