Re: How to communicate with a running external process with given PID?

[Kevin Rodgers <kevin.d.rodgers@gmail.com>]

On 7/20/13 3:06 AM, Thorsten Jolitz wrote:
> say I want to call another program (more exactly, another Lisp program
> that is not Emacs Lisp) from an Emacs Lisp program.
>
> My special requirement is that I don't want to start a new Emacs
> subprocess, but want to communicate with an existing (running) process.
> And there maybe several running instances of this program at the same
> time, so I want to communicate with one existing (running) process with
> a given PID.
>
> Now there is splendid support in Emacs for communicating with other
> programs, but always based on the assumption that Emacs starts and
> controls a new subprocess.
>
> There is chapter 37.12 "Accessing Other Processes" in the Elisp manual,
> and I can do successfully
>
> ,-------------------------
> | (process-attributes PID)
> `-------------------------
>
> to receive a lot of information about the process I want to communicate
> with.
>
> But what then? Where are the (e.g.) `process-send-string' or
> `process-send-region' functions for external processes I could use to
> communicate with my external program?
>
> I could run a server in the external lisp program and use a
> network-connection-object to send http-requests (e.g. with the help of
> emacs-request.el) via TCP - but that seems to be total overkill for my
> requirements.
>
> I just want to use a running external process with a given PID in a
> similar way I would use (a)synchronous processes created from Emacs with
> `call-process' or `start-process'. How can I do that?
>
> Maybe there is an obvious answer to this question that I don't see.

Since Emacs did not start the external process, it does not have access to its 
standard input stream -- unless your OS provides a way to do that (e.g. via a
special /dev file).

How would you communicate with the external process, from any other program?

-- 
Kevin Rodgers
Denver, Colorado, USA