Which ruby methods free GVL?

In multi-threaded ruby execution, you cannot get parallel execution of threads unless you use those functions which frees GVL.

In my understanding, following ruby methods frees GVL:

• Kernel#sleep
• IO#read and IO#write

Question

• In pure ruby, is there any other methods which frees GVL?

Version

• I'm currently using ruby version 2.6, so expect the info of this version.

I asked same question on stackoverflow (Japanese).

Got this answer https://ja.stackoverflow.com/a/55579/754 , which stating that

• Bignum's div / modulo
• Dir.new/Dir.open
• Dir.chdir
• Dir.rmdir
• Dir.empty?
• Dir.glob
• File.chown
• File's methods which check file status, namely stats
• File.rename
• File.truncate
• File.mkfifo
• IO.copy_stream
• IO.#open and IO.#close related codes (was too complex to understand)
• Kernel.#system
• Kernel.#exec

and in other standard libraries such as fiddle, openssl, readline, socket, zlib actually calls method which frees GVL.

this great answer was written by https://stackoverflow.com/users/4944814/raccy