Need help consumer/producer shared memory and semaphore (c language)

Question

If I run code I get no result. If I delete sem_post and sem_wait then it works. I have a producer / consumer application which have exchanged data via shared memory.

#include<stdio.h>
#include<stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdbool.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <semaphore.h>
#include <dispatch/dispatch.h>
#include <errno.h>
#include <math.h>

int shmid;
unsigned long long Fibonacci(int n);
typedef struct node_t {
  unsigned long long data;
  int n;
  bool set;
  int id;
} node_t;

typedef struct fibobuff_t {
   char szFiboText[BUFF_SIZE / 2];
   struct node_t naNode[MAX_BUF];
} fibobuff_t;

#define MAX_BUF 5
#define SHM_SIZE 65365
#define BUFF_SIZE 65536

sem_t *empty;
sem_t *full;

void producer(){
    int n =0, i =0;
    fibobuff_t *pFB = shmat(shmid, (void *) 0, 0);
    if(pFB == NULL){
        perror("error");
        exit(1);
    }
    while (true) {
        printf("(%i) Waiting for room... ", i);
        sem_wait(empty);  
        usleep(150 + rand() % 1350);   

        pFB->naNode[i].data = Fibonacci(n++);
        sem_post(full);
        i = (i + 1) % (MAX_BUF);
        if (pFB->naNode[i].set){
            //  sem_wait(empty);
        }
    }
}

void consumer(){
    fibobuff_t *pFB = shmat(shmid, (void *) 0, 0);
    int i = 0;
    while (true) { 
        printf("(%i) Waiting for content... ", i);
        sem_wait(full);

        usleep(150 + rand() % 1600);
        char szTmp[BUFF_SIZE/2] = {0};
        snprintf(szTmp, BUFF_SIZE/2, "%llu ", pFB->naNode[i].data);
        strncat(pFB->szFiboText,szTmp, BUFF_SIZE/2);
        pFB->naNode[i].set = FALSE;
        printf("\tNr. %i = %s\n\n", pFB->naNode[i].n, szTmp);
        i = (i + 1) % (BUFF_SIZE);
        sem_post(empty);
        //sem_post(pmut);
        if (!pFB->naNode[i].set){
            sem_wait(full);
        }
    }
}

int main(void)
{
    int t;
    if ((shmid = shmget(IPC_PRIVATE, BUFF_SIZE, 0666 | IPC_CREAT)) == -1) {
        perror("shmget consumer");
        exit(1);
    }
    fibobuff_t *pFB = shmat(shmid, (void *) 0, 0);

    for (t = 0; t < MAX_BUF; t++) {
        pFB->naNode[t].data = 0;
    }
    empty = sem_open("/empty",O_CREAT,0644,1);
    full = sem_open("/full",O_CREAT,0644,0);

    if(fork()){
        producer(); 
    }else{
        consumer();
    }
}

someone can help. I do not know what goes wrong

That's a lot of code. Try narrowing your problem down. I wouldn't expect many people trying to go through wall of code so big. — zubergu, Dec 08 '15 at 13:20
Thanks . Wait for a while I will look into it . I do not have dispatch.h in ubuntu .installing it :-) — Punit Vara, Dec 08 '15 at 13:41
You are not checking the returned value of the two calls to sem_open. Are they created properly? In consumer(), you also have a second `sem_wait(full)` in `if (!pFB->naNode[i].set)`. Are you sure this is correct? — Richard St-Cyr, Dec 08 '15 at 13:45
`/tmp/ccIgCtTh.o: In function `producer': `so21.c:(.text+0xb2): undefined reference to `Fibonacci'`collect2: error: ld returned 1 exit status` I am getting this error You are not getting this error ? — Punit Vara, Dec 08 '15 at 14:14
unsigned long long Fibonacci(int n) { return (pow(1 + sqrtf(5), n) - pow(1 - sqrtf(5), n)) / (pow(2, n) * sqrtf(5)); } — Daniil Pimenau, Dec 08 '15 at 14:19
undefined reference to `pow' I am using gcc .. -lm ... still generating this error. Use another function instead of it — Punit Vara, Dec 08 '15 at 14:33
I am uploading the code for a while I do not know whether it is what you are looking for or a different . If it does not solve your problem just let me know I will delete the answer. I am just trying to help you — Punit Vara, Dec 08 '15 at 14:42
@DaniilPimenau Do I solve your problem ? Your code has so many warnings and errors. I have just cleared it — Punit Vara, Dec 08 '15 at 14:53

score 0 · Answer 1 · answered Sep 05 '17 at 06:59

In consumer() you have two calls to sem_wait(full); drop the second one.
In consumer() you have i = (i + 1) % (BUFF_SIZE); correct is i = (i + 1) % MAX_BUF.
Note that subsequent runs of your program may behave differently from the first run, since you don't remove the semaphores by sem_unlink(), and their initial values are set when created.

Need help consumer/producer shared memory and semaphore (c language)

1 Answers1