woops should actually be
(go-loop []
(let [[v c] (alts! [(timeout period) events-ch])]
(if (= c events-ch)
(when v
(recur))
(apply f args))))
the timeout returns nil....
On Wednesday, December 3, 2014 3:47:35 PM UTC-5, Erik Price wrote:
>
> Thank you for calling my attention to this possibility!
>
> e
>
> On Wed, Dec 3, 2014 at 2:49 PM, Dylan Butman <dbu...@gmail.com
> <javascript:>> wrote:
>
>> 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 <craft...@gmail.com> 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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