I am fairly new to Clojure, and new to the JVM, so I do not know how to diagnose a dying app.
I have a very simple app that tries to keep track (in memory) of who is logged in. I'll show the code below. I compiled this app and uploaded it to my server and launched it like this: who-is-logged-in-1.0.1-standalone.jar 40000 </dev/null >/dev/null 2>&1 & This ran for a day or two, and then it died. I restarted it, and it ran another day or 2, and then it died. I just restarted it so you might be able to see its output here: http://www.tailormadeanswers.com:40000/ What you see is from some Javascript, which works when people log into a site like this: http://www.wpquestions.com/ On that site, the Javascript sends an Ajax ping every 10 seconds. The Clojure app remembers everyone who has sent a ping during the last 15 seconds. I don't think this has ever been more than 30 people, so I doubt that I am at risk of exhausting the memory. If the app is running, you can see some usage stats here: http://www.tailormadeanswers.com:40000/show-resources I have not yet added any security to the app, so there is a chance that someone is shutting it down with spam. (I just got this app up last week, and was planning to add security checks this week). I do not know much about programming for the JVM, so I am curious, how do I diagnose this? I could add some logging, but what should I log? What should I be looking for? My project.clj looks like this: (defproject who-is-logged-in "1.0.1" :description "When users arrive at a site like wpquestions.com, and then log in, the Javascript on that site should do 2 things: ping this software to let us know that user has logged in, and also ping this software to get some info about who else is logged in. The Javascript on the site should be able to take the data this software sends and turn it into a meaningful list of logged in users. Version: 1.0.1: since the output needs to be consumed by Javascript as JSON, I'm making some changes in the way the registry outputs." :dependencies [[org.clojure/clojure "1.3.0"] [net.cgrand/moustache "1.1.0"] [ring "1.1.5"] [ring/ring-jetty-adapter "1.1.5"] [org.clojure/data.json "0.2.0"]] :main who-is-logged-in.core :jvm-opts ["-Xmx4000m"]) 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) 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 {}) (swap! registry (fn [map-of-all-user-maps] (into {} (doall (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}))))))) (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))))) -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
