Re: [Boost-users] managed shared memory with basic_string

Subject: Re: [Boost-users] managed shared memory with basic_string
From: Sean K (sk92129_at_[hidden])
Date: 2014-03-07 15:52:47

I figured it out.

In the reader, I was using the wrong basic_string.

by accident, I was using the std::basic_string.   I should have been using
boost::interprocess::basic_string.

I changed that.  Then it worked.

On Fri, Mar 7, 2014 at 12:37 PM, Sean K <sk92129_at_[hidden]> wrote:

> I am new to boost so please pardon if this question has already been asked.
>
> I was able to build a shared memory IPC client and server using "int"
> primitive type successfully.
>
> I need to send a fixed number of "char" (primitive type).   At first I
> tried to define a struct of a fixed char
>
> struct {
>       char data[1024];
> } dataset;
>
> typedef dataset mychararray;
>
> and use this like how this example shows for 'int"
>
>
> http://en.highscore.de/cpp/boost/interprocesscommunication.html#interprocesscommunication_managed_shared_memory
>
> But for some reason it did not compile due to the boost::interprocess::managed_shared_memory.construct
> () not accepting that kind of datatype.
>
> So, I looked at the basic_string implementation based on these two web
> sites.
> http://prakharprakhar.blogspot.com/2009/12/boost-shared-memory-vector.html
>
> http://en.highscore.de/cpp/boost/interprocesscommunication.html#interprocesscommunication_managed_shared_memory (basic_string
> variant)
>
> I am built a reader and writer separate app. The reader will look for
> content.   If it does not find it, it will wait or sleep and try again,
> etc.   If it finds something it will try to print the basic_string content
> that I sent over.
>
> I thought I had it correctly built but obviously it is not since the
> reader server crashes or cores when it tries to access the p.first content.
>
>
> Below are the two programs (along with the build.sh which compiles each).
>  I am testing this as a 32 bit app  on a 64 bit redhat5 and 32 bit centos6.
>
>
>
> You  will notice in the strreader.cc that when I try to access the
> basic_string, that it crashes.
>
> I ran the reader (server) within the 32 bit eclipse debugger, and the
> memory addresses and content of the p BStringPair looks fine.   Anybody
> have some ideas or can anybody try this and see what you can tell what is
> wrong.
>
> strreader.cc
>
>
>
> #include <iostream>
>
>
>
> #include <boost/interprocess/managed_shared_memory.hpp>
> #include <boost/thread/thread.hpp>
> #include <boost/interprocess/containers/vector.hpp>
> #include <boost/interprocess/allocators/allocator.hpp>
>
> #include <iostream>
> #include <string>
> #include <cstdlib>
>
> using namespace std;
> using namespace boost::interprocess;
>
>
> int main() {
>
> typedef boost::interprocess::allocator<char,
> boost::interprocess::managed_shared_memory::segment_manager> ShmemAllocator;
>  typedef basic_string<char, std::char_traits<char>, ShmemAllocator>
> BString;
>
> typedef std::pair<BString *, std::size_t> BStringPair;
>
> int count = 0;
> shared_memory_object::remove("Highscore");
> while (true) {
>  managed_shared_memory segment(open_or_create, "Highscore", 65536);
>
> if (segment.get_num_named_objects() > 0){
>  BStringPair p = segment.find<BString> ("str");
> printf("stuff in memory\n");
>
>  if (p.first ){
>
>                                 // THIS IS WHERE IT CRASHES!!!
> //printf("%s \n",(p.first->c_str()) );
>  //int strlen = p.first->size();
> }
> printf("p.second: %d \n", p.second);
>  }
>
> shared_memory_object::remove("Highscore");
> //printf("one: %s", one.first);
>  //printf("two: %s", two.first);
>
>     int msecs = 2000;
> boost::this_thread::sleep(boost::posix_time::milliseconds(msecs));
>  printf("sleeping...\n");
>     }
>
>
> return 0;
> }
>
>
> build.sh for the reader
>
> g++ -m32 -fPIC -Xlinker -zmuldefs  strreader.cc -o strreader
> -I/common/COTS/boost_1_42_0/include -L/common/COTS/boost_1_42_0/lib
> -lboost_thread -lboost_system -pthread
>
>
> strwriter.cpp
>
>
> #include <iostream>
>
>
>
> #include <boost/interprocess/managed_shared_memory.hpp>
> #include <boost/thread/thread.hpp>
> #include <boost/interprocess/containers/vector.hpp>
> #include <boost/interprocess/containers/string.hpp>
> #include <boost/interprocess/allocators/allocator.hpp>
>
> #include <iostream>
> #include <string>
> #include <cstdlib>
>
>
> using namespace std;
> using namespace boost::interprocess;
>
>
> int main() {
>
> typedef boost::interprocess::allocator<char,
> boost::interprocess::managed_shared_memory::segment_manager> ShmemAllocator;
>  typedef boost::interprocess::basic_string<char, std::char_traits<char>,
> ShmemAllocator> BString;
>
>
> try {
>  shared_memory_object::remove("Highscore");
> printf("cleared out memory\n");
>
>
> managed_shared_memory segment(open_or_create, "Highscore", 65536);
>
> printf("initialized managed shared memory \n");
>  ShmemAllocator allocInst (segment.get_segment_manager());
> BString bstrData(segment.get_segment_manager());
>  bstrData = "hello";
>
> std::string data = "Hello";
> //BString bstrToSend(data.begin(), data.end());
> //BString bstrToSend(data.c_str());
>
> BString *mystring = segment.construct<BString> ("str")(bstrData);
>
> //mystring="Hello";
>
> printf("inserted mystring into shmvector \n");
> } catch (boost::interprocess::bad_alloc e) {
>  printf("we caught bad alloc\n");
> printf("explanation: %s", e.what());
> throw;
>  } catch (...) {
> printf("caught unknown exception\n");
> throw;
>  }
>
> printf("wrote number");
> return 0;
>  }
>
>
> build.sh for the writer:
> g++ -m32 -fPIC -Xlinker -zmuldefs  strwriter.cpp -o strwriter
> -I/common/COTS/boost_1_42_0/include -L/common/COTS/boost_1_42_0/lib
> -lboost_thread -lboost_system -pthread
>
> --
> Sean
>

-- 
Sean