pthreads + "private" semaphores issue

Posted this over on stack overflow, but they were no help.

This is an assignment i'm working on, it must use semaphores, not mutex.

Code:

---

#include <stdio.h>
#include <pthread.h>
#include <assert.h>
#include <unistd.h>
#include <semaphore.h>
#include <fcntl.h>
sem_t *ab, *ac, *ad, *de, *ce, *bf, *ef;

void *a(void *arg) {
        printf("Entering A...\n");
        sleep(1);
        printf("Exiting A...\n");
        assert(sem_post(ab)==0);
        assert(sem_post(ac)==0);
        assert(sem_post(ad)==0);
        pthread_exit((void *)99);
}

void *b(void *arg) {
        assert(sem_wait(ab)==0);
        printf("Entering B...\n");
        sleep(1);
        printf("Exiting B...\n");
        assert(sem_post(bf)==0);
        pthread_exit((void *)99);
}

void *c(void *arg) {
        assert(sem_wait(ac)==0);
        printf("Entering C...\n");
        sleep(1);
        printf("Exiting C...\n");
        assert(sem_post(ce)==0);
        pthread_exit((void *)99);
}

void *d(void *arg) {
        assert(sem_wait(ad)==0);
        printf("Entering D...\n");
        sleep(1);
        printf("Exiting D...\n");
        assert(sem_post(de)==0);
        pthread_exit((void *)99);
}

void *e(void *arg) {
        assert(sem_wait(ce)==0);
        assert(sem_wait(de)==0);
        printf("Entering E...\n");
        sleep(1);
        printf("Exiting E...\n");
        assert(sem_post(ef)==0);
        pthread_exit((void *)99);
}

void *f(void *arg) {
        assert(sem_wait(bf)==0);
        assert(sem_wait(ef)==0);
        printf("Entering F...\n");
        sleep(1);
        printf("Exiting F...\n");
        pthread_exit((void *)99);
}


int main() {
        pthread_t _a, _b, _c, _d, _e, _f;
        int r1, r2, r3, r4, r5, r6;

        ab=sem_open("foobar", O_CREAT, 0700, 0);
        ac=sem_open("foobar", O_CREAT, 0700, 0);
        ad=sem_open("foobar", O_CREAT, 0700, 0);
        ce=sem_open("foobar", O_CREAT, 0700, 0);
        de=sem_open("foobar", O_CREAT, 0700, 0);
        ef=sem_open("foobar", O_CREAT, 0700, 0);
        bf=sem_open("foobar", O_CREAT, 0700, 0);

        assert(pthread_create(&_a, NULL, a, &r1) == 0);
        assert(pthread_create(&_b, NULL, b, &r2) == 0);
        assert(pthread_create(&_c, NULL, c, &r3) == 0);
        assert(pthread_create(&_d, NULL, d, &r4) == 0);
        assert(pthread_create(&_e, NULL, e, &r5) == 0);
        assert(pthread_create(&_f, NULL, f, &r6) == 0);

        assert(pthread_join(_a, NULL) == 0);
        assert(pthread_join(_b, NULL) == 0);
        assert(pthread_join(_c, NULL) == 0);       
        assert(pthread_join(_d, NULL) == 0);
        assert(pthread_join(_e, NULL) == 0);
        assert(pthread_join(_f, NULL) == 0);

        assert( sem_close(ab)==0 );
        assert( sem_close(ac)==0 );
        assert( sem_close(ad)==0 );
        assert( sem_close(ce)==0 );
        assert( sem_close(de)==0 );
        assert( sem_close(bf)==0 );
        assert( sem_close(ef)==0 );
 
        return 0;
}

---

Its pretty simple, but for some reason its not executing in the right order. It is far from consistent, but always incorrect Here is one output:

Entering A...
Entering B... <----sem_post(ab) has not even been called yet
Exiting A...
Entering C...
Entering D...
Exiting B...
Exiting D...
Exiting C...
Entering E...
Entering F...
Exiting F...
Exiting E...

The proper order should follow these:

A->B, A->C, A->D, C->E, D->E, B->F, E->F

(i.e A->B means B must finish before A can start)

I feel like i'm missing something regarding the semaphores but I can't figure out what. Any help on this would be greatly appreciated

So are you in the same class as this guy: http://cboard.cprogramming.com/c-pro..._init-not.html
Or did you just make a new account so that you could pretend I didn't already tell you to check your return values?


Quzah.

Didn't see that post, it is the same class tho im sure of it.

What return values are you referring to that I have not already used an assert on?

The program works but the threads aren't executing correctly(and im guessing the other guys isnt either, it looks the same as mine.
I changed it a bit heres the updated code:

Code:

---

#include <stdio.h>
#include <pthread.h>
#include <assert.h>
#include <unistd.h>
#include <semaphore.h>
#include <fcntl.h>
sem_t ab, ac, ad, de, ce, bf, ef;

void *a(void *arg) {
        printf("Entering A...\n");
        //sleep(1);
        printf("Exiting A...\n");
        assert(sem_post(&ab)==0);
        assert(sem_post(&ac)==0);
        assert(sem_post(&ad)==0);
        pthread_exit((void *)99);
}

void *b(void *arg) {
        assert(sem_wait(&ab)==0);
        printf("Entering B...\n");
        //sleep(1);
        printf("Exiting B...\n");
        assert(sem_post(&bf)==0);
        pthread_exit((void *)99);
}

void *c(void *arg) {
        assert(sem_wait(&ac)==0);
        printf("Entering C...\n");
        //sleep(1);
        printf("Exiting C...\n");
        assert(sem_post(&ce)==0);
        pthread_exit((void *)99);
}

void *d(void *arg) {
        assert(sem_wait(&ad)==0);
        printf("Entering D...\n");
        //sleep(1);
        printf("Exiting D...\n");
        assert(sem_post(&de)==0);
        pthread_exit((void *)99);
}

void *e(void *arg) {
        assert(sem_wait(&ce)==0);
        assert(sem_wait(&de)==0);
        printf("Entering E...\n");
        //sleep(1);
        printf("Exiting E...\n");
        assert(sem_post(&ef)==0);
        pthread_exit((void *)99);
}

void *f(void *arg) {
        assert(sem_wait(&bf)==0);
        assert(sem_wait(&ef)==0);
        printf("Entering F...\n");
        //sleep(1);
        printf("Exiting F...\n");
        pthread_exit((void *)99);
}

int main() {
        pthread_t _a, _b, _c, _d, _e, _f;
        int r1, r2, r3, r4, r5, r6;

        sem_init(&ab,0,1);
          sem_init(&ac,0,1);
        sem_init(&ad,0,1);
        sem_init(&ce,0,1);
        sem_init(&de,0,1);
        sem_init(&ef,0,1);
        sem_init(&bf,0,1);

        assert(pthread_create(&_a, NULL, a, &r1) == 0);
        assert(pthread_create(&_b, NULL, b, &r2) == 0);
        assert(pthread_create(&_c, NULL, c, &r3) == 0);
        assert(pthread_create(&_d, NULL, d, &r4) == 0);
        assert(pthread_create(&_e, NULL, e, &r5) == 0);
        assert(pthread_create(&_f, NULL, f, &r6) == 0);

        assert(pthread_join(_a, NULL) == 0);
        assert(pthread_join(_b, NULL) == 0);
        assert(pthread_join(_c, NULL) == 0);       
        assert(pthread_join(_d, NULL) == 0);
        assert(pthread_join(_e, NULL) == 0);
        assert(pthread_join(_f, NULL) == 0);

        assert( sem_destroy(&ab)==0 );
        assert( sem_destroy(&ac)==0 );
        assert( sem_destroy(&ad)==0 );
        assert( sem_destroy(&ce)==0 );
        assert( sem_destroy(&de)==0 );
        assert( sem_destroy(&bf)==0 );
        assert( sem_destroy(&ef)==0 );
 
        return 0;
}

---