[erlisp-devel] Re: SoC status update please

[Willem Broekema]

Joel Reymont:
> I think within Erlang nodes use a keep alive message to make sure
> they have not been split off. Quite often, though, you cannot detect
> if the foreign process exists.

To check whether a _node_ is still running and connected, monitor_node
can be used; from
<http://www.erlang.org/download/erlang-book-part1.pdf> page 98:

"If no connection exists, and monitor_node/2 is called, the system
will try to setup a connection and deliver a nodedown message if the
connection fails."

To check whether a _process_ is still alive, linking to it and
checking for the corresponding EXIT message is the way to go.

Dirk Gerrits:
> > I'm not sure if it matters if a node is dead or just split off.
> 
> Erlang doesn't make the distinction, does it?

>From the same page:

"The BIF [=built-in function] monitor_node(Node, Flag) can be used to
monitor nodes. An Erlang process evaluating the expression
monitor_node(Node, true) will be notified with a {nodedown, Node}
message if Node fails or if the network connection to Node fails.
Unfortunately it is not possible to differentiate between node
failures and network failures."


By the way, my experience with Erlang is mostly in trying to develop a
Gnutella client a few years ago. To the reasonable nice original
Gnutella protocol, many ill-specified ad-hoc extensions were added by
the existing clients. Implementing these extensions, which is
necessary in order to play well with the other clients, became less
and less interesting, so I never finished it. Although I still find
Erlang interesting, these days I'm more interested in Common Lisp.

- Willem