linux-kernel - Re: Subject: [PATCH 2/2] priority System V Semaphores

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Date:	Thu, 22 Dec 2011 15:00:21 +0200
From:	Raz <raziebe@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Manfred Spraul <manfred@...orfullife.com>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lior Brafman <LBrafman@...z.com>,
	Torsten Scherer <TScherer@...z.com>,
	Rasty Slutsker <RSlutsker@...z.com>
Subject: Re: Subject: [PATCH 2/2] priority System V Semaphores

On Thu, Dec 22, 2011 at 10:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2011-12-21 at 22:48 +0200, raz ben yehuda wrote:
>> Vxworks is the use case. And there are plenty of companies with
>> vxWorks software and in i believe they will migrate sooner or later to
>> PreemptRT.  My current company uses old wrapper software that implements
>> vxWorks semaphores as system V semaphores. vxWorks semaphores have a priority
>> feature which is widely used.
>> I will probably change it some time in the future to posix semaphores , but posix
>> semaphores are implemented in glibc with futexes and atomic ops and i rather
>> mess with kernel and not glibc. funny , but true. glibc is harder.
>
> Semaphores are a fscking trainwreck for real-time programming. Don't use
> them, full stop. If you do, you're doing it wrong, it's really that
> simple.
>
> Use PI mutexes, which are already fully supported in glibc, no extra
> patching needed.
>
> Full NAK for any and all priority fudging for any semaphore
> implementation.
please correct me if am wrong, " posix semaphores
are implemented with pi mutex. ..?" I need a counting semaphore.
vxWorks priority/fifo semaphores are different from posix semaphores in
that the behaviour is defined on the semaphore and not the thread.
Q: what happens if I want one posix semahore to be FIFO and another
posix semaphore to be PRIO while both are used by the same
thread.should i to change policies each time ?
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