1
You can create a lock by using flock on one of your existing files (or create a special one fo this. Get the lock before you start the canculation and release it after the result was stored.
1
I found the function to achieve the goal - get_blog_option($blogId, $optionKey)
https://codex.wordpress.org/WPMU_Functions/get_blog_option
1
I solved the issue thanks to this answer: Serialized settings in rest api.
I was able to store all the options as a json object:
/**
* Create plugin options schema as an object and prepare it for the rest api.
* WP >=5.3
*/
function my_register_settings() {
$general_options = [
'show_in_rest' => [
'schema' => [
...
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