Question

Read given code RaceOrNot1.c and write all possible outputs of the program. Assume there will be no thread creation or joining failures or mutex failures. If you believe there is only one possible output, you just need to write that output.

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

pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t count_mutex3 = PTHREAD_MUTEX_INITIALIZER;
int c[2] = {1,0};

void *UpdateC1(void *arg)
{
   int i;
   for(i=0;i<1000000;i++)
   {
       pthread_mutex_lock(&count_mutex);
       c[0]=(c[0]+1)%2;
       c[1]=(c[1]+1)%2;
       pthread_mutex_unlock(&count_mutex);
   }
   return NULL;
}

void *UpdateC2(void *arg)
{
   int i;
   for(i=0;i<2000000;i++)
   {
       pthread_mutex_lock(&count_mutex);
       c[0]=(c[0]+1)%2;
       c[1]=(c[1]+1)%2;
       pthread_mutex_unlock(&count_mutex);
   }
   return NULL;
}

void *UpdateC3(void *arg)
{
   int i;
   for(i=0;i<3000000;i++)
   {
       pthread_mutex_lock(&count_mutex3);
       c[0]=(c[0]+1)%2;
       c[1]=(c[1]+1)%2;
       pthread_mutex_unlock(&count_mutex3);
   }
   return NULL;
}

int main(int argc, char *argv[])
{
   int rt,i;
   pthread_t t[3];

   rt=pthread_create( &t[0], NULL, &UpdateC1, NULL);
   if( rt!=0 )
       fprintf(stderr,"Thread %d creation failed: %d\n", 0,rt);
   rt=pthread_create( &t[1], NULL, &UpdateC2, NULL);
   if( rt!=0 )
       fprintf(stderr,"Thread %d creation failed: %d\n", 1,rt);
   rt=pthread_create( &t[2], NULL, &UpdateC3, NULL);
   if( rt!=0 )
       fprintf(stderr,"Thread %d creation failed: %d\n", 2,rt);

   for(i=0;i<3;i++)
   {
       rt=pthread_join( t[i], NULL);
       if( rt!=0 )
           fprintf(stderr,"Wait for thread %d failed: %d\n", i,rt);
   }

   printf ("\t%c\t%c\n",'a'+c[0],'a'+c[1]);
   return 0;
}

Answer 1

Tweet Share 0 Success #include<stdio.h> 1 #include <stdlib.h> 2 #include <pthread.h> 3 4 5 pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZER; pthread_mutex_t count_mutex3 PTHREAD_MUTEX_INITIALIZER; int c[2] 1,0; 7 = 8 void *UpdateC1 (void *arg) 10- int i; 11 for(i=0;i<1000000; i++) 12 13 pthread_mutex_lock(&count_mutex); c[]=(c[®]+1)%2; c[1] (c[1]+1)%2; pthread_mutex_unlock (&count_mutex) ; 14 15 16 17 18 19 return NULL; 20 } 11 Run (Ctri-Enter) (0.17 sec) Output Input Comments Text a a NmtunoN

Tweet Share 0 Success #include <stdio.h 1 #include<stdlib.h> 2 #include <pthread. h> 4 5 pthread_mutex_t count_mutex = PTHREAD_MUT EX_INITIALIZER; pthread_mutex t count mutex3 int c[2] PTHREAD_MUTEX_INITIALIZER ; 6 - {1,0); 7 void *UpdateCi (void *arg) 10- int i; for(i-0;i<1000000 ; i++) 11 12 13 pthread_mutex_lock(&count_mutex); c[]=(c[®]+1)%2; c[1]=(c[1]+1)%2; pthread_mutex_unlock (&count_mutex); } return NULL; 14 15 16 17 18 19 20 21 Run (Ctri-Enter) (0.15 sec) Output Input Comments0 Text b C

Tweet Share 0 Success #include <stdio.h> 1 #include <stdlib.h> 2 #include <pthread.h> 4 pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZ ER ; 5 pthread_mutex_t count_mutex3 = PTHREAD_MUTEX_INITIALIZER; 6 int c[2] 7 {1,0}; 8 void UpdateC1(void arg) 9 10 int i for(i=0;i<1000000; i++) 11 12 13 pthread_mutex_lock(&count_mutex) ; c[]=(c[®]+1)%2; c[1]=(c[1]+1)%2; pthread_mutex_unlock (&count_mutex) ; 14 15 16 17 18 19 return NULL; 20 11 Run (Ctri-Enter) Output Input Comments (0.15 sec Text b a

Possible outputs are:

a a

a b

b a

exaplaination:

at any time one thread will be running as there is a mutex lock wheneven there is a updation in each thread execution. So 3 possible values for the array of C are (0,0) , (0,1) , (1,0)

After the all theards completes their execution , there is printf which prints the a character

a + c[0] a+c[1] ie a + 0 a+ 0=> a a

a + c[0] a+c[1] ie a +0 , a+1 => a b

a + c[0] a+c[1] ie a +1 a+0 => b a