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Update README with long-polling usage example

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Daniel Alberto Cañas 2014-09-12 16:26:30 -06:00
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@ -108,6 +108,28 @@ That's cleaner than having to interop directly with the Java SDK, but it's all
pretty pedestrian stuff. You can do more interesting things with some
simple higher-order functions and other nifty Clojure facilities.
### Enabling SQS Long Polling
[Long polling](http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-long-polling.html) reduces the number of empty responses by allowing Amazon SQS service to wait until a message is available in the queue before sending a response. You can enable long polling on an individual receive request by supplying the optional kwarg `:wait-time-seconds`:
:wait-time-seconds - time in seconds (bewteen 0 and 20) for SQS to wait if there are no messages in the queue. A value of 0 indicates no long polling.
```clojure
; ensure our queue is empty to start
#> (get (sqs/queue-attrs client q) "ApproximateNumberOfMessages")
"0"
#> (let [no-polling (future (sqs/receive client q))
long-polling (future (sqs/receive client q :wait-time-seconds 20))]
(Thread/sleep 10000) ;; Sleep 10s before sending message
(sqs/send client q "my message body")
(println (count @no-polling))
(println (count @long-polling)))
0
1
nil
```
### Sending and receiving Clojure values
SQS' message bodies are strings, so you can stuff anything in them that you can