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Date: Fri, 22 Aug 2008 11:21:49 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-core] Fast userspace locks for native skin
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To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: xenomai-core <xenomai@xenomai.org>

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> decision (we could store the first pending thread priority in a
>> user/kernel shared area, with the complication that we would need
>> updating this priority if it ever changes, but to get the priority of
>> the current thread, we also need a syscall, moreover switching to
>> secondary mode).
> 
> I'm not thinking about the case where there is already someone waiting.
> That will need a kernel entry anyway (the low-prio waiter may sit on
> some other CPU...). But in case signaling always happens before pending,
> there is no need at all to consult the kernel.

In this case, you can avoid calling pthread_cond_signal at all... So, if
you are stupid enough to call pthread_cond_signal when no-one is
waiting, you deserve a syscall anyway.

-- 
                                                 Gilles.