On Saturday, 27 July 2013 03:59:55 UTC+1, Jeremy Heiler wrote:
> On July 26, 2013 at 10:39:47 AM, Jürgen Hötzel
> (jue...@hoetzel.info<javascript:>)
> wrote:
>
> I did some memory profiling on a Clojure Application.
>
> I wondered why 361000 clojure.lang.Symbols exist.
>
> So I did some object browsing on the memory dump and found duplicate
> symbols. After checking the source:
>
> static public Symbol intern(String nsname){
> int i = nsname.indexOf('/');
> if(i == -1 || nsname.equals("/"))
> return new Symbol(null, nsname.intern());
> else
> return new Symbol(nsname.substring(0, i).intern(),
> nsname.substring(i + 1).intern());
> }
>
>
> I realized that interning of a symbol always returns a "new" Symbol object.
>
> If a symbol X is interned twice, shouldn't the second Symbol.intern(X)
> return the previous interned symbol object?
>
> It's not the symbol that's being interned, it's the string that represents
> the symbol. If you look at the equals() method for Symbol, you'll notice
> that it is using object equality (the double equals operator, ==) to
> compare the name of the symbol. So, if you have two symbols with the same
> name, they will be equivalent because they have the same string object
> internally. However, since each symbol can have its own metadata, the
> symbol objects cannot be interned as your are describing. Keywords fill
> that role, as Marshall mentioned.
>
You could plausibly intern all the symbols that are created with nil
metadata - a fairly common case?
Not sure if it would be worth it though. Symbols are already very
lightweight (assuming the underlying Strings are interned). You would win a
bit in terms of memory usage and quicker equality testing, at the expense
of having to maintain an interned symbol cache and perform lookups in it
all the time.
It would be interesting to see if metadata-less symbol interning sped up or
slowed down loading+compilation of Clojure code (which must surely be the
most important use case for symbols).
--
--
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.
