Stackless issue python#218: Fix using Stackless as embedded Python interpreter

The fix for Stackless issue 186 (support for sub-interpreters) broke
some typical use cases.

(cherry picked from commit 5b29b24)

Author: Anselm Kruis

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/218
+  Fix using Stackless as embedded Python interpreter. The fix for Stackless
+  issue 186 (support for sub-interpreters) broke some typical use cases.
+
 - https://github.com/stackless-dev/stackless/issues/220
   Improve the error handling in case of failed stack transfers / hard tasklet
   switches. Call Py_FatalError, if a clean recovery is impossible.
@@ -17,7 +21,7 @@ What's New in Stackless 3.X.X?
   C-API documentation update: update the names of watchdog flags to match the
   implementation.
 
-- https://github.com/stackless-dev/stackless/issues/221
+- https://github.com/stackless-dev/stackless/issues/222
   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.
 

Stackless/core/stacklesseval.c

@@ -352,7 +352,7 @@ slp_eval_frame(PyFrameObject *f)
             retval = climb_stack_and_eval_frame(f);
 			initial_stub = ts->st.initial_stub;
 			/* cst might be NULL in OOM conditions */
-			if (initial_stub != NULL) {
+			if (ts->interp != _PyRuntime.interpreters.main && initial_stub != NULL) {
                 PyCStackObject *cst;
                 register int found = 0;
                 assert(initial_stub->startaddr == ts->st.cstack_base);

Stackless/unittests/test_slp_embed.py

@@ -24,7 +24,6 @@ def setUp(self):
 from test.support import verbose
 
 
-@unittest.skip("Stackless issue 218")
 class EmbeddingTests(EmbeddingTestsMixin, unittest.TestCase):
     def test_schedule(self):
         env = dict(os.environ)