[ruby-core:102676] [Ruby master Bug#17664] Behavior of sockets changed in Ruby 3.0 to non-blocking

Issue #17664 has been updated by jeremyevans0 (Jeremy Evans).

Assignee set to ioquatix (Samuel Williams)
Status changed from Open to Assigned

I believe this is expected, even if not mentioned in the release notes.  I think the Ruby-level API remains the same, but passing the underlying file descriptors to C functions can see changed behavior.  Assigning to @ioquatix to confirm this is expected.

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Bug #17664: Behavior of sockets changed in Ruby 3.0 to non-blocking
https://bugs.ruby-lang.org/issues/17664#change-90670

* 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
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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/ext/socket/init.c#L411-L434). 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/d3c9cf3ddc1f414387948fa40e5f6a24f68bf045/ext/polyphony/backend_io_uring.c#L28-L47) is to make sure `O_NONBLOCK` is not set before attempting I/O operations on any fd.



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