Re: squid-smp: synchronization issue & solutions

On Mon, 2009-11-16 at 00:29 +0530, Sachin Malave wrote:
> Hello,
>
> Since last few days i am analyzing squid code for smp support, I found
> one big issue regarding debugs() function, It is very hard get rid of
> this issue as it is appearing at almost everywhere in the code. So for
> testing purpose i have disable the debug option in squid.conf as
> follows
>
> -------------------------------
> debug_options 0,0
> -------------------------------
>
> Well this was only way, as did not want to spend time on this issue.....

Its very important that debugs works.

> 1. hash_link ---- LOCKED

Bad idea, not all hashes will be cross-thread, so making the primitive
lock incurs massive overhead for all threads.

> 2. dlink_list ---- LOCKED

Ditto.

> 3. ipcache, fqdncache ---- LOCKED,

Probably important.

> 4. FD / fde handling ---WELL, SEEMS NOT CREATING PROBLEM, If any then
> please discuss.

!!!! we need analysis and proof, not 'seems to work'.

> 5. statistic counters --- NOT LOCKED ( I know this is very important,
> But these are scattered all around squid code, Write now they may be
> holding wrong values)

Will need to be fixed.

> 6. memory manager --- DID NOT FOLLOW

Will need attention, e.g. per thread allocators.

> 7. configuration objects --- DID NOT FOLLOW

ACL's are not threadsafe.

> AND FINALLY, Two sections in EventLoop.cc are separated and executed
> in two threads simultaneously
> as follows (#pragma lines added in existing code, no other changes)

I'm not at all sure that splitting the event loop like that is sensible.

Better to have the dispatcher dispatch to threads.

-Rob