On Thu, Dec 22, 2011 at 10:59 AM, Peter Zijlstra [off-list ref] wrote:

On Wed, 2011-12-21 at 22:48 +0200, raz ben yehuda wrote:

quoted

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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