Personal Implementation of Signals using pipes

milk.c

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

void s_init(int **S, int k);

void s_destroy(int *S);

void s_wait(int *S);

void s_signal(int *S);

void s_check_pipe(int *S) {
    if (S == NULL) {
        printf("The pipe is NULL.\n");
        exit(1);
    }

    if (sizeof(S) != (sizeof(int) * 2)) {
        printf("The pipe doesn't have the correct size.\n");
        exit(1);
    }
}

void s_init(int **S, int k) {
    if (k < 0) {
        printf("K must not be negative.\n");
        exit(1);
    }

    *S = malloc(sizeof(int) * 2);

    if (pipe(*S) == -1) {
        printf("Couldn't create the pipe.\n");
        exit(1);
    }

    for (int i = 0; i < k; i++) {
        s_signal(*S);
    }
}

void s_destroy(int *S) {
    s_check_pipe(S);

    close(S[0]);
    close(S[1]);
}

void s_wait(int *S) {
    s_check_pipe(S);

    char ctr;
    if (read(S[0], &ctr, 1) != 1) {
        printf("Could not read from the pipe.\n");
        exit(1);
    }
}

void s_signal(int *S) {
    s_check_pipe(S);

    char ctr = 'X';
    if (write(S[1], &ctr, 1) != 1) {
        printf("Could not write to the pipe.\n");
        exit(1);
    }
}

int *s1;
int *s2;

_Noreturn void *t1(void *arg);

_Noreturn void *t2(void *arg);

int main() {
    printf("[Main] Generating semaphores...\n");

    s_init(&s1, 1);
    s_init(&s2, 0);

    printf("[Main] Starting threads...\n");

    pthread_t ts[2];
    if (pthread_create(&ts[0], NULL, (void *(*)(void *)) t1, (void *) 0) != 0) {
        printf("[Main] Could not create thread T1.\n");
        return 1;
    }

    sleep(5);
    if (pthread_create(&ts[1], NULL, (void *(*)(void *)) t2, (void *) 1) != 0) {
        printf("[Main] Could not create thread T2.\n");
        return 1;
    }

    int ts_size = sizeof(ts) / sizeof(ts[0]);

//    while (1) {
//        sleep(1);
//        for (int i = 0; i < ts_size; i++) {
//            if (pthread_kill(ts[i], 0) == ESRCH) {
//                printf("[Main] T%d is dead.", i + 1);
//            }
//        }
//    }

    for (int i = 0; i < ts_size; i++) {
        if (pthread_join(ts[i], NULL) != 0) {
            printf("[Main] Could not join thread T%d.\n", i + 1);
            return 1;
        }
    }

    printf("[Main] All threads returned.\n");

    printf("[Main] Destroying semaphores...\n");

    s_destroy(s1);
    s_destroy(s2);

    return 0;
}

int milk = 0;

void testMilk(char *prefix) {
    if (milk < 1) {
        printf("[%s] Not enough milk! Buying some...\n", prefix);
        sleep(3);
        milk++;
        printf("[%s] Bought!\n", prefix);
    } else {
        printf("[%s] Milk available. Using some...\n", prefix);
        sleep(3);
        milk--;
        printf("[%s] Used!\n", prefix);
    }

    printf("[%s] Fridge: %d milk\n", prefix, milk);
}

_Noreturn void *t1(void *arg) {
    while (1) {
        s_wait(s1);
        testMilk("T1"); // SC
        s_signal(s2);

        sleep(1);
    }
}

_Noreturn void *t2(void *arg) {
    while (1) {
        s_wait(s2);
        testMilk("T2"); // SC
        s_signal(s1);

        sleep(1);
    }
}

signal.c

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

void s_init(int **S, int k);

void s_destroy(int *S);

void s_wait(int *S);

void s_signal(int *S);

void s_check_pipe(int *S) {
    if (S == NULL) {
        printf("The pipe is NULL.\n");
        exit(1);
    }

    if (sizeof(S) != (sizeof(int) * 2)) {
        printf("The pipe doesn't have the correct size.\n");
        exit(1);
    }
}

void s_init(int **S, int k) {
    if (k < 0) {
        printf("K must not be negative.\n");
        exit(1);
    }

    *S = malloc(sizeof(int) * 2);

    if (pipe(*S) == -1) {
        printf("Couldn't create the pipe.\n");
        exit(1);
    }

    for (int i = 0; i < k; i++) {
        s_signal(*S);
    }
}

void s_destroy(int *S) {
    s_check_pipe(S);

    close(S[0]);
    close(S[1]);
}

void s_wait(int *S) {
    s_check_pipe(S);

    char ctr;
    if (read(S[0], &ctr, 1) != 1) {
        printf("Could not read from the pipe.\n");
        exit(1);
    }
}

void s_signal(int *S) {
    s_check_pipe(S);

    char ctr = 'X';
    if (write(S[1], &ctr, 1) != 1) {
        printf("Could not write to the pipe.\n");
        exit(1);
    }
}

int *s1;

int main() {
    printf("Creating sem.\n");
    s_init(&s1, 1);

    printf("Waiting signal.\n");
    s_wait(s1);

    printf("Sending signal.\n");
    s_signal(s1);

    printf("Waiting signal.\n");
    s_wait(s1);

    printf("Destroying sem.\n");
    s_destroy(s1);

    printf("Done. Bye!\n");

    return 0;
}