CODEWITHSUNDEEP
c++boostshared-memory
PrimeOfKnights
PrimeOfKnights

Reputation: 423

Best way to dump data from boost shared memory

I have 2 application. One writes high frequency data to boost managed shared memory, data struct being boost deque. 

typedef boost::interprocess::allocator<REALTIME_INFO, boost::interprocess::managed_shared_memory::segment_manager> ShmemAllocator;
typedef boost::interprocess::deque<REALTIME_INFO, ShmemAllocator> MyDeque;

boost::interprocess::managed_shared_memory segment(boost::interprocess::open_or_create, "MySharedMemory",50000000); 
const ShmemAllocator alloc_inst (segment.get_segment_manager());
MyDeque *Mydeque;
Mydeque = segment.find_or_construct<MyDeque>("myd")(alloc_inst);//first ctor parameter

if(Mydeque->size() < 150000){   
    Mydeque->push_back(rtinfo);
}
else{
    Mydeque->pop_front();
    Mydeque->push_back(rtinfo);
}

My second application is a Qt application when pressed button reads from the shared memory and writes to a csv file. Since the data is huge I cannot write the data directly from shared memory so I tried memcpy. I could only get the first value and remaining were garbage. 

managed_shared_memory segment (open_only, "MySharedMemory");
MyDeque *Mydeque = segment.find<MyDeque>("myd").first;

After getting the first pointer I tried to copy it to another MyDeque but I can only access the first pointer and cannot iterate remaining data.

memcpy(Mydeque_new, &Mydeque, Mydeque->size()*sizeof(REALTIME_INFO));

Can anyone suggest a better way to copy data from shared memory to a local memory.

Upvotes: 2

Views: 720

Answers (1)

sehe
sehe

Reputation: 392999

memcpy(Mydeque_new, &Mydeque, Mydeque->size()*sizeof(REALTIME_INFO));

This is big fat Undefined Behaviour because deque<> is not a POD type. In fact, even the elements data is not contiguous in memory, so you can't even memcpy that.

Upvotes: 2

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