osx man page for barrier

BARRIER(3)						   BSD Library Functions Manual 						BARRIER(3)

NAME
     OSMemoryBarrier -- memory barrier to order loads and stores

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <libkern/OSAtomic.h>

     void
     OSMemoryBarrier(void);

DESCRIPTION
     OSMemoryBarrier() strictly orders memory accesses in a weakly ordered memory model such as with PowerPC, by creating a barrier.  All loads
     and stores executed in sequential program order before the barrier will complete with respect to the memory coherence mechanism, before any
     load or store executed after the barrier.	Used with an atomic operation, the barrier can be used to create custom synchronization protocols
     as an alternative to the spinlock or queue/dequeue operations.  Note that this barrier does not order uncached loads and stores.  On a
     uniprocessor, the barrier operation is typically optimized into a nop.

SEE ALSO
     atomic(3), spinlock(3)

Darwin								   May 26, 2004 							    Darwin