Quiet lookup errors from the threadpool by default. Ref #617 that was also...

Quiet lookup errors from the threadpool by default. Ref #617 that was also mentioned in a private email.

gevent/hub.py

@@ -398,6 +398,7 @@ class Hub(greenlet):
     #: Instances of these classes are not considered to be errors and
     #: do not get logged/printed when raised by the event loop.
     NOT_ERROR = (GreenletExit, SystemExit)
+
     loop_class = config('gevent.core.loop', 'GEVENT_LOOP')
     resolver_class = ['gevent.resolver_thread.Resolver',
                       'gevent.resolver_ares.Resolver',

gevent/resolver_thread.py

@@ -40,6 +40,10 @@ class Resolver(object):
         if hub is None:
             hub = get_hub()
         self.pool = hub.threadpool
+        if _socket.gaierror not in hub.NOT_ERROR:
+            # Do not cause lookup failures to get printed by the default
+            # error handler. This can be very noisy.
+            hub.NOT_ERROR += (_socket.gaierror, _socket.herror)
 
     def __repr__(self):
         return '<gevent.resolver_thread.Resolver at 0x%x pool=%r>' % (id(self), self.pool)