What do you mean by "atomic" ?
The add operation itself is "atomic", ie:
$mc->add('user1lock', 10);
... will bail if the key already exists, or return true if it did not exist.
However:
$mc->add('user1lock', 10);
$mc->set('blah blah blah');
... does _not_ *absolutely* guarantee the lock still exists by the time
set gets called. 99.9995% of the time it'll still be in cache, but
there's a small chance it could get ejected, which gets wider when
there's more time between the add call and the set call, and depending
on other factors.
So we can't say it's atomic, it's more like a ghetto lock that usually
works. You can use it for situations where you want to reduce the number
of processes running something in parallel, but you can't use it if you
need to _guarantee_ they won't run it in parallel.
-Dormando
Fausto Richetti Blanco wrote:
Hello,
I’ve found this entry on the FAQ:
“One should be mindful about possible issues in populating or
repopulating our cache. Remember that the process of checking memcached,
fetching SQL, and storing into memcached, is **not** atomic at all!”
I know it’s talking about the entire process, but I want to
confirm with you whether the add function is atomic or not. I want to
use memcache to simulate locking and this atomicity is very important to
the whole process.
Thanks in advance,
**Fausto Richetti Blanco**
**CWI Software - CMMI Nível 2**
Desenvolvimento
//(51) 3264-3737//
http://www.cwi.com.br <http://www.cwi.com.br/>
