give local pid and node name, how to convert to remote pid? - erlang

Question

A remote pid registers its "local pid" and "its node" name has been registered into mnesia table. If another node's pid fetch the above "local pid<0.xxx.xxx>" and node name, how to convert to remote pid<xxx.xxx.xxx>.

Answer 1

I don't really see WHY you have to do anything special at all. Here I will create a mnesia table running on l#renat and r#renat and write and read pids from the respective nodes and show their is no need to "convert" the pid as Erlang's distribution mechanism automatically take care of it. It will be a bit long to get it all working.
First on node l#renat we connect or the other node and create our mnesia schema:
Eshell V5.9.1 (abort with ^G)
(l#renat)1> net_adm:ping(r#renat).
pong
(l#renat)3> mnesia:create_schema([node()|nodes()]).
ok
(l#renat)5> mnesia:start().
ok
On node r#renat we have just started mnesia:
Eshell V5.9.1 (abort with ^G)
(r#renat)1> mnesia:start().
ok
On node l#renat we then create a table and insert an entry containing a local (to l#renat) pid:
(l#renat)6> mnesia:create_table(local, [{attributes,[node,pid]},{ram_copies,[node()|nodes()]}]).
{atomic,ok}
(l#renat)8> mnesia:transaction(fun () -> mnesia:write({local,node(),self()}) end).
{atomic,ok}
Note that I have not defined the records but am explicitly reading/writing the record tuples. You can do that, but it is best to use records. Now on node r#renat we can read the same record:
(r#renat)10> {atomic,[Lr]} = mnesia:transaction(fun () -> mnesia:read(local, l#renat) end).
{atomic,[{local,l#renat,<5893.37.0>}]}
(r#renat)11> node(element(3, Lr)).
l#renat
(r#renat)12> mnesia:transaction(fun () -> mnesia:write({local,node(),self()}) end).
{atomic,ok}
and we see that the pid refers to a process on another node(), node l#renat. We have then added a record to the table containing a local (to r#renat) pid. If we then read that record on node l#renat we see that it contains a pid of a process on node r#renat:
(l#renat)13> {atomic,[Rp]} = mnesia:transaction(fun () -> mnesia:read(local, r#renat) end).
{atomic,[{local,r#renat,<6007.85.0>}]}
(l#renat)14> node(element(3,Rp)).
r#renat
So we see that a "conversion" is not necessary.
In fact any form of "conversion" is in fact totally meaningless. A pid refers to a specific process on a specific node so trying to convert it has no meaning. It is an atomic data type. And even if you could convert it you have no idea of what process it would actually refer to, if any.