Re: NPTL mutex and the scheduling priority

On Thu, Sep 07, 2006 at 05:11:58PM +0900, Atsushi Nemoto wrote:
Three months after, I have tried kernel 2.6.18 with recent glibc. I
got desired results for pthread_mutex_unlock and
pthread_cond_broadcast, with PI-mutex.

But pthread_cond_signal and sem_post still wakeup a thread in FIFO
order, as you can guess.

With the plist patch (applied by hand), I can get desired behavior.
Thank you. But It seems the patch lacks reordering on priority
changes.

Yes, either something like the plist patch for FUTEX_WAKE etc. or, if that
proves to be too slow for the usual case (non-RT threads), FIFO wakeup
initially and conversion to plist wakeup whenever first waiter with realtime
priority is added, is still needed. That will cure e.g. non-PI
pthread_mutex_unlock and sem_post. For pthread_cond_{signal,broadcast} we
need further kernel changes, so that the condvar's internal lock can be
always a PI lock.

<off_topic>
BTW, If I tried to create a PI mutex on a kernel without PI futex
support, pthread_mutexattr_setprotocol(PTHREAD_PRIO_INHERIT) returned
0 and pthread_mutex_init() returned ENOTSUP. This is not a right
behavior according to the manual ...
</off_topic>

Why?
POSIX doesn't forbid ENOTSUP in pthread_mutex_init to my knowledge.

Jakub
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