Single backround thread in with multiple workers

nginx.conf

error_log  logs/error.log debug;
events {
    worker_connections  1024;
}

worker_processes 4;

http {
    default_type  application/octet-stream;

    lua_shared_dict test_dict 1m;

    init_by_lua '
        function my_bg_func(premature)
            -- Set timer immediately so it will always run on the 10s mark
            local ok, err = ngx.timer.at(10, my_bg_func)
            if not ok then
                ngx.log(ngx.ERR, "Failed to start background thread: "..err)
            end

            local dict = ngx.shared["test_dict"]
            local lock, err = dict:add("flag", ngx.worker.pid(), 30)

            if lock then
                ngx.log(ngx.DEBUG, ngx.worker.pid(), " locked")

                ngx.sleep(2) -- Simulate doing some work

                local pid, err = dict:get("flag")
                if pid == ngx.worker.pid() then
                    dict:delete("flag")
                else
                    ngx.log(ngx.DEBUG, "couldnt release lock")
                end
            else
                if err == "exists" then
                    return
                else
                    ngx.log(ngx.ERR, err)
                end
            end
        end
    ';

    init_worker_by_lua '
        local dict = ngx.shared["test_dict"]

        local ok, err = ngx.timer.at(1, my_bg_func)
        if not ok then
            ngx.log(ngx.ERR, "Failed to start background thread: "..err)
        end
    ';

}