flipping

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <time.h>
#include <stdint.h>

#define _NUMBER_OF_FLIPS 1
#define _NUMBER_OF_COINS 20
#define _NUMBER_OF_PEOPLE 10000

char coins[_NUMBER_OF_COINS];

pthread_mutex_t lock;
pthread_mutex_t locks[_NUMBER_OF_COINS];

struct person {
    pthread_t tid;
};
struct person people[_NUMBER_OF_PEOPLE];

void *flip_coins_first(void *arg) {
    pthread_mutex_lock(&lock);
    for (int i = 0; i < _NUMBER_OF_COINS; i++) {
        for (int j = 0; j < _NUMBER_OF_FLIPS; j++) {
            if (coins[i] == 'X') {
                coins[i] = '0';
            } else {
                coins[i] = 'X';
            }
        }
    }
    pthread_mutex_unlock(&lock);
    return NULL;
}

void *flip_coins_second(void *arg) {
    int idx = (intptr_t) arg;
    pthread_mutex_lock(&locks[idx]);
    for (int j = 0; j < _NUMBER_OF_FLIPS; j++) {
        if (coins[idx] == 'X') {
            coins[idx] = '0';
        } else {
            coins[idx] = 'X';
        }
    }
    pthread_mutex_unlock(&locks[idx]);
    return NULL;
}

int main(int argc, char *argv[]) {
    pthread_mutex_init(&lock, NULL);
    for (int i = 0; i < _NUMBER_OF_COINS; i++) {
        pthread_mutex_init(&locks[i], NULL);
    }
    pthread_t orig_tid = pthread_self();
    for (int i = 0; i < _NUMBER_OF_COINS; i++) {
        coins[i] = '0';
    }
    clock_t begin = clock();
    printf("coins: %s (start - global lock)\n", coins);
    for (int i = 0; i < _NUMBER_OF_PEOPLE; i++) {
        int err = pthread_create(&people[i].tid, NULL, flip_coins_first,
                                 NULL);
        if (err != 0) {
            printf("Can't spawn thread %d", i);
        }
    }
    for (int i = 0; i < _NUMBER_OF_PEOPLE; i++) {
        (void) pthread_join(people[i].tid, NULL);
    }
    printf("coins: %s (end - global lock)\n", coins);
    pthread_mutex_destroy(&lock);
    clock_t end = clock();
    double time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
    printf("%d threads x %d flips: %f ms\n\n", _NUMBER_OF_PEOPLE,
           _NUMBER_OF_FLIPS, time_spent);
    begin = clock();
    printf("coins: %s (start - local lock)\n", coins);
    for (int i = 0; i < _NUMBER_OF_PEOPLE; i++) {
        for (int j = 0; j < _NUMBER_OF_COINS; j++) {
            int err = pthread_create(&people[i].tid, NULL, flip_coins_second,
                                     (void *) (intptr_t) j);
            if (err != 0) {
                printf("Can't spawn thread %d", i);
            }
        }
    }
    for (int i = 0; i < _NUMBER_OF_PEOPLE; i++) {
        (void) pthread_join(people[i].tid, NULL);
    }
    printf("coins: %s (end - local lock)\n", coins);
    end = clock();
    time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
    printf("%d threads x %d flips: %f ms\n", _NUMBER_OF_PEOPLE,
           _NUMBER_OF_FLIPS, time_spent);
    for (int i = 0; i < _NUMBER_OF_COINS; i++) {
        pthread_mutex_destroy(&locks[i]);
    }

    return 0;
}