Erik that's pretty! But be careful about go-loops and closed channels. This
will recur infinitely if events-ch is closed (it will continuously return
nil)
(defn invoke-after-uninterrupted-delay
([period events-ch f]
(invoke-after-uninterrupted-delay period events-ch f []))
([period events-ch f & args]
(async/go-loop []
(let [[v p] (async/alts! [(async/timeout period) events-ch])]
(when v
(if (= p events-ch)
(recur)
(apply f args)))))))
will allow the go-loop to return when the channel is closed.
On Monday, December 1, 2014 8:33:10 PM UTC-5, Erik Price wrote:
>
> Coincidentally, we recently wrote code to do something very similar. The
> following function will invoke f after period milliseconds, unless a
> value is sent on events-ch, in which case the timeout is reset (and
> starts counting down again):
>
> (defn invoke-after-uninterrupted-delay
> ([period events-ch f]
> (invoke-after-uninterrupted-delay period events-ch f []))
> ([period events-ch f & args]
> (async/go-loop []
> (let [[_ p] (async/alts! [(async/timeout period) events-ch])]
> (if (= p events-ch)
> (recur)
> (apply f args))))))
>
> e
>
>
> On Mon, Dec 1, 2014 at 6:50 PM, Brian Craft <[email protected]
> <javascript:>> wrote:
>
>> That version has the unfortunate behavior that (func) can be interrupted
>> if (event) is called while it is running. Here's another version using an
>> agent:
>>
>> (defn queue-with-delay2 [period func]
>> (let [q (agent nil)]
>> (fn []
>> (send-off q (fn [t]
>> (when t
>> (future-cancel t))
>> (future (Thread/sleep period) (send-off q (fn [_]
>> (func) nil))))))))
>>
>> Running with a sleep to see that (func) is not canceled by subsequence
>> (event) calls:
>>
>> (def event (queue-with-delay2 2000 #(do (println "running") (Thread/sleep
>> 2000) (println "ending"))))
>>
>> Oddly, if calling (event) between "running" and "ending" messages, the
>> repl will stack-overflow on the return value. No idea what that's about.
>> But, running like this is fine:
>>
>> (do (event) nil)
>>
>>
>>
>>
>>
>> On Monday, December 1, 2014 1:37:56 PM UTC-8, Brian Craft wrote:
>>>
>>> I have need to perform an action when a series of events is quiet for
>>> some period. That is, if one event arrives an action is queued to execute
>>> after some timeout. If a second event arrives the timeout is reset, and
>>> so-forth.
>>>
>>> The following code seems to work, however I'm wondering if calling
>>> 'future' from 'swap!' is a bad idea (side effecting), and if there's a
>>> better way.
>>>
>>> (defn queue-with-delay [period func]
>>> (let [f (atom nil)]
>>> (fn []
>>> (when @f
>>> (future-cancel @f))
>>> (swap! f (fn [_] (future (Thread/sleep period) (func)))))))
>>>
>>>
>>> Use like
>>>
>>> (def event (queue-with-delay 2000 #(println "running")))
>>> (event)
>>> (event)
>>> (event) ; pause 2 sec
>>> "running"
>>>
>>>
>>>
>>> --
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>
>
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