On 11 July 2010 12:38, Jeffrey Schwab <[email protected]> wrote:
> Is it safe to alter an atom while iterating that atom's value? It seems to
> work as I would expect, but am I just getting lucky (and are there
> concurrency issues)?
>
> user=> (let [a (atom #{1 2 3 4 5})]
> (doseq [x @a] (prn @a) (swap! a disj x)))
Whenever you deref an atom (using @), you're getting a static value of
the atom at that instance in time.
Your example code is logically equivalent to:
(let [a (atom #{1 2 3 4 5})]
(doseq [x #{1 2 3 4 5}]
(prn @a)
(swap! a disj x)))
You're not iterating over the atom per se; you're just iterating over
the value of the atom at that point in time.
So yes, it's safe. This is one of the benefits of Clojure concurrency
constructs - you're not changing the value inside, you're just
pointing to a different value.
- James
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