[erlang-questions] C nodes and OTP

Michael Truog <>
Wed Jan 16 20:09:02 CET 2013


Hi

C nodes have been a non-intrusive way to communicate with Erlang nodes, and is used in jinterface for JVM communication.  So the main benefit of a C node is decoupling the startup of the C node code and the Erlang node code.  If you don't need the startup decoupled, I believe an Erlang port is a better choice.  If you want a simpler way of doing C-node-like integration, I have a project called CloudI (http://cloudi.org), which provides language integration (including Java) which avoids C nodes.

The scalability limitation to C nodes is related to the fully connected network topology that distributed Erlang makes and the use of the ERL_TICK message (limiting distributed Erlang to 50-100 nodes, unless you get a really fast network.... then perhaps 200).  So, avoiding C nodes is also avoiding scalability problems.

On 01/16/2013 09:44 AM, Robert Raschke wrote:
>
> Hi David,
>
> one potential pitfall with C nodes in general, regardless of pure message based or erl_rpc, comes when your C node does something time consuming. That is, your C node is not responding to ERL_TICK in a timely fashion. The connected Erlang nodes will then think that the C node has become disconnected.
>
> It is possible to recognise this situation from within the C node and explicitly reconnect to an Erlang node. I'm away from my work just now, but if you want an example, let me know and I'll send something round tomorrow.
>
> Alternatively, your C node can use threading to handle messages. That goes beyond my abilities ;-)
>
> Robby
>
> --
> Sent from a mobile device, please excuse the typos.
>
> On Jan 16, 2013 11:03 AM, "David Welton" < <mailto:>> wrote:
>
>     Hi
>
>     I'm trying to wrap my head around the "best" way to set up an
>     OTP-based system that comunicates with a C node.
>
>     My inclination so far is to set up a gen_server, and use handle_info/2
>     to deal with messages coming from the C node.
>
>     Looking at the C node example, it's all about messages, which seems to
>     be "the simplest thing that could possibly work", which is good.  I'm
>     wondering, though, if it makes more sense to try and call directly
>     into my gen_server's api with rpc, along the lines of what is being
>     done here:
>
>     http://stackoverflow.com/questions/4749693/can-i-get-erlang-otp-behaviors-in-c-nodes
>
>     Any other tips/tricks/best practices/pitfalls to avoid would be welcome.
>
>     Thanks,
>     --
>     David N. Welton
>
>     http://www.welton.it/davidw/
>
>     http://www.dedasys.com/
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