ensure that new hub greenlet is parent of old, dead hub greenlet.

also, ensure this happens when eventlet.greenthread.kill() is used.

eventlet/greenthread.py

@@ -258,5 +258,6 @@ def kill(g, *throw_args):
     current = getcurrent()
     if current is not hub.greenlet:
         # arrange to wake the caller back up immediately
+        hub.ensure_greenlet()
         hub.schedule_call_global(0, current.switch)
     g.throw(*throw_args)

eventlet/hubs/hub.py

@@ -157,6 +157,17 @@ class BaseHub(object):
             except Exception, e:
                 self.squelch_generic_exception(sys.exc_info())
 
+    def ensure_greenlet(self):
+        if self.greenlet.dead:
+            # create new greenlet sharing same parent as original
+            new = greenlet.greenlet(self.run, self.greenlet.parent)
+            # need to assign as parent of old greenlet
+            # for those greenlets that are currently
+            # children of the dead hub and may subsequently
+            # exit without further switching to hub.
+            self.greenlet.parent = new
+            self.greenlet = new
+
     def switch(self):
         cur = greenlet.getcurrent()
         assert cur is not self.greenlet, 'Cannot switch to MAINLOOP from MAINLOOP'
@@ -166,8 +177,7 @@ class BaseHub(object):
                 switch_out()
             except:
                 self.squelch_generic_exception(sys.exc_info())
-        if self.greenlet.dead:
-            self.greenlet = greenlet.greenlet(self.run)
+        self.ensure_greenlet()
         try:
             if self.greenlet.parent is not cur:
                 cur.parent = self.greenlet