A series of commands is not atomic. If you issue a 'get' against an item, operate on the data, then wish to 'set' it back into memcached, you are not guaranteed to be the only process working on that value. In parallel, you could end up overwriting a value set by something else. [...] But PECL Memcached come with a useful function : cas().

The "cas()" function uses a checksum pulled out when the data is uplled using "get()". This token along with the updated data is passed into the "cas()" method that does the additional checking for you. A code snippet is included to show you its use.

The idea behind the new extension is to leverage the functionality contained libmemcached - a solution which has been widely adopted across many scripting communities and beyond. The extension is available in PECL and has lots of shiny new functionality. This article looks at how to obtain and work with the new extension, and also shows off a couple of the new features it includes.

Lorna talks a bit about the features of the extension in general but mentions two great new ones specifically - the "getmulti" fetch method allows for grabbing multiple chunks of cached information and the cas (compare and swap) function that works the same as a replace but checks the current contents first.