K 10
svn:author
V 6
jilles
K 8
svn:date
V 27
2013-05-12T16:11:23.388571Z
K 7
svn:log
V 933
MFC r249566,r249644: EINTR in POSIX sem_*.

Document that sem_wait() can fail with [EINTR].

Programs often do not expect an [EINTR] return from sem_wait() and POSIX
only allows it if the signal was installed without SA_RESTART. The timeout
in sem_timedwait() is absolute so it can be restarted normally.

The old POSIX semaphore implementation did this correctly, unlike the new
umtx one.

Specific to 9-stable: UMTX_ABSTIME does not exist and therefore
sem_timedwait() is erroneously not restarted after a SA_RESTART signal
handler.

It may be desirable to avoid [EINTR] completely, which matches the pthread
functions and is explicitly permitted by POSIX. However, the kernel must
return [EINTR] at least for signals with SA_RESTART clear, otherwise pthread
cancellation will not abort a semaphore wait. In this commit, only restore
the 8.x behaviour which is also permitted by POSIX, as far as possible with
the ABI in 9-stable.

END