linux-kernel - question about __raw_spin

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Date:	Wed, 6 Sep 2006 10:25:15 +0200
From:	Roland Kuhn <rkuhn@....physik.tu-muenchen.de>
To:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: question about __raw_spin_lock()

Dear experts!

Trying to inform myself about the locking possibilities on i386, I  
read linux/include/asm-i386/spinlock.h. I'm no expert on inline  
assembly, so I'm asking myself what would happen on a very big system  
if more than 128 threads are waiting on the same raw_spinlock_t.  
Would the 129th locker erroneously succeed immediately?

As a side note: I was looking because I have to implement a simple  
lock between processes in shared memory, and unfortunately I cannot  
use the NPTL :-( SysV semaphores presumably are much too heavy to  
protect simple linked list operations (no scanning of the list under  
the lock, just inserting on one end and removing from the other).  
Does anybody have a better idea than spinning in user space---with a  
nanosleep now and then---or does this have problems I'm not aware of?

Thanks for your help,

                     Roland

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