sys/barrier.3

   1 .Dd May 26, 2004
   2 .Dt BARRIER 3
   3 .Os Darwin
   4 .Sh NAME
   5 .Nm OSMemoryBarrier
   6 .Nd memory barrier to order loads and stores
   7 .Sh LIBRARY
   8 .Lb libc
   9 .Sh SYNOPSIS
  10 .In libkern/OSAtomic.h
  11 .Ft void
  12 .Fn OSMemoryBarrier "void"
  13 .Sh DESCRIPTION
  14 .Fn OSMemoryBarrier
  15 strictly orders memory accesses in a weakly ordered memory model such as with PowerPC,
  16 by creating a barrier.  All loads and stores executed in sequential program order before
  17 the barrier will complete with respect to the memory coherence mechanism, before any
  18 load or store executed after the barrier.  Used with an atomic operation, the barrier
  19 can be used to create custom synchronization protocols as an alternative to the
  20 spinlock or queue/dequeue operations.  Note that this barrier does not order uncached loads
  21 and stores.  On a uniprocessor, the barrier operation is typically optimized into a nop.
  22 .Sh SEE ALSO
  23 .Xr atomic 3 ,
  24 .Xr atomicqueue 3 ,
  25 .Xr spinlock 3