Btukfyl

This is my first attempt at using a mutex with parallel processing to try to make the results come out correctly. I have a simple program which computes the first 25 Fibonacci numbers in parallel threads. When I have the create and join in the same for loop the results are correct. When I put the join in a second for loop this is the output:

Thread[0] created   Thread[1] created   The fibonacci of 2= -1073741824

Thread[2] created   The fibonacci of 2= -1073741824

Thread[3] created   The fibonacci of 3= -2147483648

The fibonacci of 4= 1073741824

Thread[4] created   The fibonacci of 4= 1073741824

Thread[5] created   The fibonacci of 5= -1073741824

Thread[6] created   The fibonacci of 7= 455617800

Thread[7] created   The fibonacci of 8= 1984977424

Thread[8] created   The fibonacci of 8= 1984977424

Thread[9] created   The fibonacci of 10= 1985010191

Thread[10] created  The fibonacci of 11= 1985042958

Thread[11] created  The fibonacci of 11= 1985042958

Thread[12] created  The fibonacci of 12= -324914147

Thread[13] created  The fibonacci of 13= 1660128811

Thread[14] created  The fibonacci of 15= 1660128811

Thread[15] created  The fibonacci of 16= 1660128811

Thread[16] created  The fibonacci of 16= 1660128811

Thread[17] created  The fibonacci of 18= 1660128811

Thread[18] created  The fibonacci of 19= 1660128811

Thread[19] created  The fibonacci of 20= -974709674

Thread[20] created  The fibonacci of 20= -974709674

Thread[21] created  The fibonacci of 22= -974709674

Thread[22] created  The fibonacci of 23= -974709674

Thread[23] created  The fibonacci of 23= -974709674

The fibonacci of 24= -1949419348

Thread[24] created  Thread[0] joined & exited

Thread[1] joined & exited

Thread[2] joined & exited

Thread[3] joined & exited

Thread[4] joined & exited

Thread[5] joined & exited

Thread[6] joined & exited

Thread[7] joined & exited

Thread[8] joined & exited

Thread[9] joined & exited

Thread[10] joined & exited

Thread[11] joined & exited

Thread[12] joined & exited

Thread[13] joined & exited

Thread[14] joined & exited

Thread[15] joined & exited

Thread[16] joined & exited

Thread[17] joined & exited

Thread[18] joined & exited

Thread[19] joined & exited

Thread[20] joined & exited

Thread[21] joined & exited

Thread[22] joined & exited

Thread[23] joined & exited

Thread[24] joined & exited

Can you tell me why the mutex isn't keeping the threads processing in the correct order? Here is the program:

#include<stdio.h> //for printf

#include<stdlib.h>  //for malloc

#include<pthread.h> //for threading



#define SIZE 25 //number of fibonaccis to be computed

int *fibResults;  //array to store fibonacci results

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;



//function takes the index for fibResults as a void pointer

//assigns it to an int variable, calculates and prints

//the results of the fibonacci calculations

void *run(void *ptrarg)  //executes and exits each thread

{

  pthread_mutex_lock (&mutex1);

  int arg = *((int *)ptrarg);

  if (arg == 0)

  {

    fibResults[arg] = 0;

    printf("The fibonacci of %d= %dn", arg, fibResults[arg]);    

    pthread_mutex_unlock (&mutex1); 

    pthread_exit(0); 

  }



  else if (arg == 1)

  {

    fibResults[arg] = 1;

    printf("The fibonacci of %d= %dn", arg, fibResults[arg]);   

    pthread_mutex_unlock (&mutex1);   

    pthread_exit(0);  

  }

  else

  {

    fibResults[arg] = fibResults[arg -1] + fibResults[arg -2];

    printf("The fibonacci of %d= %dn", arg, fibResults[arg]);

    pthread_mutex_unlock (&mutex1);

    pthread_exit(0);

  }

}



//main function that drives the program.

//Loops through created and joining threads

//passes the index value of the fib array

//to the thread run function

int main()

{

  pthread_attr_t a;

  fibResults = (int*)malloc (SIZE * sizeof(int));

  pthread_attr_init(&a);  

  pthread_t thread_id[SIZE];  



  for (int i = 0; i < SIZE; i++)

  {

    pthread_t thread;

    pthread_create(&thread_id[i], &a, run,(void*) &i);

    printf("Thread[%d] createdt", i); 

    fflush(stdout);

  }



  for (int j = 0; j < SIZE; j++)

  {

    pthread_join(thread_id[j], NULL);

    printf("Thread[%d] joined & exitedn", j); 

  }

  return 0;

}