Producer_consumer in c using p threads and semaphore - c

Question

/*Producer_consumer problem in c using semaphores and pthreads*/
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#define RAND_DIVISOR 100000000
#define TRUE 1
typedef int buffer_item;
#define BUFFER_SIZE 5
/* 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);
}
when i compile this using gcc i get the following errors:
cse#cse-Not-Specified:~/11011P0519$ vi producer_consumer2.c
cse#cse-Not-Specified:~/11011P0519$ gcc producer_consumer2.c
/tmp/ccu6fydZ.o: In function `initializeData':
producer_consumer2.c:(.text+0x32): undefined reference to `sem_init'
producer_consumer2.c:(.text+0x4e): undefined reference to `sem_init'
/tmp/ccu6fydZ.o: In function `producer':
producer_consumer2.c:(.text+0xac): undefined reference to `sem_wait'
producer_consumer2.c:(.text+0x11d): undefined reference to `sem_post'
/tmp/ccu6fydZ.o: In function `consumer':
producer_consumer2.c:(.text+0x160): undefined reference to `sem_wait'
producer_consumer2.c:(.text+0x1d1): undefined reference to `sem_post'
/tmp/ccu6fydZ.o: In function `main':
producer_consumer2.c:(.text+0x2ef): undefined reference to `pthread_create'
producer_consumer2.c:(.text+0x32d): undefined reference to `pthread_create'
collect2: ld returned 1 exit status
and when i try using gcc -lpthreads i get
cannot find lpthreads.
How to fix this ?

Answer 1

You need to Link with -lrt or -pthread while using function from semphore.h
compile as below
gcc producer_consumer2.c -pthread
see man sem_init