I can't really comment on your code (don't use threads but preforking in my code, haven't done threads for years), just let me say this:

While there are some minor indentation problems in your code, i find the code layout and the comprehensive information provided by you most enjoyable. Thank you for caring :-)

As i said, i use forking/preforking in my bigger projects. For interprocess communication i use two systems in combination: When race conditions don't really matter (either because only one process writes the data or because the data integrity isn't that important), i use memcache because it's quite fast.

When data integrity really matters and speed has a lower priority than integrity, i generally use a database. ACID compliant databases are a modern marvel when it comes to data integrity.

It of course all depends what your final goal is and what your application is trying to achieve if you can go one of these routes (or a combination thereof).

BREW /very/strong/coffee HTTP/1.1
Host: goodmorning.example.com

418 I'm a teapot