Yin Wang wrote: > Hi Howard, > > Sorry I am replying a very old email below that > you send in last April. Terence is a colleague > of mine and we are still working on the project. > I hope to understand the problem better. > > When you said "While we can control the order of > lock acquisition in the OpenLDAP code, we have no > control over it in the BerkeleyDB layer", do you > mean the (possible) deadlock comes from BerkeleyDB > or it is because of the interaction of OpenLDAP > and BerkeleyDB? If it is the latter case and I > assume BerkeleyDB is deadlock-free, I don't understand > why using such a library could cause deadlocks. > > Your help would be greatly appreciated. Since you say you're working on a research project, you shouldn't assume anything. You should do some actual research. The BerkeleyDB lock system is fully described in their documentation. Read it. If you have questions that aren't addressed by the BerkeleyDB docs you can ask those, but I don't have time to answer questions about things that are already well documented. > > Yin Wang > Research Assistant > EECS Department, University of Michigan > > >> -----Original Message----- >> From: Howard Chu [mailto:hyc@openldap.org] >> Sent: Thursday, April 19, 2007 5:32 PM >> To: Kelly, Terence P >> Cc: Project(a)openldap.org >> Subject: Re: deadlocks in OpenLDAP >> >> Kelly, Terence P wrote: >> >>> Hi, >>> >>> I'm a researcher with interests >>> in concurrent programming issues. I'm >>> writing with a question about deadlocks >>> in OpenLDAP code. >>> >>> Based on the OpenLDAP issue tracking system, >>> I gather that deadlocks involving circular >>> wait for locks have occurred or have been >>> suspected in slapd. >>> >>> In principle it's possible to avoid deadlock >>> by consistently acquiring locks in a defined >>> order, but in practice this can be inconvenient >>> or impossible. >>> >>> Can you give me some intuition for why it's >>> hard to prevent deadlocks in slapd? Has >>> your experience with deadlocks in OpenLDAP >>> software given you any generic insights >>> into deadlock and how (not) to avoid it? >>> Would your insights apply to other >>> software in addition to slapd? >>> >>> Many thanks in advance for any wisdom you >>> can share! Long editorials and brain dumps >>> are particularly welcome. >>> >>> -- Terence >> For OpenLDAP the problem is that there are two layers of locking systems >> >> in use - the OpenLDAP code and the BerkeleyDB code. While we can control >> >> the order of lock acquisition in the OpenLDAP code, we have no control >> over it in the BerkeleyDB layer. As such, the usual approach of strictly >> >> ordering locks doesn't work here. -- -- Howard Chu Chief Architect, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/