preserve errno when inside sig handler for self-pipe

We must not clobber errno of the main thread inside signal
handler in case write fails.

This bug only affects systems without epoll_pwait where the
self-pipe is required, so it does not affect modern GNU/Linux
systems; but does affect FreeBSD systems and anybody else
relying on kqueue.

Thanks to Steven Stewart-Gallus for a Ruby bug report which
inspired this fix: https://bugs.ruby-lang.org/issues/10866

Cc: Mykola Golub <trociny@FreeBSD.org>
Cc: Steven Stewart-Gallus <sstewartgallus00@mylangara.bc.ca>

0 files changed, 0 insertions, 0 deletions