On 14 July 2016 at 15:52, Alin Serdean <aserd...@cloudbasesolutions.com>
wrote:
> > > + flock(filep_pidfile, LOCK_EX);
> > >
> > Won't the above call block indefinitely if the lock has already been
> taken by
> > someone else? We don't want the behavior when someone starts a daemon
> > and it simply hang there.
> [Alin Gabriel Serdean: ] Hard to say from the MSDN documentation we could
> add "| LOCKFILE_FAIL_IMMEDIATELY" when calling it just to be sure.
> >
> >
> >
> > > +
> > > fatal_signal_add_hook(unlink_pidfile, NULL, NULL, true);
> > >
> > > fprintf(filep_pidfile, "%d\n", _getpid()); @@ -444,6 +481,10 @@
> > > make_pidfile(void)
> > > VLOG_FATAL("Failed to write into the pidfile %s", pidfile);
> > > }
> > >
> > > + flock(filep_pidfile, LOCK_SH);
> > > + /* This will remove the exclusive lock. The shared lock will
> remain */
> > > + flock(filep_pidfile, LOCK_UN);
> > >
> > I unsuccessfully tried to read MSDN documentation for the above behavior.
> > Can you please point me to the documentation which states that unlocking
> > once will move the lock from exclusive to shared?
> [Alin Gabriel Serdean: ]
> https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
> The part:
> "If the same range is locked with an exclusive and a shared lock, two
> unlock operations are necessary to unlock the region; the first unlock
> operation unlocks the exclusive lock, the second unlock operation unlocks
> the shared lock."
>
I see. Thank you. (I am blind!). I wonder whether we actually need the
exclusive lock then? If what we need is just shared lock, why not just take
it in the beginning? Would it have been possible to open the file in write
mode if someone had taken the exclusive lock in the first place?
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