What is a good method to retain a small piece of data across multiple calls of a PHP script, in such a way that any call of the script can access and modify its value - no matter who calls the script?
I mean something similar to $_SESSION variable, except session is strictly per-client; one client can't access another client's session. This one would be the same, no matter who accesses it.
Losing the value or having it corrupted (e.g. through race conditions of two scripts launched at once) is not a big problem - if it reads correctly 90% of the time it's satisfactory. OTOH, while I know I could just use a simple file on disk, I'd still prefer a RAM-based solution, not just for speed, but this running from not very wear-proof flash, endless writes would be bad.
Take a look at shared memory functions. There are two libraries that can be used to access shared memory:
For storing binary data or one huge String, the Shared Memory library is better, whereas the Semahpores library provides convenient functions to store multiple variables of different types (at the cost of some overhead, that can be quite significant especially for a lot of small-sized (boolean for example) variables.
If that is too complex, and/or you don't worry about performance, you could just store the data in files (after all, PHPs internal session management uses files, too....)
A good alternative to using a database would be memcache!
来源：https://stackoverflow.com/questions/21947595/php-session-like-storage-global-across-all-users