On July 26, 2013 at 10:39:47 AM, Jürgen Hötzel (juer...@hoetzel.info) 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.
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