Re: How to communicate with a running external process with

[Yuri Khan <yuri.v.khan@gmail.com>]

On Tue, Jul 23, 2013 at 2:59 PM, Thorsten Jolitz <tjolitz@gmail.com> wrote:

> Assume there are 2 otherLisp processes up and running and 2 Emacs
> processes, and you want to communicate from otherLisp with PID 5555 to
> Emacs with PID 6666.

First, decide which program is the server and which is the client. A
server, roughly speaking, is the process that first establishes the
channel of communication — creates a pipe, a Unix socket, or listens
on a TCP port. Clients then have to know the pipe path/filename, the
Unix socket path, or the IP address and TCP port, in order to connect
to the server. Once the connection by client is established, both
server and client have a file descriptor and can communicate just by
writing into it.

If you have two instances of the server, they have to listen on
different pipes, Unix sockets (by path/name), or, in case of TCP, the
<IP address:port> pairs have to be distinct. Thus, the clients will be
able to connect to the server they want, by knowing the specific
server pipe or Unix socket path or IP address and TCP port.

The process ID just never enters the picture. (Although, if you
control the server, you can make up a convention that, e.g., the
server always listens on the Unix socket with the path
/var/run/your_server_name.$PID.)