Confusion with Thread Safety in Ruby 3.1 while Using Redis for Caching
I'm converting an old project and This might be a silly question, but I'm facing an issue with thread safety in Ruby 3.1 when using Redis to store cached data in a multi-threaded environment. I'm using the Redis gem (version 4.2.5) and the following code snippet to cache some data: ```ruby require 'redis' require 'thread' class CacheManager def initialize @redis = Redis.new end def fetch_data(key) @redis.get(key) || cache_data(key) end def cache_data(key) data = expensive_operation(key) @redis.set(key, data) data end def expensive_operation(key) # Simulate an expensive operation sleep(2) "Data for #{key}" end end ``` I'm using this `CacheManager` class in a threaded environment: ```ruby manager = CacheManager.new threads = [] 10.times do |i| threads << Thread.new do puts manager.fetch_data("item_#{i}") end end threads.each(&:join) ``` However, I've been noticing that sometimes, multiple threads fetch the same data, leading to duplicated calls to `expensive_operation`, resulting in unexpected delays. I expected the data to be cached after the first call, but it seems that the cache is not being accessed properly. I checked the Redis logs and confirmed that the data is being set correctly, yet the `fetch_data` method is called multiple times for the same key. To mitigate this, I tried using a mutex to synchronize access: ```ruby class CacheManager def initialize @redis = Redis.new @mutex = Mutex.new end def fetch_data(key) @mutex.synchronize do @redis.get(key) || cache_data(key) end end # rest of the class... end ``` But this approach seems to block threads unnecessarily, which isn't ideal for performance. Is there a better way to handle caching in a multi-threaded context without significant delays? Any insights on ensuring thread safety in this scenario would be greatly appreciated! What's the best practice here? Am I missing something obvious? I'm developing on Windows 11 with Ruby.