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NetBSD vs Solaris condvar semantics
I'm working on fixing ZFS locking, and I ran into a diference between
NetBSD's and Solaris's interpretation of condvars.
In Solaris, it seems to be kosher to do
at least if waiters use only cv_wait and not cv_wait_sig &c. That
idiom makes NetBSD very unhappy, though, because cv_wait wants to
continue using cv after it is woken, at which point cv may already be
ZFS makes nontrivial use of this idiom, such as in dirent locks and
range locks. One way to work around this is to do reference counting
for the condvars; that is, to change
and to change
so if there are any waiters, we just let the last waiter destroy it.
This is what I started to do for dirent locks, until I saw that there
are more uses of the idiom, and I don't know how many others I'll come
Alternatively, we could instead allow this idiom, and leave the ZFS
use of it as is, with a minor change to cv_wait in kern_condvar.c,
since it doesn't actually need cv for anything after waking. (The
change to rump would be a trifle less minor.)
How tasteless would it be to change cv_wait to allow this idiom?
Should I just continue converting it to reference counts?
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