User-space notification of process end

User-space notification of process end

[Glen Turner]

Hi,

I am writing a application which needs to know fairly
promptly if a daemon has died.  I'd prefer not to
alter the daemon source code or to run the program
as a non-daemon child of a daemon watcher process.

I tried using fnctl(..., F_NOTIFY, ...) as
follows

  f = open("/proc/123", O_RDONLY);
  signal(SIGIO, handler);
  fcntl(f, F_NOTIFY, DN_DELETE | DN_RENAME);
  F_ZERO(&f_set);
  F_SET(f, &f_set);
  select(1, NULL, NULL, &f_set, NULL);

hoping I'd see the /proc/<processid>/* files being
removed at process end.

But procfs doesn't seem to support fnctl(.., F_NOTIFY, ...)
for parameters other than DN_ACCESS.  This doesn't seem
to be limited to my code (the dnotify program, which has
much better signal handling, has the same behavior).

Suggestions, particularly ones which don't require polling
for the existence of the watched process, are welcome.

uname -r says 2.4.22-1.2149.nptl, which is the latest
Fedora Core 1 kernel.  I'm willing to try 2.6 if that
supports F_NOTIFY on /proc.

Thanks,
Glen

-- 
Glen Turner         Tel: (08) 8303 3936 or +61 8 8303 3936 
Network Engineer          Email: glen.turner@aarnet.edu.au
Australian Academic & Research Network   www.aarnet.edu.au

Re: User-space notification of process end

[Paul Jackson]

> I am writing a application which needs to know fairly promptly if a
> daemon has died.  I'd prefer not to ... run the program as a non-daemon
> child of a daemon watcher process.

Why not a watcher process, if I may ask.  That is, I'd be tempted to
stash a copy of the daemon's executable, and in place of the original
executalbe put a piece of code that fork/exec'd the stashed copy, waited
for the exit, and notified you as need be.

The available operations on files in the /proc file system tend to
be a very limited subset of those on regular files; so I am not
surprised that F_NOTIFY didn't work.

-- 
                          I won't rest till it's the best ...
                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373