text: //
  // ssl/detail/openssl_init.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2017 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_SSL_DETAIL_OPENSSL_INIT_HPP
  #define BOOST_ASIO_SSL_DETAIL_OPENSSL_INIT_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include <boost/asio/detail/config.hpp>
  #include <cstring>
  #include <boost/asio/detail/memory.hpp>
  #include <boost/asio/detail/noncopyable.hpp>
  #include <boost/asio/ssl/detail/openssl_types.hpp>
  
  #include <boost/asio/detail/push_options.hpp>
  
  namespace boost {
  namespace asio {
  namespace ssl {
  namespace detail {
  
  class openssl_init_base
    : private noncopyable
  {
  protected:
    // Class that performs the actual initialisation.
    class do_init;
  
    // Helper function to manage a do_init singleton. The static instance of the
    // openssl_init object ensures that this function is always called before
    // main, and therefore before any other threads can get started. The do_init
    // instance must be static in this function to ensure that it gets
    // initialised before any other global objects try to use it.
    BOOST_ASIO_DECL static boost::asio::detail::shared_ptr<do_init> instance();
  
  #if !defined(SSL_OP_NO_COMPRESSION) \
    && (OPENSSL_VERSION_NUMBER >= 0x00908000L)
    // Get an empty stack of compression methods, to be used when disabling
    // compression.
    BOOST_ASIO_DECL static STACK_OF(SSL_COMP)* get_null_compression_methods();
  #endif // !defined(SSL_OP_NO_COMPRESSION)
         // && (OPENSSL_VERSION_NUMBER >= 0x00908000L)
  };
  
  template <bool Do_Init = true>
  class openssl_init : private openssl_init_base
  {
  public:
    // Constructor.
    openssl_init()
      : ref_(instance())
    {
      using namespace std; // For memmove.
  
      // Ensure openssl_init::instance_ is linked in.
      openssl_init* tmp = &instance_;
      memmove(&tmp, &tmp, sizeof(openssl_init*));
    }
  
    // Destructor.
    ~openssl_init()
    {
    }
  
  #if !defined(SSL_OP_NO_COMPRESSION) \
    && (OPENSSL_VERSION_NUMBER >= 0x00908000L)
    using openssl_init_base::get_null_compression_methods;
  #endif // !defined(SSL_OP_NO_COMPRESSION)
         // && (OPENSSL_VERSION_NUMBER >= 0x00908000L)
  
  private:
    // Instance to force initialisation of openssl at global scope.
    static openssl_init instance_;
  
    // Reference to singleton do_init object to ensure that openssl does not get
    // cleaned up until the last user has finished with it.
    boost::asio::detail::shared_ptr<do_init> ref_;
  };
  
  template <bool Do_Init>
  openssl_init<Do_Init> openssl_init<Do_Init>::instance_;
  
  } // namespace detail
  } // namespace ssl
  } // namespace asio
  } // namespace boost
  
  #include <boost/asio/detail/pop_options.hpp>
  
  #if defined(BOOST_ASIO_HEADER_ONLY)
  # include <boost/asio/ssl/detail/impl/openssl_init.ipp>
  #endif // defined(BOOST_ASIO_HEADER_ONLY)
  
  #endif // BOOST_ASIO_SSL_DETAIL_OPENSSL_INIT_HPP
  