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Re: [PATCH 2.5.64] Real-time futexes (priority inheritance/protection/robustsupport) take 4



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Inaky Perez-Gonzalez wrote:

> - Does not modify original futexes - a new interface is added

This is the killer.

If it's not the same futex interface which is used it is not possible to
use the non-rt version of the libpthread and the rt version on the same
system.  The whole thing is complicated by statically binaries.

The problem is obvious: what do you do for mutex/condvars/barriers/etc
which are in shared memory and created with the pshared bit set?  If it
is not possible to use the same futex kernel interface, how would you
select the right kernel interface to use?  At the side of the
process(es) which did not create the sync object there is no indication
whatsoever whether the object is in shared memory or not.

Therefore, any solution must fit seemlessly into the existing futex
interface.  It might be possible to have the function call which
actually initializes the object to do some more work and tell the kernel
something.  But if the static initializers are used not even this is
possible.  For pshared object it is possible since there is no static
initializer to create such objects.


If you insist on not having a unified object the only possibility is to
have separate libpthreads.  Because of the confusion this creates and
the support nightmare I strongly oppose this but of course cannot
prevent it from happening in a separate project.

- -- 
- --------------.                        ,-.            444 Castro Street
Ulrich Drepper \    ,-----------------'   \ Mountain View, CA 94041 USA
Red Hat         `--' drepper at redhat.com `---------------------------
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