[erlang-questions] data sharing is outside the semantics of Erlang, but it sure is useful

[Mikael Pettersson]

Ulf Wiger writes:
 > Mikael Pettersson wrote:
 > >  
 > > Erlang's default memory model doesn't allow same-node processes to
 > > share memory(*), so you will lose sharing in message sends.
 > 
 > Yes, but there are two levels of sharing here.
 > 
 > 1. The sharing of terms across processes, as with large binaries
 > 2. The relative sharing within the term itself.
 > 
 > The latter could be preserved using a sharing-preserving copy.
 > As this is invariably more expensive than the current copying
 > algorithm when there is no sharing to preserve (likely a very
 > common case), it is reasonable that this isn't the default.
 > 
 > The problem today is that you cannot make a sharing-preserving
 > copy between processes at the Erlang level even if your life
 > depended on it, and in some cases, this may indeed be the case,
 > figuratively speaking. Some data structures simply cannot be
 > passed in a message or in a spawn, since the loss of sharing
 > leads to a memory explosion.

So a sharing-preserving term_to_binary might fix the worst
problems, even if it requires some non-default option and
requires users to explicitly wrap and unwrap parts of messages?

Just trying to see if this is something worth pursuing or not.

/Mikael