Failed to create - mailbox is locked

[Bron Gondwana]

On Thu, Sep 3, 2015, at 23:50, Ken Murchison wrote:
> On 09/03/2015 08:42 AM, Bron Gondwana wrote:
> > IOERROR: failed to create fastmail.com!user.REDACTED.#calendars (Mailbox is locked)
> >
> > We get these occasionally, and I wondered why until just now, when I remembered...
> >
> > The initial CREATE or RENAME lock.. it's a mboxname_lock EXCLUSIVE, and it's taken with nowait, and error if exists.  It needs to, because the source mailbox is locked, and you need to break a lock loop if you issued rename A => B and rename B => A in parallel.
> >
> > So it was assumed as being not a problem, because you'd never try to create the same name twice concurrently.  The name didn't exist before, so nobody will be looking at it.
> >
> > When I say "it was assumed", I mean that I assumed.  In 2009 some time.
> >
> > But that's not true when you're autocreating the same name when you try to read something.  Anything.
> >
> > In fact, the way that the parser works, you wind up doing it for any http request.  So you get a race between two processes, one loses, logs this.
> >
> > We should probably fix this :)
> >
> > Bron.
> 
> 
> Doesn't the current code check to see if the calendar-home-set mailbox 
> (and others) exist before trying to CREATE them?

Yeah, but it's racy.  If two processes try at the same time, then they'll both go for the exclusive lock with a non-blocking request, and one will miss out.

Bron.


-- 
  Bron Gondwana
  brong at fastmail.fm