[lttng-dev] urcu rfc: privatize urcu/futex.h

[Mathieu Desnoyers]

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> (Added a CC email address)
> 
> On 08/08/2012 09:03 AM, Lai Jiangshan wrote:
> > On 08/07/2012 10:06 PM, Mathieu Desnoyers wrote:
> >> Hi Lai,
> >>
> >> * Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> >>> futex.h is in urcu/, it means it can be used by users out of the library.
> >>>
> >>> But
> >>>
> >>> If the user's system has futex, he should use #include <linux/futex.h>.
> >>> If the user's system don't have futex, it is not good that if the user
> >>> use this compat_futex.
> >>>
> >>> Because the compat_futex_async()'s behavior is different from the
> >>> futex in linux.  If the caller don't change the value of @uaddr, the
> >>> futex(FUTEX_WAKE) in linux can also wake a thread, but
> >>> compat_futex_async() don't.  (I guess no one use this behavior, but if
> >>> there are someone, we give them a wrong thing)
> >>
> >> Hrm, passing a NULL uaddr parameter is really not the targeted use-case.
> >> We could probably just document that uaddr should not be NULL when using
> >> compat_futex ?
> > 
> > Sorry, I wanted to show you such un-normal behavior:
> > 
> > /* keep the value of *uaddr unchanged, wake up a thread to do something */
> > futex(FUTEX_WAKE, uaddr, ...).
> > 
> > This can't not wake up any thread for current compat_futex_async() implement.
> > But the sys_futex() can.
> > 
> > 
> 
> It is hard to implement compat_futex_async() to make its behavior compatible
> with sys_futex().(I don't like the two alternatives too, I just wrote
> what I have thought) so I sent rfc email to suggest to privatize
> urcu/futex.h.

I don't think this issue has been taken care of, am I correct ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com