[erlang-questions] data sharing is outside the semantics of Erlang, but it sure is useful
Thu Sep 17 08:00:34 CEST 2009
On Sep 17, 2009, at 2:46 PM, Witold Baryluk wrote:
> It is quite strange to anybody, that for example time complexity
> (and memory also as sharing is lost) of algorithm are different in
> 1) we built data structure D, and execute algorithm a(D)
> 2) we build data structure D, send it to P, which then executes a(D).
My message explicitly said that I thought that Erlang should
*PRESERVE* sharing, including in message passing. You didn't
need to persuade me of something I already argued for.
The point at issue, as I understood it, was an "OPTIMIZATION",
namely INTRODUCING sharing. For example, if memory serves me
correctly, whenever the Logix implementation of Flat Concurrent
Prolog successfully executed a test X == Y, it smashed one of
them to refer to the other. That's run-time introduction of
sharing. The reason why Logix did that was that they didn't
_have_ atoms, only strings, in order to avoid having to lock
a centralised symbol table. But they wanted strings to _act_
rather like atoms.
within a during message
preserve sharing YES YES
introduce sharing NO NO
 This is what Erlang does now.
 This is a change, and it's going to be tricky to do it
without slowing "normal" cases down.
And I'm counting term_to_binary/binary_to_term here,
because of their use when messages are passed over a wire.
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