Segmentation fault in the below c code compiled in linux

Question

we simulate a tandoori chicken lunch buffet restaurant with one chef and multiple guests, which is similar to a single producer/multiple consumers problem. We implement one program with multiple threads, each of which holds either a chef or a guest. We also apply one synchronization tool – semaphores, which can solve an issue for synchronizing common resources with multiple threads. Through this project, we will learn how to create multi-threaded process and how to synchronize threads using semaphores.

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

struct threadInfo
{
int id;
};

/* input variables */
int nofCustomers=4,item,nofChicken=3;
pthread_attr_t attr; /*Set of thread attributes*/
pthread_t chef_t,customer_t[100];
/* the semaphores */
sem_t full, empty;
void *chef(void *param); /* the producer thread */
void *customer(void *param); /* the consumer thread */

void initializeData() 
{

/* 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, nofChicken);

/* Get the default attributes */
pthread_attr_init(&attr);

}

PRODUCER

 /* Producer Thread */
 void *chef(void *param) 
{
 printf("Chef Starts Cooking\n");
 while(1) 
{
  /* acquire the empty lock */
  sem_wait(&empty);

  if(insert_item()) 
  {
     fprintf(stderr, " Producer report error condition\n");
  }
  /* signal full */
  sem_post(&full);
  sleep(1);
 }
 }

cONSUMER

 /* Consumer Thread */
 void *customer(void *param) 
 {
   int toeat=1+rand()%4,ate=0,t=nofCustomers;
   int *id=(int*)param;
   printf("Guest %d arrives and wants to eat %d food\n", id, toeat);
   while(1) 
   {
     /* aquire the full lock */
     sem_wait(&full);

     if(remove_item()) 
     {
      fprintf(stderr, "Consumer report error condition\n");
     }
     else 
     {
   ate++;
       printf("Guest %d eats a tandoori chicken[%d/%d]\n", id,ate,toeat);
      }
     if(ate==toeat)
     {
        nofCustomers--;
    printf("Guest %d finishes and exits\n",id);
     }
     if(nofCustomers==0)
     {
    printf("All guests finish eating and exit\n");
    break ;
     }
     /* signal empty */
     sem_post(&empty);
     sleep(toeat);
   }
 }

iNC IN CRITICAL SECTION

/* Cook food */
int insert_item() 
{
   /* When the item is not full,cook food
   increment the item*/
  if(item <= nofChicken) 
  { 
    item++;
    printf("Chef cooks one tandoori chicken.[%d/%d]\n",item,nofChicken);
    return 0;
   }
   else 
   { /* Error the items are full */
      return -1;
    }
 }

DEC IN CRITICAL SECTION

  /* Eat food */
 int remove_item() {
 /* When the items is/are cooked, eat the item
   i.e.., decrement the item */
  if(item > 0)
  { 
     item--;
     return 0;
   }
   else { /* Error no items */
    return -1;
   }
 }

maIN FUNCTION

 int main()
 {
   /* Loop counter */
   int i;
   struct threadInfo *info;

   //input (Havent written code for input includes nofChicken andnofCustomers

   /* Initialize the app */
   initializeData();

  /* Create the producer thread */
  pthread_create(&chef_t,&attr,chef,NULL);


  /* Create the consumer threads */
  for(i = 1; i <= nofCustomers; i++) 
 {
   info->id=i;
   pthread_create(&customer_t[i],&attr,customer,(void *)info);
 }

 return 0; 
}

Segmentation fault in the BOVE CODE

Answer 1

First, fix these compilation errors:

g++ -std=c++17 -fPIC -g -Wall -Wextra -Wwrite-strings -Wno-parentheses -Wpedantic -Warray-bounds -O2 -Weffc++      39988874.cpp    -o 39988874
39988874.cpp: In function ‘void* chef(void*)’:
39988874.cpp:43:25: error: ‘insert_item’ was not declared in this scope
         if (insert_item()) {
                         ^
39988874.cpp:48:16: error: ‘sleep’ was not declared in this scope
         sleep(1);
                ^
39988874.cpp:36:18: warning: unused parameter ‘param’ [-Wunused-parameter]
 void *chef(void *param)
                  ^~~~~
39988874.cpp: In function ‘void* customer(void*)’:
39988874.cpp:58:68: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int*’ [-Wformat=]
     printf("Guest %d arrives and wants to eat %d food\n", id, toeat);
                                                                    ^
39988874.cpp:63:25: error: ‘remove_item’ was not declared in this scope
         if (remove_item()) {
                         ^
39988874.cpp:67:77: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int*’ [-Wformat=]
             printf("Guest %d eats a tandoori chicken[%d/%d]\n", id,ate,toeat);
                                                                             ^
39988874.cpp:71:54: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int*’ [-Wformat=]
             printf("Guest %d finishes and exits\n",id);
                                                      ^
39988874.cpp:79:20: error: ‘sleep’ was not declared in this scope
         sleep(toeat);
                    ^
39988874.cpp:56:32: warning: unused variable ‘t’ [-Wunused-variable]
     int toeat=1+rand()%4,ate=0,t=nofCustomers;
                                ^
39988874.cpp:81:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
<builtin>: recipe for target '39988874' failed
make: *** [39988874] Error 1

(hint: you'll need #include <unistd.h> for sleep(); also, you'll want int id = ((threadInfo*)param)->id)

Having fixed those, you'll be left with

39988874.cpp: In function ‘int main()’:
39988874.cpp:133:17: warning: ‘info’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         info->id=i;
         ~~~~~~~~^~

Which is quite obviously caused by

struct threadInfo *info;
/* ... */
for (i = 1; i <= nofCustomers; i++) {
    info->id=i;
}

There's your problem. You need to make info point to some valid storage.