How do we extend the program from 4 to 8 threads in C [closed] - c

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I have started learning C in Uni, and now I'm stuck on posix threads. I have a program that has a single thread, 2 threads and 4 threads as an example from lecture. I need your help to extend this program from 4 to 8/16/32 and how it will perform a difference or not?
Thank you in advance.
Here is the code for 4 thread programm:
/****************************************************************************
This program finds groups of three numbers that when multiplied together
equal 98931313. Compile with:
cc -o factorise4 factorise4.c -lrt -pthread
Kevan Buckley, University of Wolverhampton, October 2012
*****************************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <errno.h>
#include <sys/stat.h>
#include <string.h>
#include <time.h>
#include <pthread.h>
#include <math.h>
#define goal 98931313
typedef struct arguments {
int start;
int n;
} arguments_t;
void factorise(int n) {
pthread_t t1, t2, t3, t4;
//1st pthread
arguments_t t1_arguments;
t1_arguments.start = 0;
t1_arguments.n = n;
//2nd pthread
arguments_t t2_arguments;
t2_arguments.start = 250;
t2_arguments.n = n;
//3rd pthread
arguments_t t3_arguments;
t3_arguments.start = 500;
t3_arguments.n = n;
//4th pthread
arguments_t t4_arguments;
t4_arguments.start = 750;
t4_arguments.n = n;
void *find_factors();
//creating threads
pthread_create(&t1, NULL, find_factors, &t1_arguments);
pthread_create(&t2, NULL, find_factors, &t2_arguments);
pthread_create(&t3, NULL, find_factors, &t3_arguments);
pthread_create(&t4, NULL, find_factors, &t4_arguments);
pthread_join(t1, NULL);
pthread_join(t2, NULL);
pthread_join(t3, NULL);
pthread_join(t4, NULL);
}
//Using 3 loops, 1 loop represents one value that we need to find, and go throught it until 98931313 not will be find.
void *find_factors(arguments_t *args){
int a, b, c;
for(a=args->start;a<args->start+250;a++){
for(b=0;b<1000;b++){
for(c=0;c<1000;c++){
if(a*b*c == args->n){
printf("solution is %d, %d, %d\n", a, b, c);// Printing out the answer
}
}
}
}
}
// Calculate the difference between two times.
long long int time_difference(struct timespec *start, struct timespec *finish, long long int *difference) {
long long int ds = finish->tv_sec - start->tv_sec;
long long int dn = finish->tv_nsec - start->tv_nsec;
if(dn < 0 ) {
ds--;
dn += 1000000000;
}
*difference = ds * 1000000000 + dn;
return !(*difference > 0);
}
//Prints elapsed time
int main() {
struct timespec start, finish;
long long int time_elapsed;
clock_gettime(CLOCK_MONOTONIC, &start);
factorise(goal); //This is our goal = 98931313
clock_gettime(CLOCK_MONOTONIC, &finish);
time_difference(&start, &finish, &time_elapsed);
printf("Time elaipsed was %lldns or %0.9lfs\n", time_elapsed, (time_elapsed/1.0e9));
return 0;
}

Answer 1

I'll give you a hint:
If you call a function twice manually, you can put its results into two separate variables:
int y0 = f(0);
int y1 = f(1);
You as well can put them into one array:
int y[2];
y[0] = f(0);
y[1] = f(1);
Or into a memory area on heap (obtained via malloc()):
int * y = malloc(2 * sizeof(*y));
y[0] = f(0);
y[1] = f(1);
In the latter two cases, you can replace the two function calls with
for (i = 0; i < 2; i++) {
y[i] = f(i);
}
Another hint:
For a changed number of threads, you will as well have to change your parameter set.
And another hint:
Thread creation, in your case, can be put into a function:
void facthread_create(pthread_t * thread, int start, int n)
{
arguments_t arguments;
arguments.start = start;
arguments.n = n;
void *find_factors();
//creating thread
pthread_create(thread, NULL, find_factors, &arguments);
}
But - there is a caveat: we have a race condition here. As soon as the thread starts, we can return and the stack space occupied by arguments is freed. So we use an improved version here which is useful for cooperation:
We add a field to arguments_t:
typedef struct arguments {
char used;
int start;
int n;
} arguments_t;
We set used to 0:
void facthread_create(pthread_t * thread, int start, int n)
{
arguments_t arguments;
arguments.start = start;
arguments.n = n;
arguments.used = 0;
void *find_factors();
//creating thread
pthread_create(thread, NULL, find_factors, &arguments);
while (!arguments.used); // wait until thread has "really" started
}
Set used to 1 once the data has safely copied:
void *find_factors(arguments_t *args){
arguments_t my_args = *args; // is this valid? Don't remember... If not, do it element-wise...
*args.used = 1; // Inform the caller that it is safe to continue
int a, b, c;
for(a=my_args.start;a<my_args.start+250;a++){
...

Answer 2

You should get a command line parameter (maybe -t for threads). Then instead of calling factorise from main, have a for loop which does the thread create with the parameter which is calculated from the loop number. Something like:
for (int i = 0; i < threads; i++) {
arguments.start = 250 * i;
arguments.n = n;
pthread_start(...)
}
Note that you should allocate the argument structs before the for loop for clarity.
Let me know if you need more help.
Here is some more help:
0) get the number of threads and the skip (in your case 250) from the command line.
1) create a control stuct which contains the args for the thread, the thread id, etc.
2) using the args, allocate the control struct and fill it in.
3) do a for loop to spawn off the treads.
4) do another for loop to wait for the threads to complete.
For some extra complexity, you could introduce a global variable which any thread could set to signal the other threads that the work is done and they should exit. But don't do this until you get the simple case correct.
If you post some updated code, I will help you some more.