POSIX Spin Locks

[joel.sherrill at oarcorp.com (Joel Sherrill)]

Hi,

I am looking at the POSIX spinlock specification and can't
see why it can't be implemented as some mutex variation.

Yes I understand the "test and set and poll if not available"
technique but the OpenGroup page doesn't require that behavior.

http://www.opengroup.org/onlinepubs/009695399/functions/pthread_spin_lock.html

====================================
The /pthread_spin_lock/() function shall lock the spin lock referenced 
by /lock/. The calling thread shall acquire the lock if it is not held 
by another thread. Otherwise, the thread shall spin (that is, shall not 
return from the /pthread_spin_lock/() call) until the lock becomes 
available. The results are undefined if the calling thread holds the 
lock at the time the call is made. The /pthread_spin_trylock/() function 
shall lock the spin lock referenced by /lock/ if it is not held by any 
thread. Otherwise, the function shall fail.
====================================

 From a user's perspective, a mutex lock does not return until the lock
becomes available. 

RTEMS SuperCore mutexes are very efficient.  I don't see the point of
not doing a simple implementation based upon SuperCore mutexes.

Any thoughts, comments, insights?

--joel