CODEWITHSUNDEEP
c++multithreadingpthreads
Manish
Manish

Reputation: 3531

Example for multithreadig in C++

Currenly i am working on one example in which i am using multireading in C++. 

#include <iostream>
#include <cstdlib>
#include <pthread.h>

using namespace std;

#define NUM_THREADS     2

void *PrintHello(void *threadid) 
{
     long tid;
     tid = (long)threadid;
     for (int i =0; i < 20000000000; i++)
     {
        int x;
        x=x+x*x;
     }
     cout << "Hello World! Thread ID, " << tid << endl;
     pthread_exit(NULL);
 }

 int main ()
 {
     pthread_t threads[NUM_THREADS];
     int rc;
     int i;
     for( i=0; i < NUM_THREADS; i++ ){
        cout << "main() : creating thread, " << i << endl;
     rc = pthread_create(&threads[i], NULL, 
                      PrintHello, (void *)i);
     if (rc){
         cout << "Error:unable to create thread," << rc << endl;
         exit(-1);
     }
  }
  pthread_exit(NULL);
}

But as number of cores on my pc is 2 so i am supposed to get 2 threads while using top. 

  ./multithreadprogram 
   main() : creating thread, 0
   main() : creating thread, 1

But on top i see only one 

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND                                                                                                           
  13316 manish    20   0     0    0    0 Z 196.6  0.0   0:16.95 multithreadprog                                                                                                   
  3629 manish    20   0  528m  25m  12m S   0.7  0.3   0:32.57 gnome-terminal

As far as i know i should be able to get 2 threds running parallely on top. Pls help me out as i am newbie to multithreading.

Upvotes: 0

Views: 81

Answers (1)

Яois
Яois

Reputation: 3858

Notice the 196% CPU in the process table, it means your program is running in more than one core ;)

Upvotes: 1

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