text: // Copyright 2018, 2020 Peter Dimov
  // Distributed under the Boost Software License, Version 1.0.
  // https://www.boost.org/LICENSE_1_0.txt)
  
  #include <boost/shared_ptr.hpp>
  #include <boost/weak_ptr.hpp>
  #include <boost/smart_ptr/detail/lightweight_thread.hpp>
  #include <boost/bind/bind.hpp>
  #include <boost/core/lightweight_test.hpp>
  
  static boost::shared_ptr<int> sp( new int );
  static boost::weak_ptr<int> wp( sp );
  
  void f1( int n )
  {
      for( int i = 0; i < n; ++i )
      {
          boost::weak_ptr<int> p1( wp );
  
          BOOST_TEST( !wp.expired() );
          BOOST_TEST( wp.lock() != 0 );
      }
  }
  
  void f2( int n )
  {
      for( int i = 0; i < n; ++i )
      {
          boost::weak_ptr<int> p1( wp );
  
          BOOST_TEST( wp.expired() );
          BOOST_TEST( wp.lock() == 0 );
      }
  }
  
  int main()
  {
      int const N = 100000; // iterations
      int const M = 8;      // threads
  
      boost::detail::lw_thread_t th[ M ] = {};
  
      for( int i = 0; i < M; ++i )
      {
          boost::detail::lw_thread_create( th[ i ], boost::bind( f1, N ) );
      }
  
      for( int i = 0; i < M; ++i )
      {
          boost::detail::lw_thread_join( th[ i ] );
      }
  
      BOOST_TEST_EQ( sp.use_count(), 1 );
      BOOST_TEST_EQ( wp.use_count(), 1 );
  
      sp.reset();
  
      BOOST_TEST_EQ( sp.use_count(), 0 );
      BOOST_TEST_EQ( wp.use_count(), 0 );
  
      for( int i = 0; i < M; ++i )
      {
          boost::detail::lw_thread_create( th[ i ], boost::bind( f2, N ) );
      }
  
      for( int i = 0; i < M; ++i )
      {
          boost::detail::lw_thread_join( th[ i ] );
      }
  
      wp.reset();
  
      return boost::report_errors();
  }
  