text: //
  // detail/gcc_arm_fenced_block.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  //
  // Distributed under the Boost Software License, Version 1.0. (See accompanying
  // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  //
  
  #ifndef BOOST_ASIO_DETAIL_GCC_ARM_FENCED_BLOCK_HPP
  #define BOOST_ASIO_DETAIL_GCC_ARM_FENCED_BLOCK_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include <boost/asio/detail/config.hpp>
  
  #if defined(__GNUC__) && defined(__arm__)
  
  #include <boost/asio/detail/push_options.hpp>
  
  namespace boost {
  namespace asio {
  namespace detail {
  
  class gcc_arm_fenced_block
    : private noncopyable
  {
  public:
    // Constructor.
    gcc_arm_fenced_block()
    {
      barrier();
    }
  
    // Destructor.
    ~gcc_arm_fenced_block()
    {
      barrier();
    }
  
  private:
    static void barrier()
    {
  #if defined(__ARM_ARCH_4__) \
      || defined(__ARM_ARCH_4T__) \
      || defined(__ARM_ARCH_5__) \
      || defined(__ARM_ARCH_5E__) \
      || defined(__ARM_ARCH_5T__) \
      || defined(__ARM_ARCH_5TE__) \
      || defined(__ARM_ARCH_5TEJ__) \
      || defined(__ARM_ARCH_6__) \
      || defined(__ARM_ARCH_6J__) \
      || defined(__ARM_ARCH_6K__) \
      || defined(__ARM_ARCH_6Z__) \
      || defined(__ARM_ARCH_6ZK__) \
      || defined(__ARM_ARCH_6T2__)
  # if defined(__thumb__)
      // This is just a placeholder and almost certainly not sufficient.
      __asm__ __volatile__ ("" : : : "memory");
  # else // defined(__thumb__)
      int a = 0, b = 0;
      __asm__ __volatile__ ("swp %0, %1, [%2]"
          : "=&r"(a) : "r"(1), "r"(&b) : "memory", "cc");
  # endif // defined(__thumb__)
  #else
      // ARMv7 and later.
      __asm__ __volatile__ ("dmb" : : : "memory");
  #endif
    }
  };
  
  } // namespace detail
  } // namespace asio
  } // namespace boost
  
  #include <boost/asio/detail/pop_options.hpp>
  
  #endif // defined(__GNUC__) && defined(__arm__)
  
  #endif // BOOST_ASIO_DETAIL_GCC_ARM_FENCED_BLOCK_HPP
  