Sharing changable data inside a worker and timers

I have read this part of the documentation https://github.com/openresty/lua-nginx-module#data-sharing-within-an-nginx-worker

Which is what I need, but I also require that a variable inside a module I define, is accessed within the worker (request handlers). But it is updated through a timer.every mechanism so something like this.

init_worker_by_lua_block : Create timer to update the variable.
server_rewrite_by_lua_block: Use the variable. (I chose server_rewrite because I thought it is earlier stage than rewrite)

The variable is an integer, so I am asking if this usage is subject to race condition. It's an integer, so I could easily make it an atomic operation to set/get it in C (without locks). But that means writing an Nginx module. I was wondering if this was also possible with Lua.

Edit: Maybe a clever trick like employing https://www.lua.org/manual/2.1/subsection3_5_2.html (I have no experience with it), to retain/implement the atomic ability of setting and reading an integer in C.

Edit_2: Would making the variable not global (_M), but accessed through getter/setter functions in the module, but kept in the lua module as local var = 3; help? Like helping with concurrency and avoiding table look up.

Read the linked data-sharing documentation and the init_worker_by_lua_block and server_rewrite_by_lua_block entry points first. Determine whether timer updates and request-handler reads are supported, including the proposed local getter/setter approach; done would be a documented, project-backed answer or clarified guidance.