Question

Write a C code to let the main thread create N child threads, where each created thread will randomly generate an integer between 0 to 10 and put it into a global array variable. After that, the main thread will calculate the sum of all the generated integers. N should be input as a command line argument.

Complete the following C code by filling all “???”s in the code sketch. NOTE: when you compile the code, you need to add the parameter “-lpthread” to “gcc”, e.g., “gcc YourCode.c -lpthread”

// include the header file that allows us to use pthread
#include <???>
#include <stdio.h>
// include the header file that allows us to use dynamic memory management 
#include <???>
// define a pointer to point to an array to hold the randomly generated integers
int *a;

// define the function used to create a thread
???runner(???param);

int main(int argc, char *argv[])
{
        if (argc != 2)
        {
                fprintf(stderr, "usage: %s <integer value>\n", argv[0]);
                return -1;
        }

        int N = atoi(argv[1]);

        if (N<=0)
        {
                fprintf(stderr, "%d must be > 0\n", N);
                return -1;
        } 

        // define an array to hold the threads to be created
        ???              workers[N]; 

        // define a set of thread attributes for creating threads
???                     attr;

        // define a variable later used for “for” loop
int i;

        // use dynamic memory management to create an array to hold the integers
        a = ???                                         ;

        // seed the random number generator
        srandom((unsigned)time(NULL));

        // initialize the default thread attributes
        ???





        // use “for” loop to create the threads, where the index of the created thread in workers
// array should be passed to the thread as the parameter
        ???





        // use “for” loop to wait for all the threads to exit
        ???




        // calculate the sum
        int sum = 0;

        for (i=0; i<N; i++) sum += a[i];

        printf("sum = %d\n", sum);

        // free the dynamically created array
        ???

}

// The created thread will start its execution from this function
???             runner(???              param)
{
        // get the index of the thread in workers array and put it to “thread_index”
        int thread_index = ???                          ;       

        // randomly generate an integer between 0 to 10
        a[thread_index] = random()%11;  

        // print the information on the screen
        printf("Thread %d generates integer %d ...\n", thread_index, a[thread_index]);

        // terminate the thread
        ???



}

Answer 1

#include <pthread.h>
#include <stdio.h>
// include the header file that allows us to use dynamic memory management
#include <stdlib.h>
// define a pointer to point to an array to hold the randomly generated integers
int *a;

// define the function used to create a thread
void * runner(void* param);

int main(int argc, char *argv[])
{
if (argc != 2)
{
fprintf(stderr, "usage: %s <integer value>\n", argv[0]);
return -1;
}

int N = atoi(argv[1]);

if (N <= 0)
{
fprintf(stderr, "%d must be > 0\n", N);
return -1;
}

// define an array to hold the threads to be created
pthread_t workers[N];
  
void* rval;

// define a set of thread attributes for creating threads
pthread_attr_t attr;

// define a variable later used for “for” loop
int i;

// use dynamic memory management to create an array to hold the integers
a = (int*)calloc(N, sizeof(int)); ;

// seed the random number generator
srandom((unsigned)time(NULL));

// initialize the default thread attributes
pthread_attr_init(&attr);

// use “for” loop to create the threads, where the index of the created thread in workers
// array should be passed to the thread as the parameter
for(i=0;i<N;i++) {
pthread_create(&workers[i],&attr,runner,i);
}

// use “for” loop to wait for all the threads to exit
for(i = 0; i < N; i++)
pthread_join(workers[i],&rval);

// calculate the sum
int sum = 0;

for (i=0; i<N; i++) sum += a[i];

printf("sum = %d\n", sum);

// free the dynamically created array
free(a);

}

// The created thread will start its execution from this function
void* runner(void* param)
{
// get the index of the thread in workers array and put it to “thread_index”
int thread_index = (int *)param; ;   

// randomly generate an integer between 0 to 10
a[thread_index] = random()%11;

// print the information on the screen
printf("Thread %d generates integer %d ...\n", thread_index, a[thread_index]);

// terminate the thread
pthread_exit(NULL);
}

OUTPUT :

For N = 10