ruby - Rails with mutex on class variable, rake task and cron -

sorry such big question. not have experience rails threads , mutex.

i have class follow used different controllers license each customers.

customers , licenses gets added , removed every hour. api available customers , licenses.

i plan create rake task call update_set_customers_licenses, run hourly via cronjob.

i have following questions:

1) mutex, there potential problem, there chance rake task can occur while updating. idea on how solve this?

2) design below writes json out file, done safety api not reliable. can seen, not reading file back, in essence file write useless. tried implement file read mutex , rake task, gets confusing. pointers here.

class customer   @@customers_to_licenses_hash = nil   @@last_updated_at = nil   @@mutex = mutex.new    customers_licenses_file = "#{rails.root}/tmp/customers_licenses"    def self.cached_license_with_customer(customer)     rails.cache.fetch('customer') {self.license_with_customer(customer)}   end    def self.license_with_customer(customer)     @@mutex.synchronize       license = @@customers_to_licenses_hash[customer]       if license         return license       elsif(@@customers_to_licenses_hash.nil? || time.now.utc - @@last_updated_at > 1.hours)         updated = self.update_set_customers_licenses         return @@customers_to_licenses_hash[customer] if updated       else         return nil       end     end   end    def self.update_set_customers_licenses     updated = nil     file_write = file.open(customers_licenses_file, 'w')     results = self.get_active_customers_licenses     if results       @@customers_to_licenses_hash = results       file_write.print(results.to_json)       @@last_updated_at = time.now.utc       updated = true     end     file_write.close     updated   end    def self.get_active_customers_licenses     #http thru api     #return hash of records   end end 

i'm pretty it's case every time rails loads, environment "fresh" , has no concept of "state" in between instances. say, mutex in 1 ruby instance (the 1 request rails) has no effect on second ruby instance (another request rails or in case, rake task).

if follow data upstream, you'll find common root of every instance can used synchronize them database. use transactional blocks or maybe manual flag set , unset in database.