[Boost-users] Help with custom classes PLEASE!!

[Daniel Veneros]

Hi, I am trying to create a shared memory segment where I can share a STRING between 2 process, I tried using the following code:

In the "main" process:

#include <boost/interprocess/managed_shared_memory.hpp>

#include <boost/interprocess/containers/vector.hpp>

#include <boost/interprocess/allocators/allocator.hpp>

#include <cstdlib>

#include <string>

#include <iostream>

using namespace boost::interprocess;

typedef allocator<std::string, managed_shared_memory::segment_manager> ShMemAllocator;

typedef vector<std::string, ShMemAllocator> MyVector;

int main(int argc, char** argv) {

    struct shm_remove {

        shm_remove() {shared_memory_object::remove("MySharedMemory"); }

        ~shm_remove() {shared_memory_object::remove("MySharedMemory"); }

    }remover;

    managed_shared_memory segment(create_only, "MySharedMemory", 65536);

    const ShMemAllocator alloc_inst(segment.get_segment_manager());

    MyVector *myVector = segment.construct<MyVector>("MyVector")(alloc_inst);

        myVector->push_back("a");

    int stop; //this line helps me wait until i run the other process

    std::cin >> stop;

    return (EXIT_SUCCESS);

}

at the "client" process:

#include <boost/interprocess/managed_shared_memory.hpp>

#include <boost/interprocess/containers/vector.hpp>

#include <boost/interprocess/allocators/allocator.hpp>

#include <cstdlib>

#include <string>

#include <iostream>

using namespace boost::interprocess;

typedef allocator<std::string, managed_shared_memory::segment_manager> ShMemAllocator;

typedef vector<std::string, ShMemAllocator> MyVector;

int main(int argc, char** argv) {

    managed_shared_memory segment(open_only, "MySharedMemory");

    MyVector *myVector = segment.find<MyVector>("MyVector").first;

     std::cout << "myVector size: " << myVector->at(0) << std::endl;   

    return (EXIT_SUCCESS);

}

When I run both I receive an error "Segmentation Fault, Core Dumped"...

Does anyone know how to solve this?

Thanks

Dann

[Steven Watanabe]

AMDG

Daniel Veneros wrote:
> Hi, I am trying to create a shared memory segment where I can share a STRING
> between 2 process, I tried using the following code:
>

> *In the "main" process:*

>
> #include <boost/interprocess/managed_shared_memory.hpp>
> #include <boost/interprocess/containers/vector.hpp>
> #include <boost/interprocess/allocators/allocator.hpp>
> #include <cstdlib>
> #include <string>
> #include <iostream>
>
>
> using namespace boost::interprocess;
>
>
> typedef allocator<std::string, managed_shared_memory::segment_manager>
> ShMemAllocator;
>
> typedef vector<std::string, ShMemAllocator> MyVector;
>

You can't use std::string. You need to use
boost::interprocess::basic_string
with an appropriate allocator (just as you need to use
boost::interprocess::vector
instead of std::vector).

In Christ,
Steven Watanabe

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[Daniel Veneros]

Hi,

Thanks, this works now...

I got one othr question, what if I want to share a MAP type between both processes? a map that has a string as a key and a custom class as a value?

I mean:

class Employee {

private: 

string name;

int age;

public:

Employee();

~Employee();

};

map<string, Employee>

Somehing like that... how can I implement that? I tried doing this:

using namespace boost::interprocess;

map<std::string, Employee> myMap;

typedef allocator<myMap, managed_shared_memory::segment_manager> ShMemAllocator;

typedef vector<myMap, ShMemAllocator> MyVector;

But it's not working...

THANKS!!!

Dann

[Steven Watanabe]

AMDG

Daniel Veneros wrote:
> I got one othr question, what if I want to share a MAP type between both
> processes? a map that has a string as a key and a custom class as a value?
>

The map and the string both need to have allocators.

[Daniel Veneros]

And what about the class?

Do i just need to  create allocators for the map and the string(the map's key)??

     typedef allocator<basic_string, managed_shared_memory::segment_manager>StrAllocator;

typedef Employee Value;

typedef std::pair<StrAllocator, Employee> ValueType;

typedef allocator<ValueType, managed_shared_memory::segment_manager>ShMemAllocator; typedef map<StrAllocator, Value, std::less<StrAllocator>, ShMemAllocator> MyMap;

Is this correct?

Thank you very much again...

Dann

[Steven Watanabe]

AMDG

Daniel Veneros wrote:
> And what about the class?
>

Oh, I see.

