Issue #17664 has been updated by ioquatix (Samuel Williams). Regarding `IO.select`, my advice is to prefer `wait_readable` or `wait_writable` if possible. ---------------------------------------- Bug #17664: Behavior of sockets changed in Ruby 3.0 to non-blocking https://bugs.ruby-lang.org/issues/17664#change-101590 * Author: ciconia (Sharon Rosner) * Status: Assigned * Priority: Normal * Assignee: ioquatix (Samuel Williams) * ruby -v: 3.0.0 * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN ---------------------------------------- I'm not sure this is a bug, but apparently a change was introduced in Ruby 3.0 that makes sockets non-blocking by default. This change was apparently introduced as part of the work on the [FiberScheduler interface](https://github.com/ruby/ruby/blame/78f188524f551c97b1a7a44ae13514729f1a21c7/...). This change of behaviour is not discussed in the Ruby 3.0.0 release notes. This change complicates the implementation of an io_uring-based fiber scheduler, since io_uring SQE's on fd's with `O_NONBLOCK` can return `EAGAIN` just like normal syscalls. Using io_uring with non-blocking fd's defeats the whole purpose of using io_uring in the first place. A workaround I have put in place in the Polyphony [io_uring backend](https://github.com/digital-fabric/polyphony/blob/d3c9cf3ddc1f414387948fa40e5...) is to make sure `O_NONBLOCK` is not set before attempting I/O operations on any fd. -- https://bugs.ruby-lang.org/