In trunk (r37474), there is a typo in a macro name in the rb_reserved_fd_p() function. This prevents any actual checking that the file descriptor is reserved by the VM.
This issue was solved with changeset r37483.
Mark, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
thread_pthread.c (rb_reserved_fd_p): fix typo in macro check
that prevented the ifdef ever being true.
[Bug #7281] [ruby-core:48940]