It looks to me like the future sees the re-binding whereas the native
thread does not! Like you, I'd expect the same behaviour from these 2
lines...Can anyone shine some light on this? I'm suspecting it has
something to do with the thread pooling that is going on but I've got
nothing to base this on...
Jim
On 03/08/12 08:49, Daniel Silén wrote:
Hi!
I am new to the language, and at the moment playing around with
concurrent-constructs as presented in a series on Clojure concurrency
at pluralsight.com (by Chraig Andera).
When playing with thread-local redefinitions of vars via the
binding-macro, I found an unexpected behavior:
A future is used to create a background-thread, and I would expect it
to behave the same way as when creating an explicit java thread,
however it doesn't.
If I rebind a var's value it receives the new value - but it
shouldn't, because it is in another thread, right?!
Example:
(def ^:dynamic foo :fooval)
(def p (promise))
(def p2 (promise))
(binding [foo :newval]
(future (deliver p foo))
(.start (Thread. #(deliver p2 foo)))
(println "in future: " @p) ; expected value of @p :fooval, actual
:newval
(println "in java thread: " @p2)
(println "in binding: " foo))
(println "outside binding: " foo)
produces (in clojure 1.4.0):
user=> in future: :newval
in java thread: :fooval
in binding: :newval
outside binding: :fooval
nil
I would expect the future-row to return the same as the
java-thread-row, :fooval.
I would love to hear an expert-explanation... What did I do wrong? :)
Kind regards
Daniel Silén
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