Re: graceful restart under runit

[prj@po.cwru.edu (Paul Jarc)]

Dražen Kačar <dave@fly.srk.fer.hr> wrote:
> PIDs are not recycled fast in practice, so that would have to be
> good enough.

They certainly are recycled fast in practice, although maybe not
often.  For example, OpenBSD can assign PIDs in random order instead
of sequentially, so a PID has a chance of being reused for the very
next process after it exits.  The same problem can hit any OS if it
spawns short-lived processes at a high rate.

For me, at least, it's well worth using poll()/select() to avoid this
risk.  It's a one-time task for the programmer, but PID recycling is a
constant danger for every user.

> Somewhat unportable guarantee could be obtained via /proc.  You know the
> PID, so you stop the process via /proc or ptrace() or whatever is
> available for debuggers (something will be available), check that the PID
> is associated with the correct executable via /proc,

Even if it's the right program, that doesn't guarantee it's the right
process.  This seems like more work than poll()/select(), with worse
results.


paul