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POboost::multi_index_container - equal_range values
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  1. POboost::multi_index_container - equal_range values
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    copied!<p>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).</p> <p>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.</p> <p>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.</p> <p>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).</p> <p>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).</p> <p>Below is the code for my program which is retrieving items from a seperate process that created the multi_index_container.</p> <pre><code>using namespace boost::interprocess; using namespace System; namespace bmi = boost::multi_index; typedef managed_shared_memory::allocator&lt;char&gt;::type char_allocator; typedef basic_string&lt;char, std::char_traits&lt;char&gt;, char_allocator&gt;shm_string; struct tag { shm_string name; shm_string stn; shm_string mtype; int id; tag( const char *name_ , const char_allocator &amp;a , const char *stn_ , const char_allocator &amp;b , const char *mtype_ , const char_allocator &amp;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&lt; tag, bmi::indexed_by&lt; bmi::ordered_unique &lt;bmi::tag&lt;name&gt;, BOOST_MULTI_INDEX_MEMBER(tag,shm_string,name)&gt;, bmi::ordered_non_unique&lt; bmi::tag&lt;stn&gt;,BOOST_MULTI_INDEX_MEMBER(tag,shm_string,stn)&gt; &gt;, managed_shared_memory::allocator&lt;tag&gt;::type &gt; tag_set; typedef tag_set::iterator iterator; int main(array&lt;System::String ^&gt; ^args) { try{ managed_shared_memory segment(open_only,"MySharedMemory"); offset_ptr&lt;tag_set&gt; es = segment.find&lt;tag_set&gt;("My MultiIndex Container").first; char_allocator alloc_inst(segment.get_allocator&lt;char&gt;()); shm_string key_object(alloc_inst); key_object = "ST0012345SMD10000456"; std::pair&lt;tag_set::index&lt;stn&gt;::type::iterator, tag_set::index&lt;stn&gt;::type::iterator&gt; values = es-&gt;get&lt;stn&gt;().equal_range(key_object); while(values.first != values.second) { std::cout &lt;&lt; values.first-&gt;name &lt;&lt; " -- " &lt;&lt;" ("&lt;&lt;values.first-&gt;stn&lt;&lt;","&lt;&lt;values.first-&gt;mtype&lt;&lt;")\n"; ++values.first; } char_allocator alloc_inst2(segment.get_allocator&lt;char&gt;()); 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-&gt;get&lt;name&gt;(key_object2); &lt;------- ???????????????????????? } catch(const std::exception &amp;exc){ std::cerr &lt;&lt; "Exception caught: " &lt;&lt; exc.what(); throw; } Sleep(3000); return 0; </code></pre> <p>}</p>
 

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