[jira] [Commented] (CURATOR-28) Add Expiry Time To InterProcessLocks

["3l3ph4n1n3 (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CURATOR-28?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13675528#comment-13675528 ] 

3l3ph4n1n3 commented on CURATOR-28:
-----------------------------------

It's indeed cautious - but I really don't want my distributed locks to have a single point of failure (as you can't guarantee clients don't have bugs).

Some more examples here - https://en.wikipedia.org/wiki/Lease_%28computer_science%29#Motivation - and I've seen a client throw NoClassDefFoundErrors at runtime as one of the jars on its classpath was temporarily unreachable as it was on a networked file system!

If I submitted a patch that (optionally) made all the clients attempt to delete a lock node after a fixed (but configurable) amount of time, would you consider including it? It'd remove the single point of failure (as any client can release the lock after the timeout, not just the one that took it), and this kind of functionality would ideally be part of the library anyway (to prevent applications that need it from writing pretty much the same code every time).
                
> Add Expiry Time To InterProcessLocks
> ------------------------------------
>
>                 Key: CURATOR-28
>                 URL: https://issues.apache.org/jira/browse/CURATOR-28
>             Project: Apache Curator
>          Issue Type: New Feature
>          Components: Recipes
>    Affects Versions: 2.0.0-incubating
>            Reporter: 3l3ph4n1n3
>            Priority: Minor
>
> If a client takes a distributed lock and fails without breaking its zookeeper connection (e.g. the main application thread deadlocks) then that lock will never be released (at least without manual intervention, e.g. killing the process that has it). When a client's acquiring a lock I'd like to be able to specify a time after which the lock is automatically released. If the client currently holds the lock it should be able to extend this time period as many times as it likes. A write-up for what I'm describing for redis is here: https://chris-lamb.co.uk/posts/distributing-locking-python-and-redis .
> I can see a couple of ways of going about this - the lock lifetime could be stored in the node's date (and so clients could check if the node had expired by adding the lifetime to the node's ctime or mtime). However, comparing the client's current time with the expiry time in the node is probably not the right thing to do as the client's clock may be out of sync with the other clients (or the zookeeper nodes). It'd be nice if zookeeper could automatically delete nodes (i.e. release the lock) after a certain amount of time - i.e. make it the zookeeper cluster's decision when the lock is expired, not the client's decision. However, I'm not sure exactly how to do this...
> Thanks,

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira