A rather primitive Semaphore implementation in C using pthreads

semaphor.c

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

/* Stupid implementation of C semaphores with pthreads.
 * Used as mutex for counting a variable below.
 *
 * compile with:
 *
 *   cc semaphor.c -o sam -lpthread -Wall -Wextra -std=c99 -Os
 *
 */

typedef struct {
    pthread_cond_t cond;
    pthread_mutex_t mtx;
    volatile unsigned N;
} Sam;

////////////////////////////////////////

#define SAM_INIT(n)                    \
{                                      \
    .cond = PTHREAD_COND_INITIALIZER,  \
    .mtx  = PTHREAD_MUTEX_INITIALIZER, \
    .N    = n                          \
};

////////////////////////////////////////

void sam_init(Sam * ps, int N) {
    pthread_mutex_init(&ps->mtx,NULL);
    pthread_cond_init(&ps->cond,NULL);
    ps->N = N;
}

////////////////////////////////////////

void sam_destroy(Sam * ps) {
    pthread_cond_destroy(&ps->cond);
    pthread_mutex_destroy(&ps->mtx);
}

////////////////////////////////////////

void sam_acquire(Sam * ps) {
    pthread_mutex_lock(&ps->mtx);
    while(ps->N == 0) {
        pthread_cond_wait(&ps->cond,&ps->mtx);
    }

    --(ps->N);
    pthread_mutex_unlock(&ps->mtx);
}

////////////////////////////////////////

void sam_release(Sam * ps) {
    pthread_mutex_lock(&ps->mtx);
    ++(ps->N);
    pthread_mutex_unlock(&ps->mtx);
    pthread_cond_signal(&ps->cond);
}

////////////////////////////////////////
////////////////////////////////////////
////////////////////////////////////////

static const int N = 20;
static const int Z = 200000;
static int COUNTER = 0;

void *thread_func(void *semaphore) {
    Sam * mumm = semaphore;

    sam_acquire(mumm);
    for(int i = 0; i < Z; i++) {
        ++COUNTER;
    }
    sam_release(mumm);
    return NULL;
}

////////////////////////////////////////

int main(void) {
    Sam Mumm = SAM_INIT(1);

    pthread_t threads[N];
    for(int i = 0; i < N; i++) {
        pthread_create(&threads[i],NULL,thread_func,&Mumm);
    }

    for(int i = 0; i < N; i++) {
        pthread_join(threads[i],NULL);
    }

    fprintf(stderr,"%d\n", COUNTER);
    return EXIT_SUCCESS;
}

now what should Counter be?200000 or 4000000(which is 20*200000)?

@PariaHja: It should be 4000000 since the semaphore here acts as mutex where every of the 20 threads counts up the counter 200000 times.

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