How can I synchronize two processes accessing a file on a NAS?

Question

Here's the thing: I have two applications, written in C++ and running on two machines with different OS (one Linux and one Windows). One of this process is in charge of updating an XML file on a NAS (Network Attached Storage) while the other one reads this file.

Is it possible to synchronize these two processes in order to avoid reading of the file at the same time it's being modified?

Answer 1

You could create a lock file on the server that is created before you do a write, wait then write and delete on completion., Have the read process check for the token before reading the file.

Edit: To address the comments, you can implement a double-checked locking type pattern. Have both reader and writer have a locking file and double check before you do work, something like:

Reader: Check for write lock file, create read lock file, check for write lock file, if exists delete read file and abort.

Writer: Check for read lock file, create write lock file, check for read lock file, if exists delete write lock file and abort.

This will stop your processes trampling on each other but a potential race condition may occur in that the you could potentially have both processes check, create then recheck simultaneously though this will not cause the data to be read in an inconsistent state but will cause both read and write processes to abort for your specified delay