Raise an exception if no sockets to poll

[loerum]

Trying to receive messages from a not registered service will create an infinite loop, the following code will print None forever:

from posttroll.subscriber import Subscribe
with Subscribe("invalid_service", "counter",) as sub:
for msg in sub.recv():
    print(msg)

It's fixed by raising an exception in Subscriber.recv if no socket to poll.

I'm some what surprised that we first see this "feature" now ... so please check if I have missed something.

[coveralls]

Coverage decreased (-0.09%) to 79.62% when pulling d34f427 on fix-infinite-loop into 516725e on master.

[loerum]

By the way, the above infinite loop, would not have happen if an addr_listener was specified:

from posttroll.subscriber import Subscribe
with Subscribe("invalid_service", "counter", addr_listener=True) as sub:
for msg in sub.recv():
    print(msg)

In this case, there is always something to poll. Maybe if a name-server is been used, addr_listener should have the default value True ?

[mraspaud]

I'm not in the office, please remind me to look at this next week

[mraspaud]

Thanks for this, could you add a small unit test for this @loerum ?