Refactoring threadpool worker to make failures in test__issue6 and related easier to find and fix.

Only happens on Travis. Recently, the failure has started including 'Fatal Python error: PyImport_GetModuleDict missing'.

src/gevent/hub.py

@@ -486,10 +486,14 @@ class Hub(WaitOperationsGreenlet):
             that should generally result in exiting the loop and being
             thrown to the parent greenlet.
         """
+        if (type, value, tb) == (None, None, None):
+            type, value, tb = sys.exc_info()
+
         if isinstance(value, str):
             # Cython can raise errors where the value is a plain string
             # e.g., AttributeError, "_semaphore.Semaphore has no attr", <traceback>
             value = type(value)
+
         if not issubclass(type, self.NOT_ERROR):
             self.print_exception(context, type, value, tb)
         if context is None or issubclass(type, self.SYSTEM_ERROR):

src/gevent/testing/hub.py

@@ -29,6 +29,9 @@ class QuietHub(Hub):
     EXPECTED_TEST_ERROR = (ExpectedException,)
 
     def handle_error(self, context, type, value, tb):
+        if (type, value, tb) == (None, None, None):
+            import sys
+            type, value, tb = sys.exc_info()
         if issubclass(type, self.EXPECTED_TEST_ERROR):
             # Don't print these to cut down on the noise in the test logs
             return

src/gevent/tests/test__issue6.py

 from __future__ import print_function
+from __future__ import absolute_import
+from __future__ import division
+
 import sys
 
 if not sys.argv[1:]:
@@ -27,6 +30,7 @@ elif sys.argv[1:] == ['subprocess']: # pragma: no cover
         except NameError:
             line = input()
         print('%s chars.' % len(line))
+        sys.stdout.flush()
 
     gevent.spawn(printline).join()