Ruby Concurrency

GIL

https://yehudakatz.com/2010/08/14/threads-in-ruby-enough-already/

• Can’t run Ruby code in the same process in multiple threads at the same time
• But when a thread blocks on I/O, another thread can run
• For example, you can run multiple HTTP requests in parallel, or multiple database queries in parallel
• You do need one Ruby process per CPU core. But with multithreading you should not need more than one.

Processes

• You can run separate Ruby processes which can run in parallel
• Web servers like Puma allow multiple processes

Threads

• Web servers like Puma allow multiple threads
• Rails has been thread-safe since 2.2

Fibers

• Added in Ruby 1.9
• A coroutine mechanism
• Fiber.new, yield, resume

Async Fibers/Scheduler

• For I/O heavy tasks
• Like Async/Await in JS
• Can’t use multi-core
• https://github.com/socketry/falcon
• https://www.youtube.com/watch?v=Y29SSOS4UOc

Ractor (previously known as guilds)

• For multi-core
• For CPU-intensive tasks
• Isolated object space. Nothing mutable shared. Immutable things can be shared
• Interpreter lock will now be per Ractor, for threads within the Ractor
• https://www.youtube.com/watch?v=0kM7yFM6Dao&list=PLbHJudTY1K0cyDs1ZwFLzlfQqvkDKt17N&index=12