Meyer, OO and concurrency

[Ulf Wiger]

Den 2005-07-14 18:23:42 skrev David Hopwood  
<david.nospam.hopwood@REDACTED>:

> Peter-Henry Mander wrote:
> Hi Gurus,
>  Sorry but I've got to stick my oar in.
>  I've found that modelling a OO system in Erlang recovers the original
> concept of objects as concurrent actors.
>
>  Almost, but:
>   - Erlang does not garbage-collect processes when they are waiting
>    unconditionally for a message that can never be sent.

This was discussed recently in comp.lang.functional and
some other newsgroups. I think what came out of the discussion
was that a process never becomes unreachable in Erlang, and
thus, there is no way to determine that a process is waiting
in vain. Besides, I believe that it's quite beneficial for
debugging that a hanging process isn't automatically removed
before anyone has a chance to inspect it.


>   - Erlang Pids are forgeable, and it is possible to enumerate
>     the Pids of all processes (which was prohibited in actor
>     systems).

... part of the reason why processes are always reachable.
Also a great feature during debugging.


>   - processes in Erlang implementations, although they are more  
> lightweight than threads, are still a bit too heavyweight to be
> used in the same way as objects.

Agreed. This is one reason why mapping OOD to Erlang is not
such a great idea. For different types of object, you need to
choose different implementations in Erlang. Every type of
object can't reasonably be mapped onto a process.

/Uffe