On Mon, Oct 22, 2012 at 2:30 PM, larry google groups
<[email protected]> wrote:
>
>
> And the core.clj looks like this:
>
> (ns who-is-logged-in.core
> (:gen-class)
> (:import (java.util Date))
> (:require clojure.string clojure.java.io who-is-logged-in.memory_display
> [clojure.data.json :as json])
> (:use [net.cgrand.moustache :only [app delegate]]
> [ring.util.response]
> [ring.middleware.params]
> [ring.adapter.jetty :only [run-jetty]]))
>
> (def registry (atom {}))
>
> (defn add-to-logged-in-registry [this-users-params]
> "We assume some user is looking at a site such as wpquestions.com and the
> Javascript on that site is sending an Ajax request to this app, every 10
> seconds, with a map of information about the user, which we need to store in
> the registry."
> (let [right-now (. (Date.) getTime)
Please do (System/currentTimeMillis) instead of allocating new Date
objects over and over.
> new-user-entry (conj this-users-params { "updated" right-now })]
> (if-not (nil? (get new-user-entry "username"))
> (swap! registry assoc (get new-user-entry "username")
> new-user-entry))))
>
> (defn is-current? [this-users-map]
> "If we have not received an Ajax request from a user during the last 15
> seconds then we can assume they have left the site. We need to remove them
> from registry."
> (let [most-recent-ping (get this-users-map "updated")
> allowed-cutoff (- (. (Date.) getTime) 15000)]
> (if (> most-recent-ping allowed-cutoff)
> true
> false)))
>
> (defn remove-old-registrants []
> "The registry should only show people who have pinged this app during the
> last 15 seconds. We rebuild the registry with only those users whose maps
> return true from is-current?"
> (def updated-registry {})
This def is too ugly to live, and possibly a memory leak. Is it also
always empty?
> (swap! registry (fn [map-of-all-user-maps]
> (into {}
> (doall
(Not likely to be a problem, but "into " and "doall" are redundant here.)
> (for [[username-as-key each-user-map]
> map-of-all-user-maps :when (is-current? each-user-map)]
> (conj updated-registry {(get each-user-map
> "username") each-user-map})))))))
I think that what you are doing here is something like the following?:
(into {} (keep #(is-current? %2) map-of-all-user-maps)
>
> (defn current-users [request]
> "The default action of this app. Add new users to the registry, and delete
> the ones that are more than 15 seconds old"
> (let [this-users-params (:params request)]
> (add-to-logged-in-registry this-users-params)
> (remove-old-registrants)
> (response (apply str (json/write-str @registry)))))
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