critical_section.c

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

int turn = 0;

void some_routine(void) {
    // Some code here
}

int critical_section() {
    // Some code here
}

void loop() {
    while(turn != 0) {
        some_routine();
    }

    critical_section();
    turn = 0;
}

int main(void) {
    int i;
    for(i = 0; i < 100; i++) {
        loop();
    }
    
    return 0;
}