This is likely what was done. Nobody really cares if a hit counter on a web page loses a few updates.

For a view counter - yes, you can use a full blown database to concurrently increment a simple integer value; or, you could do it in a few lines of code by yourself too.

Overkill, If you are writing to the text file only to increment a number of visitors, none of what you mentioned above is even required.

Create a "counter-hit" file for each visitor, count the number of files in the resources directory. Populate the master file with the file count and delete all the temporary files. Configure it on a crontab for say every three seconds.

Online now was even easier. IFrame refresh within the homepage. Upon refresh, populate the file with something like "online=true". Read the file every X, if the file modifcation hasn't been refreshed within 30 seconds, nerf the text file and mark that user as offline. psuedo-dynamic, but times were different then. I coded these in perl back in the day for my RTCW clan and how I miss it much.

Being a webmaster was art, an art that's now lost..

Of course you have to make sure to not run out of diskspace or max file size of the OS/filesystem (2GB on a 32bit system?)

https://www.php.net/manual/en/function.flock.php

Or redis.