I have been trying a few solutions using the boost interprocess library with a map and now a multi_index_container in shared memory. With the multi_index_container, is there any way other than to iterate over the values returned from equal_range. I was hoping to retrieve a subset of results from my non_unique index (station name e.g. ST0012345) and then find/get the actual measurement type I need (e.g. Temperature).
I need to retrieve the unique pointID value for the measurement point (e.g. ST0012345SMD10000456.VoltsA = pointID - 45789) to insert the measurement value into a data Historian. I liked the idea of multi_index_container as our message payloads contain ~100 to 200 measurements for the one station in an array so I thought I could do one call to the shared memory container which will contain 500,000+ items and then lookup each measurement point from a much smaller list using the long unique string name.
It seems from the reading I have done that I may only be able to iterate over the smaller list returned from the multi_index_container rather than do a get/find.
If that is the case, am I better off to stick to my original shared memory map solution (which I have working) which as I said contains 500,000+ items of longish strings to match on to retrieve the pointID required by our data historian. There is a high data rate with 200 points being processed per second (I found my data map lookup could reach 2000 lookups per second in a test environment).
Also, if I do use the map, is there any harm in having several maps in shared memory e.g. a map for Sydney stations (~300,000 points), a map for Newcastle stations (~200,000 points).
Below is the code for my program which is retrieving items from a seperate process that created the multi_index_container.
using namespace boost::interprocess;
using namespace System;
namespace bmi = boost::multi_index;
typedef managed_shared_memory::allocator<char>::type char_allocator;
typedef basic_string<char, std::char_traits<char>, char_allocator>shm_string;
struct tag
{
shm_string name;
shm_string stn;
shm_string mtype;
int id;
tag( const char *name_
, const char_allocator &a
, const char *stn_
, const char_allocator &b
, const char *mtype_
, const char_allocator &d
, int id_)
: name(name_, a),
stn(stn_, b),
mtype(mtype_, d),
id(id_)
{}
};
struct name{};
struct stn{};
struct mtype{};
struct id{};
typedef bmi::multi_index_container<
tag,
bmi::indexed_by<
bmi::ordered_unique
<bmi::tag<name>, BOOST_MULTI_INDEX_MEMBER(tag,shm_string,name)>,
bmi::ordered_non_unique<
bmi::tag<stn>,BOOST_MULTI_INDEX_MEMBER(tag,shm_string,stn)> >,
managed_shared_memory::allocator<tag>::type
> tag_set;
typedef tag_set::iterator iterator;
int main(array<System::String ^> ^args)
{
try{
managed_shared_memory segment(open_only,"MySharedMemory");
offset_ptr<tag_set> es = segment.find<tag_set>("My MultiIndex Container").first;
char_allocator alloc_inst(segment.get_allocator<char>());
shm_string key_object(alloc_inst);
key_object = "ST0012345SMD10000456";
std::pair<tag_set::index<stn>::type::iterator, tag_set::index<stn>::type::iterator> values = es->get<stn>().equal_range(key_object);
while(values.first != values.second) {
std::cout << values.first->name << " -- " <<" ("<<values.first->stn<<","<<values.first->mtype<<")\n";
++values.first;
}
char_allocator alloc_inst2(segment.get_allocator<char>());
shm_string key_object2(alloc_inst2);
key_object2 = "ST0012345SMD10000456.VoltsA";
///// is there any way something like the following can be done rather than the above iterator ?????
iterator it = values->get<name>(key_object2); <------- ????????????????????????
}
catch(const std::exception &exc){
std::cerr << "Exception caught: " << exc.what();
throw;
}
Sleep(3000);
return 0;
}
