Concurrent::Promise causing error with Rails.cache/.fetch

[cwli24]

    #Make a HTTP GET promise for each tag (execute inline).
    (0...tags.size).each do |idx|
      fetch_requests[idx] = Concurrent::Promise.execute do
        # We'll read from the cache first to see if the data already lives there.
        response = Rails.cache.fetch( tags[idx], expires_in: 3.hours, race_condition_ttl: 2) do
          HTTP.get(EXTDATA_URL, :params => {:tag => tags[idx]})
        end
         ...
     Concurrent::Promise.all?(*fetch_requests).execute.wait!

This is causing the same crash from the server. I tried using :file_store as cache rather than :memory_store (which was made 'thread-safe' by Rails anyways), and also using ReentrantReadWrite lock to gate the cache, but no success. This is what's showing:

* Operating system:                linux
* Ruby implementation:             Ruby
* `concurrent-ruby` version:       1.1.10
* `concurrent-ruby-ext` installed: yes
* `concurrent-ruby-edge` used:     no

[cwli24]

Actually this may be(?) related to an issue with the cache; just the trace has a poor way of showing it. I tried using the native Thread class via replacing Promise.execute with Thread.new and fetch_requests.each(&:join), and it's also failing on the fetch return, saving data to the cache. I'm suspicious the cache might just not like storing http responses..

[cwli24]

I'm fairly certain the root of this is actually caused by what's being stored into the cache, and subsequently this problem. I'm going to close this issue, and link the one I opened on Rails' github.