Spoiler alert: I'm really really new to this language so don't expect
quality code
In an attempt to see how futures work I'm trying to make code that does the
following:
1. Take a list of sites
2. Loop through the sites and retrieve the HEAD content via a future for
each individual site
3. In the main loop once the futures have been created print the HEAD
content as each future completes
Now I have this code which I'm getting stuck at:
(ns cjr-http-test.core
(:require [clj-http.client :as client]))
(defn get-head-response-for-sites
[sites]
(map (fn [site] (future (client/head site))) sites))
(doseq [head-data (get-head-response-for-sites '("http://www.google.com";
"http://www.yahoo.com"; "http://www.bing.com";))]
(println (deref head-data)))
(shutdown-agents)
(Please note I know that the list of sites I'd normally expect to be
something from a DB/text file. I'm just trying to get it working without
adding extra things to think about)
So get-head-response-for-sites is where I'm trying to do #2. It gets me a
list of futures that I can use. Where I'm having trouble is that the
current println line, which is where I'm trying to deal with #3, blocks due
to deref-ing so it's basically not really all that different than if I did
it non threading.
What I (think) I need is something that keeps looping through all the
futures, checking their status, and println’ing the result when something
has come back. This will be repeated until all the futures are done. The
reason I want this is that for example if the first site takes 3 minutes to
respond I want the other two sites to print their HEAD content as soon as
it’s retrieved. Here's what I'm trying to figure out in order of importance:
1. How do I get a constant loop through the futures, println'ing the
HEAD content as they finish, until all futures are finished?
2. Is there a better way to structure this?
3. Is there something in Clojure/contrib that's better suited for this?
4. Is there a 3rd party library better suited for this?
Thanks for any and all response. Once again I apologize for the not so pro
code but some code is better than nothing I hope.
- Chris White ( @cwgem )
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