Stackless issue python#222: fix main-tasklet termination with serial …

…mismatch

Fix the termination of a main-tasklet when serial_last_jump !=
initial_stub.serial. This caused an assertion failure and a reference
leak.

(cherry picked from commit 0b8da63)

Stackless/changelog.txt

@@ -9,6 +9,10 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://github.com/stackless-dev/stackless/issues/221
+  Fix a bug that could cause an assertion failure and a reference leak during
+  the termination of a main-tasklet, if an application embeds Stackless Python.
+
 - https://github.com/stackless-dev/stackless/issues/221
   Change the width of C-stack serial numbers to 64bit. This prevents overflows
   in long running applications with an embedded Stackless Python.

Stackless/module/scheduling.c

@@ -1441,8 +1441,13 @@ slp_tasklet_end(PyObject *retval)
          * the original stub if necessary. (Meanwhile, task->cstate may be an old nesting state and not
          * the original stub, so we take the stub from the tstate)
          */
-        if (ts->st.serial_last_jump != ts->st.initial_stub->serial)
-            slp_transfer_return(ts->st.initial_stub);
+        if (ts->st.serial_last_jump != ts->st.initial_stub->serial) {
+            Py_DECREF(retval);
+            SLP_STORE_NEXT_FRAME(ts, NULL);
+            slp_transfer_return(ts->st.initial_stub); /* does not return */
+            assert(0);
+            return NULL;
+        }
     }
 
     /* remove current from runnables.  We now own its reference. */