Re: [naviserver-devel] Excessive locking in urlspace?

[Vlad S. <vl...@cr...>]

I think ns_register_proc/ns_register_filter uses Trie and canbe called 
at any time, that's why it still needs locking.

Double locking should be avoided but i would keep the ability to call 
ns_registerXXX procs at any time.

Stephen Deasey wrote:
> Ns_ConnRunRequest in op.c does something like:
> 
> Ns_MutexLock(&ulock);
> reqPtr = Ns_UrlSpecificGet(server, method, url, id);
> ...
> Ns_MutexUnlock(&ulock);
> 
> 
> Ns_UrlSpecificGet in urlspace.c does something like:
> 
> MkSeq(&seq, server, method, url);
> Ns_MutexLock(&lock);
> data = JunctionFind(&urlspace, seq, id, 0);
> Ns_MutexUnlock(&lock);
> 
> 
> i.e. there's double locking going on.  The second lock, in the
> urlspace code, is under contention by all callers of urlspace
> (requests, url2file, etc.), and many of these are very common
> operations.
> 
> 
> Users of urlspace need to call Ns_UrlSpecificAlloc() in their
> initialisation code to get a magic ID.  This ID partitions the data of
> each subsystem.  But the ID is stored within the 'Trie' and so needs
> to be protected by the global lock.
> 
> What if instead the ID was used as in Thread Local Storage?  There's
> an array of slots, where each slot contains a separate Trie, and the
> ID is an index into this array.  Because ID's are allocated at start
> up and aren't destroyed there need be no locking at run time to locate
> the appropriate Trie for the caller.
> 
> The urlspace locking can now be removed because the callers locking
> perfectly protects the Trie from concurrent access.  It would also
> allow the caller to run lock-free in the case where all urlspace
> entries are created at start up and only read at run time.
> 
> 
> Does this make sense?
> 
> 
> -------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
> for problems?  Stop!  Download the new AJAX search engine that makes
> searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
> http://ads.osdn.com/?ad_idv37&alloc_id865&op=click
> _______________________________________________
> naviserver-devel mailing list
> nav...@li...
> https://lists.sourceforge.net/lists/listinfo/naviserver-devel
> 

-- 
Vlad Seryakov
571 262-8608 office
vl...@cr...
http://www.crystalballinc.com/vlad/