Fix for waitall with nothing running

eventlet/greenpool.py

@@ -119,7 +119,8 @@ class GreenPool(object):
 
     def waitall(self):
         """Waits until all greenthreads in the pool are finished working."""
-        self.no_coros_running.wait()
+        if self.running():
+            self.no_coros_running.wait()
     
     def _spawn_done(self, coro):
         self.sem.release()

tests/greenpool_test.py

@@ -298,6 +298,11 @@ class GreenPool(tests.LimitedTestCase):
         result_list = list(p.starmap(passthru, [(x,) for x in xrange(10)]))
         self.assertEquals(result_list, range(10))
 
+    def test_waitall_on_nothing(self):
+        p = greenpool.GreenPool()
+        p.waitall()
+
+            
 class GreenPile(tests.LimitedTestCase):
     def test_pile(self):
         p = greenpool.GreenPile(4)