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Full Discussion: share file descriptor between childs
Top Forums Programming share file descriptor between childs Post 302245575 by redoubtable on Friday 10th of October 2008 11:26:48 AM
Old 10-10-2008
The code you posted has a problem. But even if you solve that problem, there is another one. fork() dup()licates fd's from the parent but if you don't have some kind of synchronous read between the childs, you'll have unexpected results.

Do you really want to use multiple processes to read the same fd?

Try running this several times to see what I'm talking about:
Code:
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define CHILDS_N 5

void worker(int * fd)
{
        char buf[20];

        memset (buf, 0x0, sizeof (buf));
        read(*fd, buf, sizeof (buf)-1);
        printf ("%s\n", buf);

}


int
main ()
{
        pid_t childs[CHILDS_N];
        int fd;
        int i;
        fd = open ("Client_Files.txt", O_RDONLY);
        if (fd == -1)
                exit(1);


        for (i=0; i < CHILDS_N; i++)
        {
                childs[i] = fork();
                if (childs[i] == 0)
                {
                        worker(&fd);
                }
                else
                {
//                      printf ("parent: %d\n", getpid());
                }
        }
}

 

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LEARN ABOUT DEBIAN

empty-page

EMPTY-PAGE(1)							 ExactImage Manual						     EMPTY-PAGE(1)

NAME

       empty-page - empty page detector of the ExactImage toolkit

SYNOPSIS

       empty-page [option...] {-i | --input} input-file

       empty-page {-h | --help}

DESCRIPTION

       ExactImage is a fast C++ image processing library. Unlike many other library frameworks it allows operation in several color spaces and bit
       depths natively, resulting in low memory and computational requirements.

       empty-page counts dark pixels of a black and white image and decides with a threshold whether the page is most probably empty, and thus can
       be removed from the image processing stream.

OPTIONS

       -i file, --input file
	   Read image from the specified file.

       -m n, --margin n
	   Set width of border margin to skip. For speed reasons, the margin has to be a multiple of 8. The default is 16.

       -p x, --percentage x
	   Set fraction of permissible dark pixels. The default is 0.05 (5%).

       -h, --help
	   Display help text and exit.

EXAMPLES

	   $ empty-page -i test.tif
	   The image has 75461 dark pixels from a total of 1060992 (7.11231%).
	   non-empty

EXIT STATUS

       The exit status is 0 if the image is mostly white, 1 otherwise.

SEE ALSO

       exactimage(7)

AUTHORS

       Jakub Wilk <jwilk@debian.org>
	   Wrote this manual page for the Debian system.

       http://www.exactcode.de/site/open_source/exactimage/
	   This manual page incorporates texts found on the ExactImage homepage.

COPYRIGHT

       This manual page was written for the Debian system (and may be used by others).

       Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 or (at
       your option) any later version published by the Free Software Foundation.

       On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL-2.

empty-page							    09/09/2013							     EMPTY-PAGE(1)
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