Re: graceful restart under runit

[Gerrit Pape <pape@smarden.org>]

On Thu, Nov 16, 2006 at 04:24:46PM +0100, Dra?en Ka?ar wrote:
> Alex Efros wrote:
> > On Wed, Nov 15, 2006 at 12:47:54PM +0100, Dra?en Ka?ar wrote:
> > > Say I have a TCP server which listens on incoming connections on some TCP
> > > port. Occasionaly I'd like to install and run a new version of the server
> > > executable. Server source is under my control, for all intents and
> > > purposes.
> > [...] 
> > > Is there a way to get around this?
> > 
> > Probably you can just fork() after receiving SIGUSR1 and exit from parent
> > leaving child to process existing connection.

Yes.

> Servers which use process per connection do something like that already
> (the parent process signals the children, exits and leaves them to finish
> sessions and then they exit too).
> 
> However, there are multithreaded monsters which can't do that. fork()
> replicates just the calling thread[1], so it's not an option and exit()
> will terminate all threads (ie. all sessions).

Hm, even though I too dislike "multithreaded monsters", we could add
some detach support to runsv, e.g. the patch below.  You can test this
with

 $ printf f >./supervise/control

After this, runsv forgets about the child, and considers the service to
be terminated; custom/f, if it exists, will be run before detaching.

Regards, Gerrit.


Index: src/runsv.c
===================================================================
RCS file: /cvs/runit/src/runsv.c,v
retrieving revision 1.26
diff -u -r1.26 runsv.c
--- src/runsv.c 24 Jul 2006 21:01:37 -0000      1.26
+++ src/runsv.c 17 Nov 2006 12:58:34 -0000
@@ -359,6 +359,15 @@
     update_status(s);
     if (! s->pid) startservice(s);
     break;
+  case 'f': /* forget, detach */
+    if (! s->pid) break;
+    custom(s, c);
+    s->pid =0;
+    s->state =S_DOWN;
+    s->ctrl =C_NOOP;
+    pidchanged =1;
+    update_status(s);
+    break;
   case 'a': /* sig alarm */
     if (s->pid && ! custom(s, c)) kill(s->pid, SIGALRM);
     break;