It seems you just don't have enough memory. You can assume that you should not, as individual distributions do not occupy the volume of space.
But memory fragmentation can do this: if there is sufficient “padding” or “overhead” in shared memory objects, you can exit the contiguous space.
Either save the data in a pre-selected vector (for example,), or use one of the more intelligent distribution algorithms between processes:
The simplest way to resolve it in this case, apparently, will simply make the shared memory area twice as large (the minimum size is a 4K memory page on most systems).
I just used 2*size and the tests completed.
Update / Corrections
I just checked that something really does the "vector way" much more efficiently: replacing std::map with boost flat_map gives you vector storage.
The big difference is that each node on the map is dynamically allocated, which leads to a fixed invoice linearly consuming available memory.
Observations
- There was significant upfront overhead, consuming 320 bytes before anything happened.
- with
flat_map , you also keep the vector capacity up, you see that you can only win a small extra storage efficiency.
The above chart was created at the output of the next program. Look for the get_free_memory() calls. To switch the map implementation, just change #if 0 to #if 1 . (Notice how I cleared some of the code that was useless for reuse and used exceptions to control the flow).
#include <boost/interprocess/managed_shared_memory.hpp> #include <boost/interprocess/containers/map.hpp> #include <boost/interprocess/allocators/allocator.hpp> #include <boost/interprocess/containers/string.hpp> #include <boost/interprocess/containers/flat_map.hpp> #include <boost/interprocess/exceptions.hpp> #include <functional> #include <utility> #include <iostream> #include <string> #define space_name "MySharedMemory" int main () { using namespace boost::interprocess; //Remove shared memory on construction and destruction struct shm_remove { shm_remove() { shared_memory_object::remove(space_name); } ~shm_remove(){ shared_memory_object::remove(space_name); } } remover; typedef int KeyType; typedef boost::interprocess::managed_shared_memory::allocator<char>::type char_allocator; //typedef boost::interprocess::allocator<char, boost::interprocess::managed_shared_memory::segment_manager> char_allocator; //typedef boost::interprocess::basic_string<char, std::char_traits<char>, char_allocator> shm_string; struct certificateStorage{ int certificate_id; certificateStorage( int _certificate_id, const char* _certificate, const char* _key, const char_allocator &al) : certificate_id(_certificate_id) {} }; #if 0 // STL typedef std::pair<const int, certificateStorage> certValueType; typedef allocator<certValueType, boost::interprocess::managed_shared_memory::segment_manager> certShmemAllocator; typedef map<KeyType, certificateStorage, std::less<KeyType>, certShmemAllocator> certSHMMap; #else // FLAT_MAP typedef std::pair<int, certificateStorage> certValueType; // not const key for flat_map typedef allocator<certValueType, boost::interprocess::managed_shared_memory::segment_manager> certShmemAllocator; typedef boost::container::flat_map<KeyType, certificateStorage, std::less<KeyType>, certShmemAllocator> certSHMMap; #endif std::cout << "\n\n\nStarting the program.\n\n\n"; const int numentries = 20; const char* elementName = "mymap"; int size = sizeof(certificateStorage) * numentries + 1000; int runningsize = 0; std::cout << "SHM size is " <<size<< " bytes \n"; try{ managed_shared_memory shm_segment(create_only, space_name/*segment name*/, size); certShmemAllocator alloc_inst (shm_segment.get_segment_manager()); char_allocator ca(shm_segment.get_allocator<char>()); certSHMMap *mymap = shm_segment.find_or_construct<certSHMMap>(elementName) (std::less<int>(), alloc_inst); mymap->reserve(numentries); for(int i = 0; i < numentries; i++){ std::cout << "Free memory: " << shm_segment.get_free_memory() << "\n"; certificateStorage thisCert(i, "", "", ca); std::cout << "Created object.\n"; mymap->insert(certValueType(i, thisCert)); std::cout << "Inserted object. " << i <<" size is " <<sizeof(thisCert) << " \n"; runningsize += sizeof(thisCert) ; std::cout << "SHM Current size is " << runningsize << " / " << size << "\n"; } std::cout << "\n\nDone Inserting\nStarting output\n"; for(int i = 0; i < numentries; i++){ certificateStorage tmp = mymap->at(i); std::cout << "The key is: " << i << " And the value is: " << tmp.certificate_id << "\n"; } } catch(boost::interprocess::interprocess_exception &ex){ std::cout << "\n shm space wont load wont load\n"; std::cout << "\n Why: " << ex.what() << "\n"; } }