How is modular access serialized in Perl?

[craigt]

Several years back, I built a dll of database functions in C with another person. We serialized access to ensure that only 1 client at a time was in any function.

Imagine for example, a Perl application where multiple clients are using a UI to enter the same type of data.
When the data is saved by the clients, its posted to the same backend code that puts it in a file. Some of these clients may save at the 'same' time.

Please explain how this works as a client/server process in Perl. Please answer like I'm a beginner or point me to a good online explanation.

Thanks

[craigt]

I think the answer is in the session idea as implemented in Perl and the consistent use of Perl voluntary locking.