^:once is absolutely needed for lazy seqs, because it allows the
closed-over variables to get cleared while the lambda is *still running*,
rather than waiting for it to finish. You can see the difference in this
repl session:
user> (let [x (for [n (range)] (make-array Object 10000)), f (^:once fn* []
(nth x 1e6))] (f))
#<Object[] [Ljava.lang.Object;@402d3105>
user> (let [x (for [n (range)] (make-array Object 10000)), f (fn* [] (nth x
1e6))] (f))
; Evaluation aborted.
Of course you may need to tune the numbers to make sure it runs out of
space on your machine, but the point is that without ^:once, the lambda f
holds onto the head of x, in case f is called again. ^:once constitutes a
promise to only ever call it once, and so the sequence is cleaned up as
soon as possible. My example doesn't use LazySeq, but I hope you can see
how the same considerations apply there.
On Tuesday, February 18, 2014 9:39:06 AM UTC-8, pron wrote:
>
> lazy-seq marks it's supplied lambdata with ^{:once true} to prevent the
> memory leak described at the bottom of this page <http://clojure.org/lazy>
> .
> However, while going over the code for clojure.lang.LazySeq, I noticed
> that ever since this commit by
> Rich<https://github.com/clojure/clojure/commit/9253928ba2330b9929eb26577ba20047fb24c5de#diff-829faa850c65e040e132cd9243bf7ac2R42>,
>
> LazySeq doesn't extend AFn, but rather contains a reference to the lambda,
> fn, which it nullifies immediately after the first use, supposedly
> preventing any leaks caused by closed locals.
> So my question is, is ^{:once true} still necessary for lazy-seqs, or does
> this (pretty old) change to LazySeq make it redundant?
>
> Ron
>
>
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
