boost_1_45_0/libs/interprocess/example/doc_scoped_ptr.cpp

//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2006-2009. 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)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////
#include <boost/interprocess/detail/config_begin.hpp>
#include <boost/interprocess/detail/workaround.hpp>
//[doc_scoped_ptr
#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/smart_ptr/scoped_ptr.hpp>
//<-
#include "../test/get_process_id_name.hpp"
//->

using namespace boost::interprocess;

class my_class
{};

class my_exception
{};

//A functor that destroys the shared memory object
template<class T>
class my_deleter
{
   private:
   //A typedef to save typing
   typedef managed_shared_memory::segment_manager segment_manager;
   //This my_deleter is created in the stack, not in shared memory,
   //so we can use raw pointers
   segment_manager *mp_segment_manager;

   public:
   //This typedef will specify the pointer type that
   //scoped_ptr will store
   typedef T *pointer;
   //Constructor
   my_deleter(segment_manager *s_mngr)
   : mp_segment_manager(s_mngr){}

   void operator()(pointer object_to_delete)
   {  mp_segment_manager->destroy_ptr(object_to_delete);  }
};

int main ()
{
   //Create shared memory
   //Remove shared memory on construction and destruction
   struct shm_remove
   {
   //<-
   #if 1
      shm_remove() { shared_memory_object::remove(test::get_process_id_name()); }
      ~shm_remove(){ shared_memory_object::remove(test::get_process_id_name()); }
   #else
   //->
      shm_remove() { shared_memory_object::remove("MySharedMemory"); }
      ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }
   //<-
   #endif
   //->
   } remover;

   //<-
   #if 1
   managed_shared_memory shmem(create_only, test::get_process_id_name(), 10000);
   #else
   //->
   managed_shared_memory shmem(create_only, "MySharedMemory", 10000);
   //<-
   #endif
   //->

   //In the first try, there will be no exceptions
   //in the second try we will throw an exception
   for(int i = 0; i < 2; ++i){
      //Create an object in shared memory
      my_class * my_object = shmem.construct<my_class>("my_object")();
      my_class * my_object2 = shmem.construct<my_class>(anonymous_instance)();
      shmem.destroy_ptr(my_object2);
      
      //Since the next shared memory allocation can throw
      //assign it to a scoped_ptr so that if an exception occurs
      //we destroy the object automatically
      my_deleter<my_class> d(shmem.get_segment_manager());

      try{
         scoped_ptr<my_class, my_deleter<my_class> > s_ptr(my_object, d);
         //Let's emulate a exception capable operation
         //In the second try, throw an exception
         if(i == 1){
            throw(my_exception());
         }
         //If we have passed the dangerous zone
         //we can release the scoped pointer
         //to avoid destruction
         s_ptr.release();
      }
      catch(const my_exception &){}
      //Here, scoped_ptr is destroyed
      //so it we haven't thrown an exception
      //the object should be there, otherwise, destroyed
      if(i == 0){
         //Make sure the object is alive
         if(!shmem.find<my_class>("my_object").first){
            return 1;
         }
         //Now we can use it and delete it manually
         shmem.destroy<my_class>("my_object");
      }
      else{
         //Make sure the object has been deleted
         if(shmem.find<my_class>("my_object").first){
            return 1;
         }
      }
   }
   return 0;
}
//]
#include <boost/interprocess/detail/config_end.hpp>