On Tue, Nov 23, 2010 at 11:45 PM, HiHeelHottie <[email protected]> wrote:
>
> Does anybody know of an implementation for a priority queue that can
> be used for scheduling events in the future? I would like to put a
> map associated with a timestamp into the queue and be able to pull out
> all maps at or before a given time in order.
That's something you can slap together in a few minutes.
user=> (def sched (ref (sorted-map )))
(def jobber (agent nil))
(defn schedule-job!* [time runnable]
(dosync
(alter sched assoc time runnable)))
(defn- next-job-time []
(key (first @sched)))
(defn- do-next-job! []
(dosync
(when-let [[k v] (first @sched)]
(alter sched dissoc k)
(send-off jobber (fn [_] (v) nil)))))
(defn- job-runner []
(loop []
(if-not (empty? @sched)
(if (> (System/currentTimeMillis) (next-job-time))
(do-next-job!)))
(Thread/sleep 10)
(recur)))
(doto (Thread. job-runner)
(.setDaemon true)
(.start))
(defn schedule-job-after!* [delay runnable]
(schedule-job!* (+ (System/currentTimeMillis) delay) runnable))
(defmacro schedule-job! [time & body]
`(schedule-job!* ~time (fn [] ~...@body)))
(defmacro schedule-job-after! [delay & body]
`(schedule-job-after!* ~delay (fn [] ~...@body)))
(schedule-job-after! 10000
(println "foo"))
(schedule-job-after! 30000
(println "bar"))
(schedule-job-after! 20000
(println "baz"))
{1290576825292
#<user$eval2986$fn__2987 user$eval2986$fn__2...@1ef2fd3>,
1290576835296
#<user$eval2994$fn__2995 user$eval2994$fn__2...@1d5e94f>,
1290576845294
#<user$eval2990$fn__2991 user$eval2990$fn__2...@24b943>}
user=>
foo
baz
bar
The last three lines will print at ten-second intervals and may not
appear in the same console as your user=> prompt depending on how your
REPL/IDE handles asynchronous printlns. With NetBeans they'll appear
in *out* instead of Repl (for sure) and in slime in the inferior-lisp
buffer (I think).
This could be reworked to use java.util.Date but the basic
architecture would remain the same.
You'll need to (shutdown-agents) during shutdown of any application
where you use this if you don't want the JVM to linger as a zombie
process.
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