[3.6] bpo-30347: Stop crashes when concurrently iterate over itertools.groupby() iterators. (GH-1557) (#3770)

(cherry picked from commit c740e4fe8a9bc5815dc18c38d7f7600b128c3c51)

1 files changed, 31 insertions, 36 deletions

diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 21c0e82..3ff597b 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -72,10 +72,37 @@ groupby_traverse(groupbyobject *gbo, visitproc visit, void *arg)
     return 0;
 }
 
+Py_LOCAL_INLINE(int)
+groupby_step(groupbyobject *gbo)
+{
+    PyObject *newvalue, *newkey, *oldvalue;
+
+    newvalue = PyIter_Next(gbo->it);
+    if (newvalue == NULL)
+        return -1;
+
+    if (gbo->keyfunc == Py_None) {
+        newkey = newvalue;
+        Py_INCREF(newvalue);
+    } else {
+        newkey = PyObject_CallFunctionObjArgs(gbo->keyfunc, newvalue, NULL);
+        if (newkey == NULL) {
+            Py_DECREF(newvalue);
+            return -1;
+        }
+    }
+
+    oldvalue = gbo->currvalue;
+    gbo->currvalue = newvalue;
+    Py_XSETREF(gbo->currkey, newkey);
+    Py_XDECREF(oldvalue);
+    return 0;
+}
+
 static PyObject *
 groupby_next(groupbyobject *gbo)
 {
-    PyObject *newvalue, *newkey, *r, *grouper;
+    PyObject *r, *grouper;
 
     /* skip to next iteration group */
     for (;;) {
@@ -93,25 +120,9 @@ groupby_next(groupbyobject *gbo)
                 break;
         }
 
-        newvalue = PyIter_Next(gbo->it);
-        if (newvalue == NULL)
+        if (groupby_step(gbo) < 0)
             return NULL;
-
-        if (gbo->keyfunc == Py_None) {
-            newkey = newvalue;
-            Py_INCREF(newvalue);
-        } else {
-            newkey = PyObject_CallFunctionObjArgs(gbo->keyfunc, newvalue, NULL);
-            if (newkey == NULL) {
-                Py_DECREF(newvalue);
-                return NULL;
-            }
-        }
-
-        Py_XSETREF(gbo->currkey, newkey);
-        Py_XSETREF(gbo->currvalue, newvalue);
     }
-
     Py_INCREF(gbo->currkey);
     Py_XSETREF(gbo->tgtkey, gbo->currkey);
 
@@ -282,28 +293,12 @@ static PyObject *
 _grouper_next(_grouperobject *igo)
 {
     groupbyobject *gbo = (groupbyobject *)igo->parent;
-    PyObject *newvalue, *newkey, *r;
+    PyObject *r;
     int rcmp;
 
     if (gbo->currvalue == NULL) {
-        newvalue = PyIter_Next(gbo->it);
-        if (newvalue == NULL)
+        if (groupby_step(gbo) < 0)
             return NULL;
-
-        if (gbo->keyfunc == Py_None) {
-            newkey = newvalue;
-            Py_INCREF(newvalue);
-        } else {
-            newkey = PyObject_CallFunctionObjArgs(gbo->keyfunc, newvalue, NULL);
-            if (newkey == NULL) {
-                Py_DECREF(newvalue);
-                return NULL;
-            }
-        }
-
-        assert(gbo->currkey == NULL);
-        gbo->currkey = newkey;
-        gbo->currvalue = newvalue;
     }
 
     assert(gbo->currkey != NULL);