Multithread in C++

Asuralm · 11-07-2008, 11:26 AM

Hi all:

I have a function

void FuncA(obj o, arg1 a1, arg2 a2);

Because I have to run the FuncA for many times for different objects, I am thinking it's probably better to run multithread so that each thread contains each object. I have just read a small tutorial in http://www.yolinux.com/TUTORIALS/Lin...ixThreads.html

However, I am still not sure how to start a thread if the arguments of FuncA is multiple.

Also, the pthread_t looks quite out-of-date and it's in C although it works in C++.

Could anyone give me any idea how to do this please?

Thanks

jf.argentino · 11-07-2008, 12:28 PM

Quote:

However, I am still not sure how to start a thread if the arguments of FuncA is multiple.

You can't you have to design a structure to embed all the arguments you want into one. For example:

Code:

struct obj;
struct arg1;
struct arg2;

struct ThreadArgs {
   obj* o;
   arg1* a1;
   arg2* a2;
};

void* start_FuncA (void* arg) {
   struct ThreadArgs my_args = (struct ThreadArgs*) arg;
   FuncA (*my_args->o, *my_args->a1, *my_args->a2);
   return NULL;
}

int main (void) {
   struct obj o;
   struct arg1 a1;
   struct arg2 a2;
   struct ThreadArgs args;
   pthread_t thread;
   
   args.o = &o;
   args.a1 = &a1;
   args.a2 = &a2;
   pthread_create (&thread, NULL, start_FuncA, &args);
   /* ... */
   return 0;
}

Quote:

Also, the pthread_t looks quite out-of-date

pthread stand for Posix Thread, it's an interface definition to interact with a POSIX compliant system.... So the implementation you're using can be outdated if you're running an old system, but the interface isn't, or if it's the case it means that POSIX itself is outdated, and as far as I know, it's not the case...

Quote:

it's in C although it works in C++.

pthread implementation is wrotten in C, as all system relative tasks: read, write, ioctl, socket... because C _IS_ the UNIX native language... If you want something that is more "C++" look_and-feel, you have to find a wrapper, but if you take a look inside the wrapper code, you'll see call to the same C functions. But it isn't a silly question, if you want to use a wrapper, choose a good library, many are portable, that means that you will be able to compile the same code under POSIX (all UNICES) and non-POSIX (windows and ???), because the library replace the pthread_XXX functions with the one for non-POSIX system.

estabroo · 11-07-2008, 01:48 PM

I think c++ boost library has a threading class (that's probably a wrapper for pthread) http://www.boost.org and its available in most distributions directly just need to install it.

dwhitney67 · 11-08-2008, 10:55 PM

Define your objects to be the thread. Basically, you need to define your objects to be functor-objects; then you can use Boost or a variation of such (perhaps a creation of your own?).

For example, with Boost:

PHP Code:



#include <boost/thread/thread.hpp> 
... 
 
class Object1 
{ 
  public: 
    // constructor 
    Object1(arg1 a1, arg2 a2) 
      : m_a1(a1), 
        m_a2(a2) 
    { 
    } 
 
    // thread process 
    void operator()(void) 
    { 
       // do something with m_a1 and m_a2 
    } 
 
  private: 
    arg1 m_a1; 
    arg2 m_a2; 
}; 
 
// repeat for other Object classes (e.g. Object2, Object3, ..., ObjectN) 
 
int main() 
{ 
  arg1 a1; 
  arg2 a2; 
 
  Object1 obj1(a1, a2); 
  Object2 obj2(a1, a2); 
  ... 
  ObjectN objN(a1, a2); 
 
  boost::thread_group threads; 
  threads.add_thread(new boost::thread(obj1)); 
  threads.add_thread(new boost::thread(obj2)); 
  ... 
  threads.add_thread(new boost::thread(objN)); 
 
  threads.join_all(); 
 
  return 0; 
}

Of course, in the example above, all Objects are using the same arg1 and arg2 objects. This probably will not be the case for your application.

sundialsvcs · 11-10-2008, 10:01 AM

Multithreading does not multiply the computer's time and capabilities, but rather, divides it.

My instincts tell me that, if your task is highly resource-intensive, it is very unlikely that multithreading will help matters. Finding a more-optimized algorithm is much more likely to bring success.