Program 8:
AIM: Write a C Program to implement Producer – consumer problem using
semaphores using UNIX/LINUX system calls.
#include
<stdio.h>
#include
<stdlib.h>
#include
<pthread.h>
#include
<semaphore.h>
#define SIZE 5
#define
NUMB_THREADS 6
#define
PRODUCER_LOOPS 2
typedef int
buffer_t;
buffer_t
buffer[SIZE];
int buffer_index;
pthread_mutex_t
buffer_mutex;
sem_t
full_sem; /* when 0, buffer is full */
sem_t empty_sem;
/* when 0, buffer is empty. Kind of
like an index for the
buffer */
void
insertbuffer(buffer_t value) {
if (buffer_index < SIZE) {
buffer[buffer_index++] = value;
} else {
printf("Buffer overflow\n");
}
}
buffer_t
dequeuebuffer() {
if (buffer_index > 0) {
return buffer[--buffer_index]; //
buffer_index-- would be error!
} else {
printf("Buffer underflow\n");
}
return 0;
}
void
*producer(void *thread_n) {
int thread_numb = *(int *)thread_n;
buffer_t value;
int i=0;
while (i++ < PRODUCER_LOOPS) {
sleep(rand() % 10);
value = rand() % 100;
sem_wait(&full_sem); // sem=0:
wait. sem>0: go and decrement it
pthread_mutex_lock(&buffer_mutex);
/* protecting critical section */
insertbuffer(value);
pthread_mutex_unlock(&buffer_mutex);
sem_post(&empty_sem); // post
(increment) emptybuffer semaphore
printf("Producer %d added %d to
buffer\n", thread_numb, value);
}
pthread_exit(0);
}
void *consumer(void
*thread_n) {
int thread_numb = *(int *)thread_n;
buffer_t value;
int i=0;
while (i++ < PRODUCER_LOOPS) {
sem_wait(&empty_sem);
pthread_mutex_lock(&buffer_mutex);
value = dequeuebuffer(value);
pthread_mutex_unlock(&buffer_mutex);
sem_post(&full_sem); // post
(increment) fullbuffer semaphore
printf("Consumer %d dequeue %d
from buffer\n", thread_numb, value);
}
pthread_exit(0);
}
int main(int argc,
int **argv) {
buffer_index = 0;
pthread_mutex_init(&buffer_mutex,
NULL);
sem_init(&full_sem, // sem_t *sem
0, // int pshared. 0 = shared
between threads of process, 1 = shared
between processes
SIZE); // unsigned int value.
Initial value
sem_init(&empty_sem,
0,
0);
pthread_t thread[NUMB_THREADS];
int thread_numb[NUMB_THREADS];
int i;
for (i = 0; i < NUMB_THREADS; ) {
thread_numb[i] = i;
pthread_create(thread + i, // pthread_t
*t
NULL, // const
pthread_attr_t *attr
producer, // void
*(*start_routine) (void *)
thread_numb + i); // void *arg
i++;
thread_numb[i] = i;
// playing a bit with thread and
thread_numb pointers...
pthread_create(&thread[i], //
pthread_t *t
NULL, // const
pthread_attr_t *attr
consumer, // void
*(*start_routine) (void *)
&thread_numb[i]); // void
*arg
i++;
}
for (i = 0; i < NUMB_THREADS; i++)
pthread_join(thread[i], NULL);
pthread_mutex_destroy(&buffer_mutex);
sem_destroy(&full_sem);
sem_destroy(&empty_sem);
return 0;
}
