Catch the ValueError that sys._getframe() can raise when there are no Python frames.

This can happen in the embedded case, when the CPython C api is used to directly call Greenlet.spawn, which itself is now implemented in C.

Fixes #1212.

CHANGES.rst

@@ -9,6 +9,8 @@
 
 - Nothing changed yet.
 
+- Fix embedded uses of :func:`gevent.Greenlet.spawn`, especially under
+  uwsgi. Reported in :issue:`1212` by Kunal Gangakhedkar.
 
 1.3.0 (2018-05-11)
 ==================

src/gevent/greenlet.py

@@ -130,7 +130,18 @@ def _Frame_from_list(frames):
     return previous
 
 def _extract_stack(limit):
-    frame = sys_getframe()
+    try:
+        frame = sys_getframe()
+    except ValueError:
+        # In certain embedded cases that directly use the Python C api
+        # to call Greenlet.spawn (e.g., uwsgi) this can raise
+        # `ValueError: call stack is not deep enough`. This is because
+        # the Cython stack frames for Greenlet.spawn ->
+        # Greenlet.__init__ -> _extract_stack are all on the C level,
+        # not the Python level.
+        # See https://github.com/gevent/gevent/issues/1212
+        frame = None
+
     frames = []
 
     while limit and frame is not None:

src/greentest/test__greenlet.py

@@ -18,11 +18,12 @@
 # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
-
+import re
+import unittest
 
 import greentest
 import gevent
-import re
+
 from gevent import sleep, with_timeout, getcurrent
 from gevent import greenlet
 from gevent.event import AsyncResult
@@ -699,6 +700,22 @@ class TestBasic(greentest.TestCase):
             gevent.sleep(0.01)
 
 
+    def test_getframe_value_error(self):
+        def get():
+            raise ValueError("call stack is not deep enough")
+        try:
+            ogf = greenlet.sys_getframe
+        except AttributeError:
+            # Must be running cython compiled
+            raise unittest.SkipTest("Cannot mock when Cython compiled")
+        greenlet.sys_getframe = get
+        try:
+            child = greenlet.Greenlet()
+            self.assertIsNone(child.spawning_stack)
+        finally:
+            greenlet.sys_getframe = ogf
+
+
 class TestStart(greentest.TestCase):
 
     def test(self):