Twity 56876 Twity 56876 - 4 months ago 65
C Question

Producer Consumer program using semaphores and pthreads

I have written a code for producer-consumer problem.But I am not getting the output.There is no compilation error,but warning in my program.I am confused.Trying very hard.But can't get it.Please tell me what is wrong in my program.What will be the correct program.I am getting frustrated.Please help guys.
Here is the code-

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include </usr/include/semaphore.h>

#define BUFF_SIZE 5 /* total number of slots */
#define NP 3 /* total number of producers */
#define NC 3 /* total number of consumers */
#define NITERS 4 /* number of items produced/consumed */

typedef struct {
int buf[BUFF_SIZE]; /* shared var */
int in; /* buf[in%BUFF_SIZE] is the first empty slot */
int out; /* buf[out%BUFF_SIZE] is the first full slot */
sem_t full; /* keep track of the number of full spots */
sem_t empty; /* keep track of the number of empty spots */
sem_t mutex; /* enforce mutual exclusion to shared data */
} sbuf_t;

sbuf_t shared;


void *Producer(void *arg) {
int i, item, index;

index = (int) arg;


for (i = 0; i < NITERS; i++) {
/* Produce item */
item = i;

/* Prepare to write item to buf */

/* If there are no empty slots, wait */
sem_wait(&shared.empty);
/* If another thread uses the buffer, wait */
sem_wait(&shared.mutex);
shared.buf[shared.in] = item;
shared.in = (shared.in+1)%BUFF_SIZE;
printf("[P%d] Producing %d ...\n", index, item); fflush(stdout);
/* Release the buffer */
sem_post(&shared.mutex);
/* Increment the number of full slots */
sem_post(&shared.full);

/* Interleave producer and consumer execution */
if (i % 2 == 1) sleep(1);
}
return NULL;
}

void *Consumer(void *arg) {
int i, item, index;

index = (int) arg;
for (i = NITERS; i > 0; i--) {
sem_wait(&shared.full);
sem_wait(&shared.mutex);
item = i;
item = shared.buf[shared.out];
shared.out = (shared.out + 1) % BUFF_SIZE;
printf("[C%d] Consuming %d ...\n", index, item); fflush(stdout);
/* Release the buffer */
sem_post(&shared.mutex);
/* Increment the number of full slots */
sem_post(&shared.empty);

/* Interleave producer and consumer execution */
if (i % 2 == 1) sleep(1);
}
return NULL;
}

int main() {
pthread_t idP, idC;
int index;

sem_init(&shared.full, 0, 0);
sem_init(&shared.empty, 0, BUFF_SIZE);
pthread_mutex_init(&shared.mutex, NULL);
for (index = 0; index < NP; index++) {
/* Create a new producer */
pthread_create(&idP, NULL, Producer, (void*)index);
}
/*create a new Consumer*/
for (index = 0;index < NC;index++) {
pthread_create(&idC, NULL, Consumer, (void*)index);
}
pthread_exit(NULL);
}

Answer

Maybe you should take the Compiler warnings more serious. Incorrect types and undefined functions are usually shown as warning...

I haven't checked the Logic of your program, but the principle should work:

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include </usr/include/semaphore.h>

// for sleep
#include <unistd.h>

#define BUFF_SIZE   5           /* total number of slots */
#define NP          3           /* total number of producers */
#define NC          3           /* total number of consumers */
#define NITERS      4           /* number of items produced/consumed */

typedef struct
{
    int buf[BUFF_SIZE];   /* shared var */
    int in;               /* buf[in%BUFF_SIZE] is the first empty slot */
    int out;              /* buf[out%BUFF_SIZE] is the first full slot */
    sem_t full;           /* keep track of the number of full spots */
    sem_t empty;          /* keep track of the number of empty spots */

    // use correct type here
    pthread_mutex_t mutex;          /* enforce mutual exclusion to shared data */
} sbuf_t;

sbuf_t shared;


void *Producer(void *arg)
{
    int i, item, index;

    index = (int)arg;


    for (i=0; i < NITERS; i++)
    {

        /* Produce item */
        item = i;

        /* Prepare to write item to buf */

        /* If there are no empty slots, wait */
        sem_wait(&shared.empty);
        /* If another thread uses the buffer, wait */
        pthread_mutex_lock(&shared.mutex);
        shared.buf[shared.in] = item;
        shared.in = (shared.in+1)%BUFF_SIZE;
        printf("[P%d] Producing %d ...\n", index, item);
        fflush(stdout);
        /* Release the buffer */
        pthread_mutex_unlock(&shared.mutex);
        /* Increment the number of full slots */
        sem_post(&shared.full);

        /* Interleave  producer and consumer execution */
        if (i % 2 == 1) sleep(1);
    }
    return NULL;
}

void *Consumer(void *arg)
{
    int i, item, index;

    index = (int)arg;
    for (i=NITERS; i > 0; i--) {
        sem_wait(&shared.full);
        pthread_mutex_lock(&shared.mutex);
        item=i;
        item=shared.buf[shared.out];
        shared.out = (shared.out+1)%BUFF_SIZE;
        printf("[C%d] Consuming  %d ...\n", index, item);
        fflush(stdout);
        /* Release the buffer */
        pthread_mutex_unlock(&shared.mutex);
        /* Increment the number of full slots */
        sem_post(&shared.empty);

        /* Interleave  producer and consumer execution */
        if (i % 2 == 1) sleep(1);
    }
    return NULL;
}

int main()
{
    pthread_t idP, idC;
    int index;

    sem_init(&shared.full, 0, 0);
    sem_init(&shared.empty, 0, BUFF_SIZE);
    pthread_mutex_init(&shared.mutex, NULL);
    for (index = 0; index < NP; index++)
    {
        /* Create a new producer */
        pthread_create(&idP, NULL, Producer, (void*)index);
    }
    /*create a new Consumer*/
    for(index=0; index<NC; index++)
    {
        pthread_create(&idC, NULL, Consumer, (void*)index);
    }



    pthread_exit(NULL);
}

I hope this helps.