Re: std::multiset functionality support in boost interprocess headers

From: Murali Kishore (bmuralikishore_at_[hidden])
Date: 2024-09-28 07:49:57

Thanks Ion. I have tried the following sample, I see one  issue that "find"
is failing in the following sample.
#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/unordered_map.hpp>
#include <boost/interprocess/containers/set.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/containers/string.hpp>

#include <boost/interprocess/allocators/allocator.hpp>
#include <iostream>

// Define your types
using timer_id_t = int;

struct timer_instance_t {
    int id; // Example member
};

// Define allocators for shared memory
typedef boost::interprocess::allocator<timer_instance_t,
boost::interprocess::managed_shared_memory::segment_manager> TimerAllocator;
typedef boost::interprocess::allocator<std::pair<const timer_id_t,
timer_instance_t>,
boost::interprocess::managed_shared_memory::segment_manager> MapAllocator;

// Define the unordered_map type
typedef boost::unordered_map<timer_id_t, timer_instance_t,
std::hash<timer_id_t>, std::less<timer_id_t>, MapAllocator>
timer_instance_map_t;

int main() {
    using namespace boost::interprocess;

    // Create managed shared memory
    managed_shared_memory segment(open_or_create, "MySharedMemory", 65536);

    // Construct the unordered map in shared memory
    timer_instance_map_t* timer_instance_map =
segment.find_or_construct<timer_instance_map_t>("TimerInstanceMap")(10,
std::hash<timer_id_t>(), std::less<timer_id_t>(),
segment.get_segment_manager());

    // Allocate a timer_instance_t in shared memory
    timer_instance_t* instance =
segment.construct<timer_instance_t>("TimerInstance")();
    // Use emplace to insert the timer_instance_t pointer into the map
    timer_id_t id = 100;
    timer_instance_map->emplace(id, *instance); // Copy the allocated
instance into the map

    // Accessing the instance
    auto it = timer_instance_map->find(id);
    if (it != timer_instance_map->end()) {
        std::cout << "Found timer instance with id: " << it->second.id <<
std::endl;
    } else {
        std::cout << "Timer instance not found." << std::endl;
    }

for (const auto& pair : *timer_instance_map) {
std::cout <<"Timer Id: " <<  pair.first <<", Timer Instance Id: " <<
pair.second.id<< std::endl;
      }

    // Cleanup: You may want to remove the shared memory segment
    shared_memory_object::remove("MySharedMemory");

    return 0;
}

output:
Timer Instance not found.
Timer Id: 100, Timer Instance Id: 0

need help in understanding why find is failing.

Regards,
Murali Kishore

On Mon, Sep 9, 2024 at 8:42 PM Ion Gaztañaga <igaztanaga_at_[hidden]> wrote:

> El 09/09/2024 a las 15:18, Murali Kishore via Boost escribió:
> > Hi all,
> >
> > I see multiset is not present in boost interprocess, so I tried to use a
> > "set" with a customized comparator to achieve multiset functionality.
>
> You can use any Boost.Container container with Boost.Interprocess,
> including multiset.
>
> Boost.Interprocess own container aliases will be deprecated soon, since
> they only forward to Boost.Container. I'll maintain those container
> header inside Interprocess for backwards compatibility for several Boost
> releases but in the end they will be removed.
>
> Best,
>
> Ion
>
>

-- 
Regards,
Murali Kishore