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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

gsm_create

GSM(3)							     Library Functions Manual							    GSM(3)

NAME

       gsm_create, gsm_destroy, gsm_encode, gsm_decode -- GSM 06.10 lossy sound compression

SYNOPSIS

       #include "gsm.h"

       gsm gsm_create();

       void gsm_encode(handle, src, dst)
       gsm handle;
       gsm_signal src[160];
       gsm_frame dst;

       int gsm_decode(handle, src, dst)
       gsm handle;
       gsm_frame src;
       gsm_signal dst[160];

       void gsm_destroy(handle)
       gsm handle;

DESCRIPTION

       Gsm is an implementation of the final draft GSM 06.10 standard for full-rate speech transcoding.

       gsm_create()  initializes  a  gsm  pass	and  returns  a  'gsm'	object	which can be used as a handle in subsequent calls to gsm_decode(),
       gsm_encode() or gsm_destroy().

       gsm_encode() encodes an array of 160 13-bit samples (given as gsm_signal's, signed integral values of at least 16 bits) into a gsm_frame of
       33 bytes.  (gsm_frame is a type defined as an array of 33 gsm_bytes in gsm.h.)

       gsm_decode()  decodes  a  gsm_frame  into an array of 160 13-bit samples (given as gsm_signals), which sound rather like what you handed to
       gsm_encode() on the other side of the wire.

       gsm_destroy() finishes a gsm pass and frees all storage associated with it.

   Sample format
       The following scaling is assumed for input to the algorithm:
	  0  1				   11 12
	  S..v..v..v..v..v..v..v..v..v..v..v..v..*..*..*
       Only the top 13 bits are used as a signed input value.
       The output of gsm_decode() has the three lower bits set to zero.

RETURN VALUE

       gsm_create() returns an opaque handle object of type gsm, or 0 on error.  gsm_decode() returns -1 if the passed frame is invalid, else 0.

EXAMPLE

       #include "gsm.h"

       gsm handle;
       gsm_frame buf;
       gsm_signal sample[160];
       int cc, soundfd;

       play() {  /* read compressed data from standard input, write to soundfd */

	    if (!(handle = gsm_create())) error...
	    while (cc = read(0, (char *)buf, sizeof buf)) {
		 if (cc != sizeof buf) error...
		 if (gsm_decode(handle, buf, sample) < 0) error...
		 if (write(soundfd, sample, sizeof sample) != sizeof sample)
		      error...
	    }
	    gsm_destroy(handle);
       }

       record() {     /* read from soundfd, write compressed to standard output */

	    if (!(handle = gsm_create())) error...
	    while (cc = read(soundfd, sample, sizeof sample)) {
		 if (cc != sizeof sample) error...
		 gsm_encode(handle, sample, buf);
		 if (write(1, (char *)buf, sizeof buf) != sizeof sample)
		      error...
	    }
	    gsm_destroy(handle);
       }

BUGS

       Please direct bug reports to jutta@cs.tu-berlin.de and cabo@cs.tu-berlin.de.

SEE ALSO

       toast(1), gsm_print(3), gsm_explode(3), gsm_option(3)

																	    GSM(3)
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