From: Adam Lewis (adam.j.lewis_at_[hidden])
Date: 2006-08-01 10:48:20
The problem is you are storing pointers in the map, which are not in
the address space of proc#2. Check
http://ice.prohosting.com/newfunk/boost/libs/shmem/doc/html/shmem/limitations.html#shmem.offset_pointer
On 8/1/06, Pataki Szilard <ceelurd_at_[hidden]> wrote:
>
> Hello,
>
> I have a problem retrieving objects from a map placed in shared
> memory. I have two processes:
>
> proc#1: creates the shared memory, puts a map into it and populates it
> with objects
> proc#2: connects to the shared memory and tries to read out the
> objects from the map
>
> Whenever I try to read out the objects from the map, I get zeroes for
> the internal members (a, b).
>
> The class definition for the objects:
> --------------------------------------------------
> class ShmNode
> {
> private:
> int a;
> int b;
> public:
> ShmNode();
> ShmNode(int newa, int newb);
> ~ShmNode();
> void set(int newa, int newb);
> int getA();
> int getB();
> };
> --------------------------------------------------
>
> I'm posting the source codes for the two programs. I removed the
> synchronization stuff with semaphores for the sake of clarity:
>
> Proc#1:
> --------------------------------------------------
> #include <boost/shmem/named_shared_object.hpp>
> #include <boost/shmem/allocators/allocator.hpp>
> #include <boost/shmem/containers/vector.hpp>
> #include <boost/shmem/containers/map.hpp>
> #include <boost/shmem/sync/named_semaphore.hpp>
>
> #include <iostream>
> #include "../shmem/ShmNode.hpp"
>
> typedef std::pair<
> const int,
> ShmNode*>
> MyPair;
>
> typedef boost::shmem::allocator <
> MyPair,
>
> boost::shmem::named_shared_object::segment_manager>
> MyAlloc;
>
> typedef boost::shmem::map<
> const int,
> ShmNode*,
> std::less<const int>,
> MyAlloc>
> MyMap;
>
> int main()
> {
> boost::shmem::named_shared_object segment;
>
> segment.create("/myshmem", 20000);
>
> MyAlloc nodesAlloc(segment.get_segment_manager());
> std::less<const int> comparator;
>
> MyMap *table = segment.construct<MyMap>("table")(comparator,
> nodesAlloc);
>
> MyPair myPair1(1, new ShmNode(1,2));
> MyPair myPair2(2, new ShmNode(3,4));
> MyPair myPair3(3, new ShmNode(5,6));
>
> table->insert(myPair3);
> table->insert(myPair1);
> table->insert(myPair2);
>
> return 0;
> }
> --------------------------------------------------
>
> Proc#2
> --------------------------------------------------
> /* same includes */
>
> /* same typedefs */
>
> int main()
> {
> boost::shmem::named_shared_object segment;
> segment.open("/myshmem");
>
> MyMap *table = segment.find<MyMap>("table").first;
>
> std::cout << "table size: " << table->size() << std::endl;
>
> MyMap::iterator iter;
> for (iter = table->begin(); ; iter++)
> {
> if (iter == table->end())
> break;
> std::cout << iter->second->getA() << " " <<
> iter->second->getB() <<
> std::endl;
> }
> return 0;
> }
> --------------------------------------------------
>
>
> The problem once again: in proc#2, iter->second->getA() and
> iter->second->getB() return 0. If I put the same loop into proc#1, the
> correct values are returned. As a further hint, the size of the map
> object in proc#2 is returned correctly (=3).
>
> What am I doing wrong?
>
> Regards,
> Szilard
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