Thread: Problem with multithreading and pipe

Hi guys, I'm trying to make a script that uses 3 threads that have the task of searching and sending to a memorizer via a pipe, the prime numbers up to a certain n (passed as an input parameter). All 3 threads must work at the same time.
I have 2 problems basically ...
The first is that the threads don't analyze all the numbers, some are skipped, I don't understand why.
The second is that if I launch the main file and then the memorizer, they both stay planted and give no output.
Could you please help me?

Main file

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>


pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int num, n ; 
int fp ; 






void *find_prime_number (void* name){


int *th  = (int *) name;
//while(num <= n ){
 int mynum;
 while (pthread_mutex_lock(&mutex), mynum = num++, pthread_mutex_unlock(&mutex), mynum <= n)
  {


int check = 0; 


////




for(int i=2 ;i<=num/2; i++ ){
   if(num<=n){
       if (num % i==0 ){
     printf("Calc%d : %d NON è un numero primo \n", *th, num); 
     check=1; 
     break; 
   }


}




else{


return 0 ; 


    }
}
/////


if (num<=n){
    if(check == 0){
        
        printf("Calc%d : %d  è un numero primo , lo invio al memorizzatore\n", *th, num); 
        write (fp, &num , sizeof(num)); 


    }


}
 else {


    return 0 ; 




 }




if(num <= n){
    num++; 


}




}




}


int main(int argc , char *argv[]){


char *fifo =  "myfifo" ;


if (argc != 2 ){
printf("Errore nell'immissione dei parametri \n ");
return -1 ; 
    } 


int error ; 
n= atoi(argv[1]); 
pthread_t t1 , t2 , t3 ; 
pthread_t *calc_arr[3] = { &t1 , &t2 , &t3 } ;  //array per l'id dei thread


if (error = mkfifo( fifo , 0666)== -1){


//    printf("Errore nella pipe fifo \n"); 
    perror(fifo);
    if (errno != EEXIST){
    return -1; 
    }






}


if ((fp = open(fifo, O_RDONLY))==-1 ){


 perror(fifo);
 //if (errno != EEXIST)
 //return -1 ; 
 return 1; 
}




int thread[]= {1,2,3}; 


for(int i = 0; i<3 ; i++ ){
if(error = pthread_create(calc_arr[i], NULL,find_prime_number,&thread[i]) != 0  ){


perror("Errore nella creazione dei thread");
exit(1);


     }


}


for (int i = 0; i < 3 ; i++){


if (error=pthread_join(*calc_arr[i], NULL )!= 0  ){
    
perror("Errore nel join dei thread ");
exit(1);
   }


}


close(fp);
printf("Terminazione dei calcolatori \n"); 
return 0 ; 


}

Memorizer.c

Code:

#include <fcntl.h>#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>


#define MAX_BUF 1024
#define MAX_PID 8


int main()
{
    int fd ; 
    int bytesread;
    char * myfifo = "myfifo";
    char buf[MAX_BUF];


    fd = open( myfifo, O_RDONLY );
   while(1)
{
    if((bytesread = read( fd, buf, MAX_BUF - 1)) > 0)
    {
        buf[bytesread] = '\0';
        printf("Received: %s\n", buf);
    }
    else
        break;
}
    close(fd);


    return 0;
}