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

["Pascal J. Bourguignon" <pjb@informatimago.com>]

Thorsten Jolitz <tjolitz@gmail.com> writes:

> Hi List, 
>
> 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.
> Would be nice. 

Ok, I'll bit the bullet: the only communication channel available to
you, a-priori, knowing only the process ID, is the kill(2) syscall.
And you're lucky, you can send more than one bit of information with
each kill call!

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
A bad day in () is better than a good day in {}.  
You know you've been lisping too long when you see a recent picture of George 
Lucas and think "Wait, I thought John McCarthy was dead!" -- Dalek_Baldwin