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up vote 1 down vote favorite

I have a requirement for creating a Event based Multi-thread application for which i am trying to use boost::thread and boost/interprocess/ipc/message_queue for sending messages between threads. What i am doing currently is making the thread wait in its workerfunction to wait for a message. Actually this is just for basic start where the sender and reciever both is a same thread, on later stage i have thought to store a list of message_queue corresponding for each thread and then fetch it accordingly or something like that. But now, as per the code below i am using

//in a common class

typedef struct s_Request{
int id;
}st_Request;


//in thread(XYZ) class
st_Request dataone;
message_queue *mq;

void XYZ::threadfunc(void *ptr)
{

  XYZ*obj = (XYZ*) ptr;
  obj->RecieveMsg();

}

void XYZ::RecieveMsg()
{
  message_queue mq1(open_only,"message_queue");
  if(!(mq1.try_receive(&dataone, sizeof(st_Request), recvd_size, priority)))
  printf("msg not recieved");

  printf("id = %d",dataone.id);
}
void XYZ::Create()
{
  mq= new message_queue(open_or_create,"message_queue",100,sizeof(st_Request));
  boost:thread workerthread(threadfunc,this);
  workerthread.join();
}

void XYZ::Send(st_Request *data)
{

  if (!(mq->try_send(data, sizeof(st_Request), 0)))
  printf("message sending failed");

}

//I am calling it like
class ABC: public XYZ
{
 ..some functions to do stuff... };
void ABC::createMSGQ()
{
  create();
  st_Request *data;
  data->id =10;
  send(data);
}

My thread is waiting in RecieveMsg but i am not getting any msg and the prints are coming till Send function entry and than the code crash. Please Guide me for what i am doing wrong, if the approach is entirely wrong, i am open to move to new approach.

P.s. this is my first question on stack overflow i tried follow the guidelines still if i strayed away anywhere please do correct.

share|improve this question
    
You should indent the code properly so it is readable. You can paste code in then highlight it and use Ctrl-K (or the {} icon) to indent the whole block consistently. Anyway, what is threadfunc? Why do you pass the argument to XYZ::ThreadFunc as void* instead of XYZ*? – Jonathan Wakely Sep 11 '14 at 14:35
    
@JonathanWakely - ThreadFunc is the Function from where the workerthread created starts its execution on being created. from here - boost:thread workerthread(threadfunc,this). And to be honest void * , was just passed following an example and later i cast it to XYZ* to access other member functions as ThreadFunc is a static member function. – Devansh Sep 11 '14 at 14:42
    
I didn't ask what ThreadFunc is, I asked what threadfunc is, which you use in Create. In C++ threadfunc is not the same as ThreadFunc. Please don't ask questions with nonsense code, it wastes everyone's time. Paste code that actually compiles or the question will get closed. – Jonathan Wakely Sep 11 '14 at 14:45
    
@JonathanWakely my bad. – Devansh Sep 11 '14 at 14:47

1 Answer 1

up vote 1 down vote 
st_Request *data;
data->id =10;

data is uninitialized, you cannot dereference it. Pointers should point to something before you dereference them.

I don't understand the point of this function:

void XYZ::Create()
{
  mq= new message_queue(open_or_create,"message_queue",100,sizeof(st_Request));
  boost:thread workerthread(threadfunc,this);
  workerthread.join();
}

You create a new thread, then block and wait for it to finish so you can join it. Why not just do the work here, instead of creating a new thread and waiting for it to finish?

What is threadfunc? Do you mean ThreadFunc?

This function is written strangely:

void XYZ::ThreadFunc(void *ptr)
{
  XYZ*obj = (XYZ*) ptr;
  obj->RecieveMsg();
}

Why not pass the argument as XYZ* instead of void*? Boost.Thread doesn't require everything to be passed as void*. Is that function static? It doesn't need to be:

struct XYZ {
  void threadFunc();
  void create();
  void recv();
};

void XYZ::threadFunc()
{
  recv();
}

void XYZ::create()
{
  boost::thread thr(&XYZ::threadFunc, this);
  thr.join();
}
share|improve this answer
    
ThreadFunc is my bad. its threadfunc only. and in RecieveMsg actually i am trying to achieve is that a thread is always waiting for a message as soon as it receives it does some stuff its supposed to do. I am not so sure now wethear or not i am going on the right approach. – Devansh Sep 11 '14 at 14:52
    
Your approach makes no sense, for the reasons given above. Creating a new thread and joining it immediately is useless. – Jonathan Wakely Sep 11 '14 at 15:02
    
thanks for the input, i would work on the points you mentioned, and may get back with another clarified approach hopefully. – Devansh Sep 11 '14 at 15:04

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