Hi Jon, I have logged your patch into the issue tracker, 3546; http://subversion.tigris.org/issues/show_bug.cgi?id=3546
Gavin On 28/11/2009, at 06:53 , Jon Foster wrote: > Hi, > > This fixes the race condition where two svnsync processes can lock > the repository at the same time (as noticed by Stefan Sperling > earlier today). I wanted to do this without changing the RA layer, > so that it can work with older servers. > > Since the RA layer doesn't have a test-and-set primitive (other > than a commit!), some raciness is inevitable. This patch fixes the > dangerous race, but introduces a much less dangerous race. With > this patch, two "svnsync" processes trying to lock the repository at > the same time might both fail to get the lock. To mitigate this, > both processes will sleep for a random amount of time before > retrying. This should reduce the chance of them staying in lock-step > and repeatedly failing. (Hopefully the chance becomes negligible). > > This doesn't conflict with my --use-external-locking patch from > earlier today; they change different parts of the code and have > different use-cases. > > [[[ > Fix race condition that allowed two svnsync processes to get the lock > at the same time. > > * subversion/include/svn_props.h: > (SVNSYNC_PROP_PRE_LOCK_PREFIX): New define. > > * subversion/svnsync/main.c: > (get_local_host_name, generate_moderately_random_number, > try_get_lock): New functions. > (get_lock): Rewritten. > > Found by: stsp > Jon Foster <jon.fos...@cabot.co.uk> > (Independently discovered) > Patch by: Jon Foster <jon.fos...@cabot.co.uk> > ]]] > > Apologies for the .zip format - my mailserver is blocking outgoing > .patch files. > > Kind regards, > > Jon Foster > > > ********************************************************************** > This email and its attachments may be confidential and are intended solely > for the use of the individual to whom it is addressed. Any views or opinions > expressed are solely those of the author and do not necessarily represent > those of Cabot Communications Ltd. > > If you are not the intended recipient of this email and its attachments, you > must take no action based upon them, nor must you copy or show them to anyone. > > Cabot Communications Limited > Verona House, Filwood Road, Bristol BS16 3RY, UK > +44 (0) 1179584232 > > Co. Registered in England number 02817269 > > Please contact the sender if you believe you have received this email in > error. > > ********************************************************************** > > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please visit http://www.messagelabs.com/email > ______________________________________________________________________<svnsync-two-step-locking.zip>
