12 Jul
2011
12 Jul
'11
7:25 a.m.
from my understanding, sem_post() implies a write
barrier (stores have been
executed before sem_post()) and sem_wait() a read barrier (loads have to be
executed after sem_wait()).
Given that a mutex can be replaced with a semaphore initialized with 1
(then lock == sem_wait, unlock == sem_post), your statement should be
true as long as the semaphore value is 0 / 1.
However, I don't know if your statement must still be true when the
semaphore is used as a count tied to a number of items, i.e. when it
always hovers above 1. POSIX talks about a "thread of control", but in
this case, there is no exclusion, thus no "thread of control".
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag…
(same link as a few posts ago)
-- Dan