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Re: Feature suggestion: server sockets

From: Helmut Eller
Subject: Re: Feature suggestion: server sockets
Date: Tue, 19 Feb 2002 22:33:02 +0100

address@hidden wrote:

> This is a useful feature, and a clean Lisp interface.
> I see a couple of possible gaps in the implementation, though.
> Doing this from Emacs itself is cleaner than running an actual
> subprocess like emacsserver to do the job.  But the subprocess runs
> all the time, in parallel with Emacs, while this code seems to be able
> to accept a server connection only inside wait_reading_process_input.
> If Emacs is running a Lisp program for a long time, it may go for a
> long time without ever calling wait_reading_process_input.  This could
> conceivably mean that Emacs takes too long to respond and the request
> fails.
> Can you make connection acceptance happen in response to a signal
> such as SIGIO, or make it happen in an alarm that happens frequently?
> (Such as the one used to poll for available terminal input.)
> The actual running of the filter function would have to wait until
> wait_reading_process_input, of course.  Something like this already
> happens with sentinels, I recall.

I think this is not necessary.  Connection requests are queued by the
OS; accept just takes the first established connection out of the
queue.  A request only fails if the queue is already full.

> One other point: this seems to be designed to work with PF_INET
> sockets only.  If you look at emacsclient, you'll see it uses either a
> PF_UNIX socket or SYSVIPC.  To make server sockets replace
> emacsserver, they would have to support both PF_UNIX sockets and
> SYSVIPC (unless SYSVIPC is obsolete nowadays and all systems support
> sockets).

I modified the code to work with Unix domain sockets.
open-server-socket takes now 3 arguments: NAME, PROTOCOL and
PORT-OR-PATHNAME.  Protocol is either 'inet or 'unix.

Supporting SYSVIPC would be a lot of work, because SYSVIPC uses a
different API, e.g. msgrcv/msgsnd where sockets use read/write.  I
think SYSVIPC is not worth the trouble.


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