Re: [naviserver-devel] read/write ns_config

[Zoran V. <zv...@ar...>]

On 22.08.2006, at 22:13, Stephen Deasey wrote:

>
> I don't see how you will handle the locking...  :-(

If you go and get the:

https://sourceforge.net/tracker/? 
func=detail&atid=719009&aid=1549952&group_id=130646

you can inspect the code ans see how I'm doing the locking.

Essentially (in a nutshell) every thread has its own
private copy of all config parameters it requested so far.
There is also a shared configuration, holding ALL known
config parameters.

Under normal circumstances, a reader will go to the shared
config for a parameter only once: first time it fetches the
param. All other accesses to the same param are done in
the local (per-thread) cache. The cache is locked in order
to synchtonize with the writer thread.

A writer thread will update the shared config and then walk
private configs of all theads (which registered themselves
for a given section - see above) and update them one by one,
locking each as it goes.

Since I expect writers to be *far* less active, the reader
will almost always succeed in locking the private cache.
Hence, almost no locking contention!

A bad scenario can happen if you have numerous threads
reading the same parameter at the same time. Then
you will get contention on the shared config mutex. But
this is normally not going to happen in real life, and if
it happens it will be a very short interval as after that
all will be cached per-thread privately.

I believe this is pretty good. It uses some more memory
but avoids locking contention at maximum.

What do you think?

Cheers
Zoran