Yes. I was digging a bit in curator code and thinking about how can I implement this. If I would be able to somehow intercept creation of lock nodes, I could build GC/heartbeat logic around the lock by "installing" appropriate hooks.
One idea is that lock would accept a kind of LockNodeFactory, which would be responsible for creating actual zookeeper nodes. LockInternals.attemptLock() would delegate construction to the factory. There, in my own factory, I could add posibility to listen to created lock nodes and apply GC/heartbeat logic. As you suggested, same could be done if node creation would be moved to the LockInternalsDriver and made public/reusable. I like this even better. It could be tricky how to reuse e.g. read-write lock, but it would not be so painful to "re-implement" only that part of curator code on my end. Jozo On Tue, Jan 14, 2014 at 6:51 PM, Jordan Zimmerman < [email protected]> wrote: > You might be able to re-use the code in the LockInternals class. It could > easily be modified to do what you want via the LockInternalsDriver. Of > course it would need to be made public. The gc/heartbeat stuff would have > to be coded fresh, though. > > -Jordan > > ------------------------------ > From: Jozef Vilcek Jozef Vilcek <[email protected]> > Reply: Jozef Vilcek [email protected] > Date: January 14, 2014 at 12:18:15 AM > To: Jordan Zimmerman [email protected] > Subject: Re: Persistent locks > > Yes, you are correct. I tried to sketch this in my post. There will be > possibility to create persistent lock, which will cause deadlock if holder > crashes and one with possibility to to be gc collected after some time if > holder crashes. The mechanism for this has to be implemented. > > Off course that I use "classical" ephemeral locks where possible. But I > have few cases where it is not feasible. > > > On Tue, Jan 14, 2014 at 2:42 AM, Jordan Zimmerman < > [email protected]> wrote: > >> How will you avoid dead locks? You’ll need to write some kind of >> heartbeat/gc mechanism to the lock. Otherwise I don’t see how it works if >> the lock holder crashes. >> >> -JZ >> >> ------------------------------ >> From: Jozef Vilcek Jozef Vilcek <[email protected]> >> Reply: [email protected] [email protected] >> Date: January 13, 2014 at 7:24:06 AM >> To: [email protected] [email protected] >> Subject: Persistent locks >> >> Hi >> >> I have a question about curator locks. I see that locks are implemented >> via znode type EPHEMERAL_SEQUENTIAL. I am thinking about having an >> implementation via PERSISTENT_SEQUENTIAL. >> >> Main reason for this are processes with critical sections, where we can >> not afford to loose a lock due to session expiration. In such case, others >> might acquire a lock and kick in while the previous process is still >> running but e.g. experiencing connection issues. To kill this temporally >> detached process in favor of others would be too costly. >> >> My thoughts are to have: >> >> * Persistent lock - if something go south and client code does not >> release lock, it will stay there until removed by manual or some other >> intervention >> >> * Persistent ephemeral lock - this would be ephemeral implemented by >> persistent lock. For not so much critical stuff but e.g. for unstable >> environments. This would install kind of refresh hook on a created lock >> node. Other clients waiting to acquire lock could garbage collect locks >> which does not received refresh for reasonable long time (scaling beyond >> session timeouts). >> >> What I would like to know: >> >> * any wisdom, if this does make sense or if there is a better way out >> there >> * support from curator ... There is a lot of good code in curator I would >> have to copy to make this work. I want to avoid this. Would it be possible >> of provide either path for making locks core extensible/reusable (or to >> contribute implementation of locks if considered worth for framework) ? >> >> >> Best, >> Jozo >> >> >
