How to make 2 threads run for a certain amount of time

[forevermirin]

I'm working on my program where I want thread 1 to run for 2.1 seconds, after 2.1 seconds I want thread 2 to run for 3.4 seconds and then it needs to switch back to thread 1. I've managed to make both threads run, but without the given time. It is required that I use 2 threads.

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


int main() {


    void* taskOne();
    void* taskTwo();


    pthread_attr_t tattr;
    pthread_attr_init(&tattr);


    pthread_t thread1, thread2;


    double seconds1 = 2.1;
    double seconds2 = 3.4;




    pthread_create(&thread1, &tattr, taskOne, NULL);
    pthread_create(&thread2, &tattr, taskTwo, NULL);


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


    return 0;
}


void* taskOne() {
    int i, j, m, n;
    while (1) {
        for (i = 0; i < 5; i++) {
            for (j = 1; j <= 8; j++) {
                printf("thread: 1 periodnumber: %i\n", j);
                for (m = 0; m <= 1250; m++)
                    for (n = 0; n <= 250000; n++);




            }
        }
    }
}


void* taskTwo() {
    int i, j, m, n;
    while (1) {
        for (i = 0; i < 5; i++) {
            for (j = 1; j <= 8; j++) {
                printf("thread: 2 periodnumber: %i\n", j);
                for (m = 0; m <= 2750; m++)
                    for (n = 0; n <= 250000; n++);




            }
        }
    }

}