Open Radar

 
Summary:
The read() system call does not appear to be restarted when interrupted by SIGTTIN.  Instead, read() returns EINTR, which many programs do not expect.

Steps to Reproduce:
This is trivially repeatable with cat(1) by putting it in the background, and then foregrounding the process.

Expected Results:
Other operating systems restart the read(), and cat resumes, like so:

bash-3.2$ cat &
[1] 13082
bash-3.2$ fg
cat

Actual Results:
bash-3.2$ cat &
[1] 46363
bash-3.2$ %1
cat
cat: stdin: Interrupted system call
bash-3.2$

Regression:

Notes:
This is not a bug in cat.

It's worth noting that this happens regardless of whether SA_RESTART is set.

Fom a quick scan of the xnu tty code the problem may simply be that ttread(), ttywrite() and ttioctl() return EINTR instead of ERESTART.  Other BSD tty implementations use ttysleep() in these locations.