spin locks

> spin-lock.patch
> 
> 	I'm not sure if this is really useful, but it seems stupid to have
> 	a backend wasting cpu cycles in a busy loop while the process which
> 	should release the lock is waiting for the cpu. So I added a call
> 	to process_yield() if the spin lock can't obtained.
> 	This has been implemented and tested only on Linux. I don't know if
> 	other OS have process_yield(). If someone can check please do it.

Massimo brings up a good point.  Most of our s_lock.h locking does asm
mutex loops looking for a lock.  Unless we are using a multi-cpu
machine, there is no way this is going to change while we are spinning.

Linux has process_yield(), but most OS's don't.  Is there a
platform-independent way to relinquish the cpu if the first attempt at
the spinlock fails?  Would a select() of 1 microsecond work?

-- 
Bruce Momjian
maillist@candle.pha.pa.us