Consumer Producer issue in c - c

Question

Hey so I'm doing a simple producer problem but for some reason my producer runs through and then my consumer runs, even though my producer should be stopped once it can't get the semaphore initialized to 15:
#define _REENTRANT
#define BUFFER_SIZE 15
#define SHMKEY ((key_t) 7890)
//The buffer should be treated as circular buffer
#define BUFFER_WRAP(x) x%BUFFER_SIZE
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <semaphore.h>
#include <stdbool.h>
//headers
void* producerFunc(void *);
void* consumerFunc(void *);
//Structures
typedef struct
{
char* value;
} shared_mem;
typedef struct
{
int value;
} shared_dat;
//You will require 3 semaphores;
sem_t empty;
sem_t full;
sem_t crit_sec;
int start = 0;
int end = 0;
shared_mem *buffer;
//while(fscanf(fp,"%c",&newChar) != EOF)
char newChar;
FILE* fp;
shared_dat *counter;
//To compile program use the command:
//gcc name_of_program.c -lpthread -lrt
int main(void){
fp = fopen("mytest.dat", "r");
/******************init everything: threads, sems, shmem**********/
int r=0;
int i;
int shmid; /* shared memory ID */
pthread_t producer[1]; /* process id for thread 1 */
pthread_t consumer[1]; /* process id for thread 2 */
pthread_attr_t attr; /* attribute pointer array */
int status;
char *shmadd;
shmadd = (char *) 0;
int value, value1;
//create shared memory seg, if return -1 then print error
if ((shmid = shmget (SHMKEY, sizeof(int), IPC_CREAT | 0666)) < 0){
perror ("shmget");
exit (1);
}
//connect process to shared memory segment. If return is -1 then print error
if ((buffer = (shared_mem *) shmat (shmid, shmadd, 0)) == (shared_mem *) -1){
perror ("shmat");
exit (0);
}
//set the
char buffer_array[15];
buffer->value = buffer_array;
counter = (shared_dat *) malloc(sizeof(shared_dat));
/* initialize shared memory to 0 */
counter->value = 0 ;
sem_init(&empty,0,BUFFER_SIZE);
sem_init(&full,0,0);
sem_init(&crit_sec,0,1);
printf("1 - I am here %d in pid %d\n",r,getpid());
fflush(stdout);
/* Required to schedule thread independently.
Otherwise use NULL in place of attr. */
pthread_attr_init(&attr);
pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM); /* system-wide contention */
/* end to schedule thread independently */
/* Create the threads */
pthread_create(&producer[0], &attr, producerFunc, NULL);
pthread_create(&consumer[0], &attr, consumerFunc, NULL);
/* Wait for the threads to finish */
pthread_join(producer[0], NULL);
pthread_join(consumer[0], NULL);
/***************once threads finished and * reached in buffer************/
printf("from parent counter = %d\n", counter->value);
printf("---------------------------------------------------------------------------\n");
printf("\t\t End of simulation\n");
sem_destroy(&empty);
sem_destroy(&full);
sem_destroy(&crit_sec);
//release shared mem with IPC_RMID and print "end"
if ((shmctl (shmid, IPC_RMID, (struct shmid_ds *) 0)) == -1){
perror ("shmctl");
exit (-1);
}
fclose(fp);
exit(0);
}
void* producerFunc(void *arg){
bool finished = false;
while(!finished){
sem_wait(&empty);
sem_wait(&crit_sec);
end++;
if(fscanf(fp,"%c",&newChar) != EOF){
buffer->value[BUFFER_WRAP(end)] = newChar;
printf("%c",newChar);
}else{buffer->value[BUFFER_WRAP(end)] = '*';
finished = true;
}
sem_post(&crit_sec);
sem_post(&full);
}
}
void* consumerFunc(void *arg){
bool finished = false;
char val;
while(!finished){
sem_wait(&full);
sem_wait(&crit_sec);
start++;
//sleep for 1 sec
sleep(1);
if((val = buffer->value[BUFFER_WRAP(start)]) != '*'){
printf("Consuming: %c\n",val);
counter->value++;
}else{finished = true;}
sem_post(&crit_sec);
sem_post(&empty);
}
}
For some reason the producer isn't blocked after 15 letters are put into the buffer.

Answer 1

With consumer calling
sem_post(&empty);
you are ensuring more steps than 15 to the producer.
Also note that in your shmget() call you are assuming that
sizeof(int) >= sizeof(struct shared_mem)
which is probably correct until you don't add fields to the struct

Answer 2

So my solution I can't exactly explain but I compiled the code on the machines at school running windows 7. I use a mac. I know the issue was with the options I used to compile.
I needed to use the command on the school computers:
gcc -o ass3 ass3.c -lpthread -lrt
This made the semaphores work. This same command doesn't work on my mac. Apparently that -lrt option doesn't work on mac. Does anyone know why or what the equivalent is so I can get this to work on my home computer?