text: /*
   * $Id: pa_memorybarrier.h 1240 2007-07-17 13:05:07Z bjornroche $
   * Portable Audio I/O Library
   * Memory barrier utilities
   *
   * Author: Bjorn Roche, XO Audio, LLC
   *
   * This program uses the PortAudio Portable Audio Library.
   * For more information see: http://www.portaudio.com
   * Copyright (c) 1999-2000 Ross Bencina and Phil Burk
   *
   * Permission is hereby granted, free of charge, to any person obtaining
   * a copy of this software and associated documentation files
   * (the "Software"), to deal in the Software without restriction,
   * including without limitation the rights to use, copy, modify, merge,
   * publish, distribute, sublicense, and/or sell copies of the Software,
   * and to permit persons to whom the Software is furnished to do so,
   * subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be
   * included in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
   * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
   * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
   * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
   * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   */
  
  /*
   * The text above constitutes the entire PortAudio license; however, 
   * the PortAudio community also makes the following non-binding requests:
   *
   * Any person wishing to distribute modifications to the Software is
   * requested to send the modifications to the original developer so that
   * they can be incorporated into the canonical version. It is also 
   * requested that these non-binding requests be included along with the 
   * license above.
   */
  
  /**
   @file pa_memorybarrier.h
   @ingroup common_src
  */
  
  /****************
   * Some memory barrier primitives based on the system.
   * right now only OS X, FreeBSD, and Linux are supported. In addition to providing
   * memory barriers, these functions should ensure that data cached in registers
   * is written out to cache where it can be snooped by other CPUs. (ie, the volatile
   * keyword should not be required)
   *
   * the primitives that must be defined are:
   *
   * PaUtil_FullMemoryBarrier()
   * PaUtil_ReadMemoryBarrier()
   * PaUtil_WriteMemoryBarrier()
   *
   ****************/
  
  #if defined(__APPLE__)
  #   include <libkern/OSAtomic.h>
      /* Here are the memory barrier functions. Mac OS X only provides
         full memory barriers, so the three types of barriers are the same,
         however, these barriers are superior to compiler-based ones. */
  #   define PaUtil_FullMemoryBarrier()  OSMemoryBarrier()
  #   define PaUtil_ReadMemoryBarrier()  OSMemoryBarrier()
  #   define PaUtil_WriteMemoryBarrier() OSMemoryBarrier()
  #elif defined(__GNUC__)
      /* GCC >= 4.1 has built-in intrinsics. We'll use those */
  #   if (__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1)
  #      define PaUtil_FullMemoryBarrier()  __sync_synchronize()
  #      define PaUtil_ReadMemoryBarrier()  __sync_synchronize()
  #      define PaUtil_WriteMemoryBarrier() __sync_synchronize()
      /* as a fallback, GCC understands volatile asm and "memory" to mean it
       * should not reorder memory read/writes */
      /* Note that it is not clear that any compiler actually defines __PPC__,
       * it can probably removed safely. */
  #   elif defined( __ppc__ ) || defined( __powerpc__) || defined( __PPC__ )
  #      define PaUtil_FullMemoryBarrier()  asm volatile("sync":::"memory")
  #      define PaUtil_ReadMemoryBarrier()  asm volatile("sync":::"memory")
  #      define PaUtil_WriteMemoryBarrier() asm volatile("sync":::"memory")
  #   elif defined( __i386__ ) || defined( __i486__ ) || defined( __i586__ ) || \
           defined( __i686__ ) || defined( __x86_64__ )
  #      define PaUtil_FullMemoryBarrier()  asm volatile("mfence":::"memory")
  #      define PaUtil_ReadMemoryBarrier()  asm volatile("lfence":::"memory")
  #      define PaUtil_WriteMemoryBarrier() asm volatile("sfence":::"memory")
  #   else
  #      ifdef ALLOW_SMP_DANGERS
  #         warning Memory barriers not defined on this system or system unknown
  #         warning For SMP safety, you should fix this.
  #         define PaUtil_FullMemoryBarrier()
  #         define PaUtil_ReadMemoryBarrier()
  #         define PaUtil_WriteMemoryBarrier()
  #      else
  #         error Memory barriers are not defined on this system. You can still compile by defining ALLOW_SMP_DANGERS, but SMP safety will not be guaranteed.
  #      endif
  #   endif
  #elif (_MSC_VER >= 1400) && !defined(_WIN32_WCE)
  #   include <intrin.h>
  #   pragma intrinsic(_ReadWriteBarrier)
  #   pragma intrinsic(_ReadBarrier)
  #   pragma intrinsic(_WriteBarrier)
  #   define PaUtil_FullMemoryBarrier()  _ReadWriteBarrier()
  #   define PaUtil_ReadMemoryBarrier()  _ReadBarrier()
  #   define PaUtil_WriteMemoryBarrier() _WriteBarrier()
  #elif defined(_WIN32_WCE)
  #   define PaUtil_FullMemoryBarrier()
  #   define PaUtil_ReadMemoryBarrier()
  #   define PaUtil_WriteMemoryBarrier()
  #elif defined(_MSC_VER) || defined(__BORLANDC__)
  #   define PaUtil_FullMemoryBarrier()  _asm { lock add    [esp], 0 }
  #   define PaUtil_ReadMemoryBarrier()  _asm { lock add    [esp], 0 }
  #   define PaUtil_WriteMemoryBarrier() _asm { lock add    [esp], 0 }
  #else
  #   ifdef ALLOW_SMP_DANGERS
  #      warning Memory barriers not defined on this system or system unknown
  #      warning For SMP safety, you should fix this.
  #      define PaUtil_FullMemoryBarrier()
  #      define PaUtil_ReadMemoryBarrier()
  #      define PaUtil_WriteMemoryBarrier()
  #   else
  #      error Memory barriers are not defined on this system. You can still compile by defining ALLOW_SMP_DANGERS, but SMP safety will not be guaranteed.
  #   endif
  #endif
  