[Fix #10] Throttle client polling to avoid GET floods

After an HTTP request that returns no results, block on the incoming
queue for up to 100ms before retrying. This limits idle polling to
~10 requests/sec while still returning results immediately when
they're available.

Author: bbatsov

src/drawbridge/client.clj

@@ -47,7 +47,10 @@
          (or (.poll incoming 0 TimeUnit/MILLISECONDS)
              (when (pos? timeout)
                (http)
-               (recur (- timeout (- (System/currentTimeMillis) t)))))))
+               (or (.poll incoming (min timeout 100) TimeUnit/MILLISECONDS)
+                   (let [remaining (- timeout (- (System/currentTimeMillis) t))]
+                     (when (pos? remaining)
+                       (recur remaining))))))))
      http
      (fn close []))))