Re: [libvirt] [PATCH 1/3] virthread: Introduce virRWLockInitPreferWriter
On Mon, Jul 24, 2017 at 01:12:59PM -0400, John Ferlan wrote:
On 07/19/2017 10:31 AM, Michal Privoznik wrote:
> We already have virRWLockInit. But this uses pthread defaults
> which prefer reader to initialize the RW lock. This may lead to
> writer starvation. Therefore we need to have the counterpart that
> prefers writers. Now, according to the
> pthread_rwlockattr_setkind_np() man page setting
> PTHREAD_RWLOCK_PREFER_WRITER_NP attribute is no-op. Therefore we
> need to use PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
> attribute. So much for good enum value names.
>
> Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
> ---
> src/libvirt_private.syms | 1 +
> src/util/virthread.c | 35 +++++++++++++++++++++++++++++++++++
> src/util/virthread.h | 1 +
> 3 files changed, 37 insertions(+)
>
This has broken the CI build, freebsd is not happy:
../../src/util/virthread.c:133:42: error: use of undeclared identifier
'PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP'
pthread_rwlockattr_setkind_np(&attr,
PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
^
1 error generated.
It is not just FreeBSD, it also breaks OS-X and Win32.
The suffix '_np' / '_NP' is shorthand for nNon portable" - these
are glibc inventions. IMHO we should not really use this in our
code as if we're going to make assumptions that writers are not
starved as a result, because writers will be starved on any
non-Linux platform.
IOW, I think we need to just revert this.
Regards,
Daniel
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