Thread: Multithreading help

Hi All

I want to write a multithreaded program where I want to print string using 2 threads. ie. if String is:

Code:

char  a[] = {"Welcome to the world of Multithreading Programming"};

Thread 1: Welcome
Thread 2: To
Thread 1:The
Thread 2: World
and so on.

I used condition variable to preform this but not working fine.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

pthread_mutex_t count_mutex     = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  condition_var   = PTHREAD_COND_INITIALIZER;

void *functionCount1();
void *functionCount2();
int  count = 0;

main()
{
    char  a[] = {"Welcome to the world of Multithreading Programming"};
    int i = 0,rc ;
   pthread_t thread1, thread2;
   
   rc = pthread_create( &thread1, NULL, &functionCount1, a);
   pthread_create( &thread2, NULL, &functionCount2, a);
   pthread_join( thread1, NULL);
   pthread_join( thread2, NULL);

   exit(0);
}

void *functionCount1(char *a)
{
  
   for(;;)
   {  
      pthread_mutex_lock( &count_mutex );
      pthread_cond_wait( &condition_var, &count_mutex );
      while (a[count] != ' ' && a[count] != '\0')
      {
          printf("%c",a[count]);
          count++;
      }
      
      pthread_mutex_unlock( &count_mutex );

      if(a[count] == '\0') return(NULL);
    }
}

void *functionCount2(char *a)
{
    for(;;)
    {
       pthread_mutex_lock( &count_mutex );
       while (a[count] != ' ' && a[count] != '\0')
      {
          printf("%c",a[count]);
          count++;
      }
      pthread_cond_signal( &condition_var );
      pthread_mutex_unlock( &count_mutex );

       if(a[count] == '\0') return(NULL);
    }

}

When I run this code, nothing is happening.
The same thing I have used for printing numbers in alternate seq. and it works fine.

Can any suggest problem with the above code.

Thanks

Well, the first problem might be that your for(; loops would never terminate.

Code:

if(a[count] == '\0') return(NULL);

Should probably be

Code:

if(a[count] == '\0' || a[count] == ' ') return(NULL);

But another problem might be that you're doing this comparison after unlocking the mutex. Maybe make a copy of a[count] before unlocking and using that in the comparison. Also consider using isspace() (<ctype.h>) instead of comparing to ' '

I have done the same but it print

Welcome Welcome

and terminate. Is there any issue with using conditional variable.

Thanks oogabooga.
So you mean using one thread. But I want to do this using 2 threads.

Thanks

here is my code.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

pthread_mutex_t count_mutex     = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  condition_var   = PTHREAD_COND_INITIALIZER;

void *functionCount1();
void *functionCount2();
int  count = 0;


main()
{
    char  a[] = {"Welcome to the world of Multithreading Programming"};
    int i = 0,rc ;
   pthread_t thread1, thread2;
   
   rc = pthread_create( &thread1, NULL, &functionCount1, a);
   pthread_create( &thread2, NULL, &functionCount2, a);
  
   

   pthread_join( thread1, NULL);
   pthread_join( thread2, NULL);

   exit(0);
}

void *functionCount1(char *a)
{
  int temp = 0;
   for(;;)
   {  
      temp = count;
      pthread_mutex_lock( &count_mutex );
      pthread_cond_wait( &condition_var, &count_mutex );
      while (a[temp] != ' ' && a[temp] != '\0')
      {
          printf("%c",a[temp]);
          temp++;
      }
      
      pthread_mutex_unlock( &count_mutex );
      count = temp; 
      
      if(a[count] == '\0' ) return (NULL);
    }
}

void *functionCount2(char *a)
{
    int temp = 0;
    for(;;)
    {
       temp = count;
       printf("\nIn F2 %d %d",temp,count); 
       printf("\n");
       pthread_mutex_lock( &count_mutex );
       while (a[temp] != ' ' && a[temp] != '\0')
      {
          printf("%c",a[temp]);
          temp++;
      }
         count = temp;     
         pthread_cond_signal( &condition_var );
         pthread_mutex_unlock( &count_mutex );
      
      
     count = temp;        
     if(a[count] == '\0' ) return(NULL);
    }

}

Originally Posted by oogabooga

And I think SirPrattlepod is a little confused. There's nothing wrong with your loop. It's the way you're handling the condition_var.

I'm not confused at all

Code:

    for(;;)                                       // do "forever"

    {

       pthread_mutex_lock( &count_mutex );
       while (a[count] != ' ' && a[count] != '\0') // Let's assume a ' ' character ends the while loop

      {

          printf("%c",a[count]);
          count++;

      }

      pthread_cond_signal( &condition_var );

      pthread_mutex_unlock( &count_mutex );

 

       if(a[count] == '\0') return(NULL);              // We get to here, and a[count] == ' ', so this won't terminate the outer for loop...
                                                                                // I.e. how can the for loop ever end?

    }

can you please post the code here so I can check what need's to correct?

Thanks

ok..thats fine. It's yours.

Ok so you mean to say, that I should not use conditional variable and both thread use same function.
I tried this but this too not working.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

pthread_mutex_t count_mutex     = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  condition_var   = PTHREAD_COND_INITIALIZER;

void *functionCount1();
void *functionCount2();
int  count = 0;


main()
{
    char  a[] = {"Welcome to the world of Multithreading Programming"};
    int i = 0,rc ;
   pthread_t thread1, thread2;
   
   pthread_create( &thread1, NULL, &functionCount1, a);
   pthread_create( &thread2, NULL, &functionCount1, a);
  
   pthread_join( thread1, NULL);
   pthread_join( thread2, NULL);

   exit(0);
}

void *functionCount1(char *a)
{
   for(;;)
   {  
      
      pthread_mutex_lock( &count_mutex );
      //pthread_cond_wait( &condition_var, &count_mutex );
      while (a[count] != ' ' && a[count] != '\0')
      {
          printf("%c",a[count]);
          count++;
      }
      
      pthread_mutex_unlock( &count_mutex );
      
      if(a[count] == '\0') return (NULL);
    }
}