Producer-Consumer problem

[fkpac]

Hi everybody! I have written this producer-consumer code. The producer creates random integers, and the consumer prints them. And it works. Only, not in the way I expected!!! If you compile (don't forget gcc -lpthread option!) and run it, you see that generally (not always) the producter produces everything, and then the consumer prints everything. But I did put the pthread_cond_signal in the producer's code!!! But at that point, the consumers continues to sleep
Any ideas??

 #include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<pthread.h>
#include<errno.h>
#include <time.h>
#define true 1
#define N 5
 
struct node {
   int info;
   struct node * next;
};
 
static struct node * head=NULL;
static int i=0;
 
void inserisci (struct node * p)
{
  struct node * aux=head;
 
  head=p;
  p->next=aux;
 
  /*
  if (head==NULL) head=p;
  else{
  
  while (aux->next!=NULL)
    aux=aux->next;
  aux->next=p;
  p->next=NULL;
  }*/
 
}
 
struct node * produci(void)
{
  struct node *point=malloc(sizeof(struct node));
  point->info=rand() % 100;
  point->next=NULL;
  return(point);
}
 
struct node * estrai(void)
{
  struct node * aux,*aux2;
  aux=head;
  if (head==NULL)
    {printf("Lista vuota (non dovrebbe succedere)\n"); return(NULL);}
  else{
    
    if (aux->next==NULL)
      {
    head=NULL;
    return(aux);
      }
    else{
    while(aux->next!=NULL)
      {aux2=aux;
    aux=aux->next;}
    
    aux2->next=NULL;
    
    }
  }
  return(aux);
}
 
 
 
 
static pthread_mutex_t mtx=PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t cond=PTHREAD_COND_INITIALIZER;
 
void Pthread_mutex_lock(pthread_mutex_t *mtx)
   { int err;
   if ( ( err=pthread_mutex_lock(mtx)) != 0 ) {
      errno=err;
      perror("lock");
      pthread_exit((void *)17); /* maybe */
      printf("Printf errore lock\n");
   }
   else printf("locked\n");}
 
 
void Pthread_mutex_unlock(pthread_mutex_t *mtx) {
 
 int err;
   if ( ( err=pthread_mutex_unlock(mtx)) != 0 ) {
      errno=err;
      perror("lock");
      pthread_exit((void *)18); /* maybe */
      printf("Printf errore unlock\n");
   }
   
 
  /* as above */
   else printf("unlocked\n");
}
 
 
static void* consumer (void*arg) {
  struct node * p;
  printf("Sono il consumatore\n");
  while(true) {/*printf("Ciclo while consumatore\n");*/
    Pthread_mutex_lock(&mtx);
    while (head == NULL){
      printf("Mi metto ad aspettare\n");
      pthread_cond_wait(&cond, &mtx);
      printf("Waken up!\n"); fflush(stdout);
      }
    /*printf("Sto per estrarre\n");*/
    p=estrai();
    /*printf("Ho estratto\n");*/
    Pthread_mutex_unlock(&mtx);
    /* elaborazione p ... ... */ 
    printf("%d.Sono il consumatore: il valore che mi è stato passato è: %d\n",i,p->info);
  }
  return (void*)0;}
 
 
static void* producer (void*arg) {
  struct node * p;
  for (i=0; i<N; i++) {
    /*printf("Sto per produrre\n");*/
    p=produci();
    /*printf("Ho prodotto\n");*/
    Pthread_mutex_lock(&mtx);
    /*printf("Sto per inserire\n");*/
    inserisci(p);
    printf("Ho inserito, e risveglio il consumer\n");
    pthread_cond_signal(&cond);
    Pthread_mutex_unlock(&mtx);
  }
  return (void*)0;
}
 
 
 
int main (void){
  pthread_t t1,t2;
  int status1,status2;
  printf("Ora creo il consumer\n");
  pthread_create(&t2,NULL,&consumer,NULL);
  printf("Creato il consumer\n");
  printf("Ora creo il producer\n");
  pthread_create(&t1,NULL,&producer,NULL);
  printf("Creato il producer\n");
 
  /* pthread_create(&t2,NULL,&consumer,NULL);*/
 
  sleep(2);
  pthread_join(t1,(void*) &status1);
  /*  pthread_cancel(t2);
      pthread_join(t2,(void*) &status2);*/
  /* elab return status */
  return 0;
} 
  

[coopstah13]

please edit your post and put the code inside of code tags, it makes it much easier to read

[Rubberman]

School work? Sorry, not allowed on the forums.

[fkpac]

No. I have to write a message server, and I'm trying to decompose it into simpler problems. Anyway, thank you for your nice answer.

[Rubberman]

Well, I've been looking at your code today and have to say that, in my opinion, it is not particularly clearly written, making analysis difficult. I'll try to get back to it a bit later for a better response and critique of the code. Sorry for the delay, but I've been traveling on business this past week.