[Solved] Problem with fork() while reading files Post: 302811811

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Top Forums Programming [Solved] Problem with fork() while reading files Post 302811811 by pfpietro on Friday 24th of May 2013 09:05:50 AM

05-24-2013

Registered User

[Solved] Problem with fork() while reading files

Good evening everyone. I have my finals and I'm facing a problem:

I have a for cycle that is supposed to fork 2 children but somehow it forks only the first one.

What am I doing wrong ?

Code:

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <signal.h>
#define MAX 255

// ./conta_caratteri c1 c2 N file_in file_out //

void contare(char *file);
int n,a, status, terminazione;
char *file_in, *file_out;

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


int send, pid[MAX],fd, i;
file_in = argv[1];

i=0;
for(i=0; i<2; i++);
{
    pid[i]=fork();
    if ( pid[i] == 0 )
        {
        contare(file_in);
        exit(0);
        }
    if ( pid > 0 )
    {
        printf(" Creato figlio %d \n ", pid[i]);
        for ( i=0; i<2; i++ )
            {
            terminazione = wait(&status);
            if (terminazione == 0)
            printf("Figlio non terminato bene. %d \n", status);
            else
            printf("Figlio %d terminato %d \n", terminazione, status);
            }    
    }    
}




return;
}


void contare(char *file)
{
printf("%c \n\n", a);

int fd = open(file, O_RDONLY);
if ( fd < 0 )
    {
    perror("Failure nell apertura");
    exit(EXIT_FAILURE);
    }
else
    printf("File %s aperto. \n", file_in);
    close(fd);
return;
}

So, the program is pretty simple: I'm supposed to call the program ./program file_name
and its supposed to fork 2 children that will open the same file (argv[1] = file_name ). But as far as I can see I'm missing something because the program forks only one child.

Help ?

pfpietro

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LEARN ABOUT NETBSD

pthread_atfork

PTHREAD_ATFORK(3)					   BSD Library Functions Manual 					 PTHREAD_ATFORK(3)

NAME

     pthread_atfork -- register handlers to be called when process forks

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <pthread.h>

     int
     pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void));

DESCRIPTION

     The pthread_atfork() function registers the provided handler functions to be called when the fork(2) function is called.  Each of the three
     handlers is called at a different place in the fork(2) sequence.  The prepare handler is called in the parent process before the fork hap-
     pens, the parent handler is called in the parent process after the fork has happened, and the child handler is called in the child process
     after the fork has happened.  The parent and child handlers are called in the order in which they were registered, while the prepare handlers
     are called in reverse of the order in which they were registered.

     Any of the handlers given may be NULL.

     The intended use of pthread_atfork() is to provide a consistent state to a child process from a multithreaded parent process where locks may
     be acquired and released asynchronously with respect to the fork(2) call.	Each subsystem with locks that are used in a child process should
     register handlers with pthread_atfork() that acquires those locks in the prepare handler and releases them in the parent handler.

RETURN VALUES

     The pthread_atfork() function returns 0 on success and an error number on failure.

ERRORS

     The following error code may be returned:

     [ENOMEM]		Insufficient memory exists to register the fork handlers.

SEE ALSO

     fork(2)

STANDARDS

     The pthread_atfork() function conforms to IEEE Std 1003.1c-1995 (``POSIX.1'').

HISTORY

     The pthread_atfork() function first appeared in NetBSD 2.0.

CAVEATS

     After calling fork(2) from a multithreaded process, it is only safe to call async-signal-safe functions until calling one of the exec(3)
     functions.  The pthread_*() functions are not async-signal-safe, so it is not safe to use such functions in the child handler.

BUGS

     There is no way to unregister a handler registered with pthread_atfork().

BSD
								 February 12, 2003							       BSD