Question about consumer and producer threads - c

Question

I'm having an issue with my sleep cycles in the ProducerConsumer.h file. If I comment out the sleep(rnum) the program will access the line printf("producer produced %d\n", item); If it's not commented out it will never access that line and I cant figure out why.
Here is my code it's in 3 separate files I would be grateful of any help thank you.
buffer.h:
typedef int buffer_item;
#define BUFFER_SIZE 5
int insert_item(buffer_item item);
int remove_item(buffer_item *item);
ProducerConsumer.h:
#include <stdlib.h> /* required for rand() */
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <iostream>
#include "buffer.h"
#define RAND_DIVISOR 100000000;
#define TRUE 1
int counter;
buffer_item buffer[BUFFER_SIZE];
pthread_mutex_t mutex;
sem_t full, empty;
/* Producer Thread */
void *producer(void *param) {
buffer_item item;
while(TRUE) {
/* sleep for a random period of time */
int rNum = rand() / RAND_DIVISOR;
sleep(rNum);
printf("producer produced %d\n", item);
/* generate a random number */
item = rand();
/* acquire the empty lock */
sem_wait(&empty);
/* acquire the mutex lock */
pthread_mutex_lock(&mutex);
if(insert_item(item)) {
fprintf(stderr, " Producer report error condition\n");
} else {
printf("producer produced %d\n", item);
}
/* release the mutex lock */
pthread_mutex_unlock(&mutex);
/* signal full */
sem_post(&full);
}
}
/* Consumer Thread */
void *consumer(void *param) {
buffer_item item;
while(TRUE) {
/* sleep for a random period of time */
int rNum = rand() / RAND_DIVISOR;
sleep(rNum);
/* aquire the full lock */
sem_wait(&full);
/* aquire the mutex lock */
pthread_mutex_lock(&mutex);
if(remove_item(&item)) {
fprintf(stderr, "Consumer report error condition\n");
} else {
printf("consumer consumed %d\n", item);`enter code here`
}
/* release the mutex lock */
pthread_mutex_unlock(&mutex);
/* signal empty */
sem_post(&empty);
}
}
int insert_item(buffer_item item) {
if(counter < BUFFER_SIZE) {
buffer[counter] = item;
counter++;
return 0;
} else {
return -1;
}
}
int remove_item(buffer_item *item) {
if(counter > 0) {
*item = buffer[(counter-1)];
counter--;
return 0;
} else {
return -1;
}
}
main.cpp:
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <unistd.h>
#include "ProducerConsumer.h"
#include "buffer.h"
pthread_t tid;
pthread_attr_t attr;
void initializeData()
{
pthread_mutex_init(&mutex, NULL);
sem_init(&full, 0, 0);
sem_init(&empty, 0, BUFFER_SIZE);
pthread_attr_init(&attr);
counter = 0;
}
int main() {
int i;
int numProd = 5; /* Number of producer threads */
int numCons = 5; /* Number of consumer threads */
initializeData();
/* Create the producer threads */
for(i = 0; i < numProd; i++) {
/* Create the thread */
pthread_create(&tid,&attr,producer,NULL);
}
/* Create the consumer threads */
for(i = 0; i < numCons; i++) {
/* Create the thread */
pthread_create(&tid,&attr,consumer,NULL);
}
void *producer(void *param);
void *consumer(void *param);
/* Exit the program */
printf("Exit the program\n");
exit(0);
}

Answer 1

The RAND_MAX value is likely at least 32767, causing the the following line:
int rNum = rand() / RAND_DIVISOR;// defined as 100000000
to most always set rNum == 0.
Change statement to get a non-zero value:
int rNum = 1 + rand() % 10;// yields 1-10
Also, call srand() one time, and before using rand(). eg:
void *producer(void *param) {
buffer_item item;
srand((unsigned) time(&t));
...