This approach works for the simple case but gets cumbersome it a more
realistic loop with several timeouts and conditional logic. For
example, here is a reduced use case which I am using my go-loop macro I
posted earlier:
(let [heads? (fn [] (> (rand) 0.5))
heads-time-out 10000
loop-time-out 100]
(go-loop [stop-timeout]
(if (heads?)
(do
(println "HEADS! I'm doing some stuff...")
(sleep heads-time-out stop-timeout)
(println "doing some more stuff"))
(sleep loop-time-out stop-timeout))))
The problem, as I see it, is that with your approach the channel from
each alts! needs to propagated to the end of the loop. So, I would
either need to restructure the code above to do that or use an atom and
have the go-loop/sleep macros take care of it for me.
-Ben
On 7/17/13 1:31 PM, David Nolen wrote:
Why not the following?
(let [stop (chan)]
(go (loop []
(println "Hello World!")
(let [[v c]] (alts! [(timeout 10000) stop])]
(if (= c stop)
:done
(do (println "I'm done sleeping, going to recur now...")
(recur)))))))
On Wed, Jul 17, 2013 at 2:47 PM, Ben Mabey <b...@benmabey.com
<mailto:b...@benmabey.com>> wrote:
Hi all,
In a number of places where I'm trying core.async I have run
across the pattern of having a loop inside a go block with some
timeouts in the loop body. Contrived example:
(go
(while true
(println "Hello World!")
(<! (timeout 10000))
(println "I'm done sleeping, going to recur now...")))
In situations like these I almost always want to be able to stop
the loop and prematurely stop the timeouts. Using alt! we can
easily handle the need of stopping the timeout. Stopping the
overall loop is easy as well but I can't seem to do it without the
use of an atom. Here are some macros I've come up with using a
channel, an atom, and an additional go block:
https://gist.github.com/bmabey/6023231
Is there a better way to do this that doesn't involve an atom? If
we had a `closed?` fn for channels one could write:
(let [stop (chan)]
(go
(while (not (closed? stop))
(println "Hello World!")
(alts! [(timeout 10000) stop])
(println "I'm done sleeping, going to recur now...")))
stop)
This seems ideal and a good use case for adding some sort of
function to detect termination. Thoughts?
Thanks,
Ben
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