.Dd May 26, 2004
.Dt BARRIER 3
.Os Darwin
.Sh NAME
.Nm OSMemoryBarrier
.Nd memory barrier to order loads and stores
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In libkern/OSAtomic.h
.Ft void
.Fn OSMemoryBarrier "void"
.Sh DESCRIPTION
.Fn 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.
.Sh SEE ALSO
.Xr atomic 3 ,
.Xr spinlock 3