[asterisk-dev] [Code Review] Implement ast_channel_search_locked to expensive per-notify channel walk in chan_sip

Steve Murphy murf at digium.com
Thu Nov 6 11:40:30 CST 2008

On Wed, 2008-11-05 at 10:44 +0000, Tim Panton wrote:
> On 4 Nov 2008, at 23:54, Brian Degenhardt wrote:
> >
> > That's what I was thinking, but I was wondering if Murf and Russell
> > could comment on if that approach is adequate, or if we want to  
> > maintain
> > a hashtab of channels keyed on linkedid, and insert/remove them from  
> > there.
> >
> > I'm sorta partial to your way, above.  While it's slower, we don't  
> > have
> > to worry about maintaining the separate data structure which has the
> > potential to get out of sync.  Especially since this code only runs if
> > you care about LINKEDID_END events.
> I've been so long out of the C world I'm not sure this helps, but we
> had a similar problem _years_ ago and I ended up solving it with a weird
> dual purpose data structure. It was (originally) a linked list the  
> sequence
> mattered and in some cases it needed to be walked in order.
> The most frequent access was a name based lookup that was independent
> of sequence for which we really wanted a hashtable.
> What we did was to replace the 'malloc/free' code in the linked list  
> insert/delete.
> It allocated a slot in a hash table (based on a hash of the name). All  
> the
> list walk stuff worked exactly as before, but we added a fast  
> find_by_name()
> that used the hashtable. It gave us a huge speedup. The only problem  
> was when
> the names changed. - we had to implement that as a delete/add.
> Tim.


Using multiple structures to provide different access methods to the
set of items is definitely an option. As usual, there are speed/size 
compromises to make, where size is both code and memory.


Steve Murphy
Software Developer
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