Good morning everyone

I'm having a some problems with jRuby (9.2.11.1) and using multiple threads, I don't know if this is the right place to ask for help, if not please just let me know where I can do it.

I have an api using roda and jruby, it gets multiple jsons in a request, parses them, does a few changes and then writes every json to disc using lib::gzipWriter.
The api is running inside a tomcat container and I have been doing a multiple tests forcing tomcat to use a fixed number of threads and using 50.000 jsons divided in requests with 250 each.

Here are the results I got form beginning to end of execution.
1 thread  - 21 minutes
3 threads - 19 minutes
10 threads - 19 minutes 

I logged the thread ids and I can see multiple threads running but the results don’t seem to reflect that. Can anyone help me understand what I should do?