Producer Consumer segmentation fault (core dumped) - c

Question

Hi im trying to do the producer/consumer problem on a ubuntu virtual image using vmware. I got the code from here : http://macboypro.wordpress.com/2009/05/25/producer-consumer-problem-using-cpthreadsbounded-buffer/ but i just keep getting "segmentation fault (core dumped)". Any help would be great or even a more clean solution to the producer/consumer problem (bounded buffer problem).
Heres the code im using but due to errors i had to take out the '#include "buffer.h"' :
/* buffer.h */
typedef int buffer_item;
#define BUFFER_SIZE 5
/* main.c */
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include "buffer.h"
#define RAND_DIVISOR 100000000
#define TRUE 1
/* The mutex lock */
pthread_mutex_t mutex;
/* the semaphores */
sem_t full, empty;
/* the buffer */
buffer_item buffer[BUFFER_SIZE];
/* buffer counter */
int counter;
pthread_t tid; //Thread ID
pthread_attr_t attr; //Set of thread attributes
void *producer(void *param); /* the producer thread */
void *consumer(void *param); /* the consumer thread */
void initializeData() {
/* Create the mutex lock */
pthread_mutex_init(&mutex, NULL);
/* Create the full semaphore and initialize to 0 */
sem_init(&full, 0, 0);
/* Create the empty semaphore and initialize to BUFFER_SIZE */
sem_init(&empty, 0, BUFFER_SIZE);
/* Get the default attributes */
pthread_attr_init(&attr);
/* init buffer */
counter = 0;
}
/* 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);
/* 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);
}
/* release the mutex lock */
pthread_mutex_unlock(&mutex);
/* signal empty */
sem_post(&empty);
}
}
/* Add an item to the buffer */
int insert_item(buffer_item item) {
/* When the buffer is not full add the item
and increment the counter*/
if(counter < BUFFER_SIZE) {
buffer[counter] = item;
counter++;
return 0;
}
else { /* Error the buffer is full */
return -1;
}
}
/* Remove an item from the buffer */
int remove_item(buffer_item *item) {
/* When the buffer is not empty remove the item
and decrement the counter */
if(counter > 0) {
*item = buffer[(counter-1)];
counter--;
return 0;
}
else { /* Error buffer empty */
return -1;
}
}
int main(int argc, char *argv[]) {
/* Loop counter */
int i;
/* Verify the correct number of arguments were passed in */
if(argc != 4) {
fprintf(stderr, "USAGE:./main.out <INT> <INT> <INT>\n");
}
int mainSleepTime = atoi(argv[1]); /* Time in seconds for main to sleep */
int numProd = atoi(argv[2]); /* Number of producer threads */
int numCons = atoi(argv[3]); /* Number of consumer threads */
/* Initialize the app */
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);
}
/* Sleep for the specified amount of time in milliseconds */
sleep(mainSleepTime);
/* Exit the program */
printf("Exit the program\n");
exit(0);
}

Answer 1

Your code seems correct, except that you don't have prototypes at the top for:
int insert_item(buffer_item item);
int remove_item(buffer_item *item);
I was able to run your program without getting a seg fault after adding those prototypes. Using rand() in a multithreaded app is somewhat dangerous though. When I ran the code with multiple producers, they were all sleeping the same random time and generating the same random item numbers.