[beachy]

Long polling works brilliantly (where your API call blocks until there are some results or until timeout occurs - then you loop and call again).

Long polling gives you the best of both worlds - easy programming model with instant alerting rather than the delay of normal polling.

The only downside really is the need for a more or less permanently open connection per client. As long as the server does not use a naive "thread per connection" model this can scale up to many hundreds of thousands of clients or more.

[Animats]

The good thing about long polling is that if the connection breaks, the keep-alive will time out and you'll know you're not getting updates. Assuming there's some keep-alive feature.