Good morning (at least from my part of the globe),
I spent a good chunk of time last night wondering why this chunk of code
kept exiting about a minute after being run:
----------------------------------------
(ns narcoleptic.server
(:require [aleph.http :as http]
[compojure.core :as compojure :refer [GET]]
[compojure.route :as route]
[ring.middleware.params :as params]))
(def handler
(params/wrap-params
(compojure/routes
(GET "/" [] "Hello World!")
(route/not-found "Not Found"))))
(def server (agent nil))
(defn -main []
(send-off server #(or % (http/start-server handler {:port 9000}))))
----------------------------------------
until I found
http://tech.puredanger.com/2010/06/08/clojure-agent-thread-pools/ which
explains that send-off pools die after a minute. Additionally, it looks
like all of the thread pools that aleph creates are marked as daemon
threads, so the main thread dies after the send-off, the send-off thread
dies after a minute and that leaves no non-daemon threads running, so
the JVM exits. Cool.
My question, then, is this: Is there a best practice for keeping a
thread open forever so that my server won't ever exit? I'd like to `lein
run -m narcoleptic.server` and see that it stays up as long as possible.
I've tried two solutions, but the first feels ike an awful lot of typing
for a language that usually has the right tools close at hand and the
second feels like a hack and doesn't play as nicely in a REPL
environment (but they both work):
(1)
----------------------------------------
(defn wait-until-stopped []
(let [stopped (promise)]
(add-watch server :stop-wait
(fn [key server old-state new-state]
(when (= new-state :stopped)
(remove-watch server :stop-wait)
(deliver stopped :ok))))
@stopped))
----------------------------------------
(2)
----------------------------------------
;; removed the agents code
(def stopped (promise))
(defn -main []
(http/start-server handler {:port 9000})
@stopped)
----------------------------------------
Am I super off in the woods here? Any help/pointers/sage advice
appreciated. Thanks!
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