process sync using sigusr1 and sigusr2

Question

i am writing a producer process to write a block of data to a file, and a consumer process to read the same block, but the below code gets stuck in an infinite loop, now from my side i think i am having a problem in the consumer process implementation!!

void wakeup() { ; };
unsigned int sleep ( unsigned int timer ) 
{
   if (sigset(SIGALRM, wakeup)==-1) {
     perror("sigset"); return 1;
}

        (void)alarm( timer );
        (void)pause();
        return 0;
        }



int main(void) {
int fd, n, i, SomeInt, DataRead;
pid_t pid, ppid; 
char buf[4];
char *buf2;
int x=0;
if((fd=open("/tmp/data_file", O_APPEND|O_CREAT, 0640)) <0) exit(1);
sigset(SIGTERM,SIG_IGN);/* signal */   ; sigset(SIGINT,SIG_IGN); /* signal */ 
pid=fork(); 
switch (pid) { 
    case -1: { perror("FORK"); exit(1); } break;
    case 0: /* child process - Producer */ 
        sigset(SIGUSR1,wakeup);   
        sighold(SIGUSR1);       /* block / hold signals SIGUSR1 until sigpause*/ 

   FILE *file = fopen ("binary.txt", "r");
    while (!feof(file))
     {    n = (int)(getpid()%256); 
          srand((unsigned)n);
          sleep(rand() %5);
          for( x=0; x<=4;x++)
             fscanf (file, "", buf[x]);

         write(fd, buf,sizeof(buf)); 
        ppid=getppid(); 
        kill(ppid, SIGUSR2);   
        sigpause(SIGUSR1); 

      }

   fclose(file);
   fflush(stdin);


break;


default:    /* -parent code - Consumer */ 


                sigset(SIGUSR2,wakeup);
        sighold(SIGUSR2);       /* block / hold signals SIGUSR2 until sigpause*/ 
        for (i=0; i<=100; i++) { 
            /* sleep a random amount of time */ 
            n = (int)(getpid()%256); 
            srand((unsigned)n); 
            sleep(rand() %5);
            sigpause(SIGUSR2); /* pause(); */ 
            /* reads a character from file */ 
            read(fd, buf,sizeof(buf)); 
            fprintf(stderr,"Consumer PID=%d value=%d\n",getpid(),atoi(buf));
            kill(pid, SIGUSR1) ;
} 
break; 
} 
exit(0); 
}

Answer 1

the below code gets stuck in an infinite loop, now from my side i think i am having a problem in the consumer process implementation

One problem is in the producer process, where you programmed an infinite loop as follows:

 while (!feof(file))
 {    ...
      for (x=0; x<=4; x++)
           fscanf(file, "", buf[x]);
      ...
 }

With the empty format string you manage to read nothing from the file, and thus never reaching feof(file) .

Among other serious problems you have are your indentation "style" (as AShelly mentioned) and the lack of error checking (eg of fopen() and write() ).