[erlang-questions] make_ref bug or feature?

Serge Aleynikov saleyn@REDACTED
Fri Mar 27 12:57:41 CET 2009

Since a reference contains a node name, it's considered unique in a 
distributed setup when nodes have different names (or within a single 
non-distributed node).  When two shells are started this way, since they 
are not aware of each other and can't see each other's references, is it 
a problem that their values are identical?


Joe Armstrong wrote:
> I got a question from Ivo Danihelka about make_ref().
> Isn't make_ref() supposed to generate "an almost unique reference" the
> manual says
>     "Returns an almost unique reference.
>      The returned reference will re-occur after approximately 2^82
> calls; therefore it is unique enough for practical purposes."
> If I start two erlang shells and evaluate the following in both shells:
> 1> io:format("~p~n",[term_to_binary(make_ref())]).
> <<131,114,0,3,100,0,13,110,111,110,111,100,101,64,110,111,104,111,115,116,0,0,
>   0,0,34,0,0,0,0,0,0,0,0>>
> They *both* print the same thing - this violates the principle of
> least astonishment.
> (I thought I'd have to start 2^82 shells :-)
> Is this a bug or a feature?
> /Joe
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