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Re: [PATCH][BZ #15790] Have pthread_mutexattr_gettype mask out the elision bit.

On Mon, Nov 11, 2013 at 08:06:20AM -0800, Cesar Philippidis wrote:
> On 11/7/13, 8:17 PM, Rich Felker wrote:
> > On Thu, Nov 07, 2013 at 06:57:15PM +0100, Andi Kleen wrote:
> >>> Andi, it is unclear that if this is desired behaviour, one argument
> >>> againist could be that if user wants to clone mutex type like
> >>>
> >>> int tp;
> >>> pthread_mutexattr_gettype(a1, &tp);
> >>> pthread_mutexattr_settype(a2, tp);
> >>>
> >>> should it preserve elision or not?
> >>
> >> Yes it should.
> > 
> > Sorry, it can't. The interface contact is set by POSIX, not something
> > for glibc to design.
> I'm confused. Is it OK for pthread_mutexattr_gettype() mask out the non
> portable elision bits, PTHREAD_MUTEX_NO_ELISION_NP and
> PTHREAD_MUTEX_ELISON_NP, set by pthread_mutexattr_settype()?

Your question is misleading. As far as I understand,
pthread_mutexattr_settype does not, from an application perspective,
"set the elision bits of type". It sets the type, which might, due to
the semantic requirements of the type, require forcing elision off, or
allow a default of elision-on to be applied. As an implementation
detail, this elision state is stored in the type field, but it is not
part of the type. pthread_mutexattr_gettype must return the exact
value that was passed to pthread_mutexattr_settype, nothing else.


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