Ticket #5548: shm.cpp

//
// Purpose: Play arround with shared memory and the permissions to allocate it
//

#include <sys/shm.h>                    // shmget,...
#include <iostream>
#include <string>
#include <cerrno>                       // errno
#include <cstring>                      // strerror
#include <cstdlib>                      // system

#include <boost/cstdint.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/interprocess/managed_shared_memory.hpp>

static const int invalid_shm_id = -1;
static const int invalid_shm_pointer = -1;

static const int shm_key = 0x12345;
static const int shm_size = 0x1000;
static const std::string shm_key_for_boost =
    boost::lexical_cast<std::string>(shm_key);

static const int shm_boost_margin = 0x100;


boost::uint8_t * shm_create_unix(int & shm_id)
{
    //
    // create global shared memory and get an id of it
    // (identified by the given key)
    //
    shm_id = shmget(shm_key,
                    shm_size,
                    0600 | IPC_CREAT | IPC_EXCL);

    if (shm_id == invalid_shm_id)
    {
        std::cerr << "Could not get global shared memory for key="
                  << shm_key
                  << ": " << strerror(errno)
                  << std::endl;
        return 0;
    }

    //
    // attach the global shared memory
    // (associated with the given id, not the key)
    //
    boost::uint8_t * shm =
        static_cast<boost::uint8_t *>(shmat(shm_id,
                                            static_cast<void*>(0),
                                            0));

    if (shm == reinterpret_cast<void *>(invalid_shm_pointer))
    {
        std::cerr << "Could not attach global shared memory for id="
                  << boost::lexical_cast<std::string>(shm_id)
                  << ", key="
                  << boost::lexical_cast<std::string>(shm_key)
                  << ": " << strerror(errno)
                  << std::endl;
        return 0;
    }

    return shm;
}

void shm_free_unix(boost::uint8_t * shm, int shm_id)
{
    int ret = shmdt(shm);

    if (ret == -1)
    {
        std::cerr << "Detaching of shared memory (0x"
                  << std::hex << shm << std::dec
                  << ") failed. id=" << shm_id
                  << ": " << strerror(errno)
                  << std::endl;
        return;
    }

    ret = shmctl(shm_id, IPC_RMID, NULL);

    if (ret != 0)
    {
        std::cerr << "Deleting of shared memory failed. id="
                  << boost::lexical_cast<std::string>(shm_id)
                  << ": " << strerror(errno)
                  << std::endl;
    }
}

boost::uint8_t * shm_create_boost()
{
   using namespace boost::interprocess;

   //A special shared memory from which we are
   //able to allocate raw memory buffers.
   //First remove any old shared memory of the same name, create 
   //the shared memory segment and initialize needed resources
   shared_memory_object::remove(shm_key_for_boost.c_str());

   void * shm = 0;

   try
   {
       // boost also needs some private space in the shared memory
       managed_shared_memory segment(create_only,
                                     shm_key_for_boost.c_str(),
                                     shm_size+shm_boost_margin);

      //Allocate a portion of the segment
      shm = segment.allocate(shm_size);
   }
   catch(...)
   {
       shared_memory_object::remove(shm_key_for_boost.c_str());
       throw;
   }

   return static_cast<boost::uint8_t *>(shm);
}

void shm_free_boost(boost::uint8_t * shm)
{
   using namespace boost::interprocess;

   try
   {
       managed_shared_memory segment(open_only,
                                     shm_key_for_boost.c_str());

       segment.deallocate(shm);
   }
   catch(...)
   {
       shared_memory_object::remove(shm_key_for_boost.c_str());
       throw;
   }

   shared_memory_object::remove(shm_key_for_boost.c_str());
}

int main(int argc, char * argv[])
{
    if (argc <= 1)
    {
        std::cout << "unix way:" << std::endl;

        int shm_id = invalid_shm_id;

        boost::uint8_t * const shm = shm_create_unix(shm_id);

        std::cout << "Got shm=" << static_cast<void *>(shm) << std::endl;

        system("ipcs -m");

        shm_free_unix(shm, shm_id);
    }
    else
    {
        std::cout << "Boost way:" << std::endl;

        boost::uint8_t * const shm = shm_create_boost();

        std::cout << "Got shm=" << static_cast<void *>(shm) << std::endl;

        system("ipcs -m");

        shm_free_boost(shm);
    }

    return 0;
}