> class Employee {
> private:
> string name;
> int age;
>
> public:
> Employee();
> ~Employee();
> };

The string inside the class needs to use an allocator too.

Everything that allocates memory which you store in
shared memory needs to use the right allocator.

[Steven Watanabe]

AMDG

Daniel Veneros wrote:
> Thanks,
>
> I fixed some things and its running now.
> What I don't know how to do is to declarate/allocate a custom class..
> I got this:
>
> typedef managed_shared_memory::segment_manager SegmentManager;
>
> typedef allocator<char, SegmentManager> CharAllocator;
>
> typedef basic_string<char, std::char_traits<char>, CharAllocator>
> BasicString;
>
> typedef allocator<int, SegmentManager> IntAllocator;
>
>
> class Action
> {
> int id;
> BasicString task;
> public:
> Action(int num, const char *name, const VoidAllocator &void_alloc)
> :id(num), task(name,void_alloc)
> {}
> void setId(int num);
> void setTask(BasicString newTask);
> };
>
> void Action::setId(int num) {
> id = num;
> }
>
> void Action::setTask(BasicString newTask) {
> task = newTask;
> }
>
>
> Now... how should I allocate the "Class" object??
> Any Idea? Thanks!!
>

I assume that by Class you mean the Action class?
If this class is used at the top level, you can use
managed_shared_memory::construct. If you want
to use an allocator with it, the commands are

allocator<Action, SegmentManager> alloc(...);
// allocate memory
Action* action = alloc.allocate(1);
// construct an object using placement new
new (action) Action(12, "action", ...);

In Christ,
Steven Watanabe

P.S. Please send messages like this to boost-users rather than directly
to me.

[Daniel Veneros]

Hi, thanks for all the help, everything is working perfect now.

I have another question, I need to access the shared memory segment from several process and all at the same time. I tried to use pthreads but that didn't work.

I was looking at boost::interprocess threads but I'm not sure how to implement the mutex.

this is the code I have:

#include <boost/interprocess/managed_shared_memory.hpp>

#include <boost/interprocess/containers/vector.hpp>

#include <boost/interprocess/containers/string.hpp>

#include <boost/interprocess/containers/map.hpp>

#include <boost/interprocess/allocators/allocator.hpp>

#include <cstdlib>

#include <string>

#include <iostream>

#include <map>

#include <sstream>

using namespace boost::interprocess;

typedef managed_shared_memory::segment_manager SegmentManager;

typedef allocator<void, SegmentManager> VoidAllocator;

typedef allocator<char, SegmentManager> CharAllocator;

typedef basic_string<char, std::char_traits<char>, CharAllocator> BasicString;

class Action

{

    int id;

    BasicString task;

public:

    Action(int num, const char *name, const VoidAllocator &void_alloc)

            :id(num), task(name,void_alloc)

            {}

            void setId(int num);

            void setTask(BasicString newTask);

            int getId();

};

int Action::getId() {

    return id;

}

void Action::setId(int num) {

    id = num;

}

void Action::setTask(BasicString newTask) {

    task = newTask;

}

typedef allocator<Action, SegmentManager> ActionAllocator;

typedef std::pair<const BasicString, Action> MapValueType;

typedef std::pair<BasicString, Action> MovableToMapValueType;

typedef allocator<MapValueType, SegmentManager> MapValueTypeAllocator;

typedef map<BasicString, Action, std::less<BasicString>, MapValueTypeAllocator> MyMap;

int main(int argc, char** argv) {

    //Remove shared memory on construction and destruction

    struct shm_remove {

        shm_remove() {shared_memory_object::remove("MySharedMemory"); }

        ~shm_remove() {shared_memory_object::remove("MySharedMemory"); }

    }remover;

    

    managed_shared_memory segment(create_only, "MySharedMemory", 65536);

    VoidAllocator alloc_inst(segment.get_segment_manager());

   MyMap *myMap = segment.construct<MyMap>("Map")(std::less<BasicString>(),alloc_inst);

    std::string keyword;

    std::string helper;

    int i=0;

    for(int adder = 0; adder<=1000; adder++)

    {

        keyword = "Hello";

        std::stringstream out;

        out << adder;

        helper = out.str();

        keyword = keyword + helper;//Creates a string "Hello" + adder

        BasicString key(keyword.c_str(), alloc_inst);//string to BasicString

        Action action(i,"Hello", alloc_inst);

        MapValueType value(key, action);

        myMap->insert(value);

        i++;

    }

        

How do I have to set the mutex??

Thanks!

Dann