Date: Tue, 23 Mar 1999 13:08:08 +0000 From: Mark Ovens <marko@uk.radan.com> To: hackers@freebsd.org Subject: Problem with fork() in 3.1 Message-ID: <36F79238.5FC1DA7C@uk.radan.com>
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Hi,
Firstly, my apologies if this is an inappropriate question to post
here, but I have asked in -questions and received no response and I am
completely stumped. If anyone could spare a couple of minutes to look
at this for me I would be very grateful (my learning curve is
currently flat-lining).
I have been learning about Inter Process Comms and have written the 2
progs included below. It all worked under 2.2.8 however when I u/g to
3.1-R (from the CD) it no longer works :-(.
Under 2.2.8 the output was:
% demo
RESULT! - Circumference-106.814150
%
however, under 3.1 this happens:
% demo
RESULT! -
%
The string returned from d2c doesn't appear. This happens (in 3.1)
with both the 2.2.8 compiled progs (aout) and the 3.1 compiled progs
(ELF).
If I add ``sleep(5)'' to both progs ``ps'' confirms that the exec()'d
program (d2c) is running.
Someone else posted a message to -questions with exactly the same
problem using rfork().
FWIW, as well as working under 2.2.8, these programs run properly
under SunOS 4.1.3.
BTW. I realize that this code is not good enough for real-world
applications but, as I said, I'm learning so starting simple seems
that best way.
TIA for your time.
-----file - demo.c--------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
void main()
{
int fd[2];
int df[2];
pid_t pid;
char input[BUFSIZ], result[BUFSIZ];
if (pipe(fd) < 0)
{
perror("pipe failed");
exit(EXIT_FAILURE);
}
if (pipe(df) < 0)
{
perror("pipe failed");
exit(EXIT_FAILURE);
}
if ((pid = fork()) < 0)
{
perror("fork failed");
exit(EXIT_FAILURE);
}
if (pid > 0) /* parent */
{
close(fd[0]);
close(df[1]);
read(df[0], input, BUFSIZ - 1);
if (strstr(input, "Diameter"))
write(fd[1], "34\n", 3);
read(df[0], result, BUFSIZ - 1);
fprintf(stderr, "RESULT! - %s\n", result);
close(fd[1]);
close(df[0]);
}
else
{ /* child */
if (fd[0] != STDIN_FILENO)
{
if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)
{
perror("dup2 fd[0] failed");
exit(EXIT_FAILURE);
}
}
if (df[1] != STDOUT_FILENO)
{
if (dup2(df[1], STDOUT_FILENO) !=
STDOUT_FILENO)
{
perror("dup2 df[1] failed");
exit(EXIT_FAILURE);
}
}
close(fd[1]);
close(df[0]);
if (execvp("./d2c", NULL) < 0)
{
perror("execvp failed");
exit(EXIT_FAILURE);
}
close(fd[0]); /* Don't think these are really needed
*/
close(df[1]); /* as execvp() only returns on failure
*/
/* & then exit() will be called above
*/
}
}
-----file - d2c.c----------
#include <stdio.h>
#include <stdlib.h>
#include <float.h>
#define PI 3.141592653
int main(void)
{
double circ;
char input[BUFSIZ];
printf("%s", "Diameter: ");
fflush(stdout);
fgets(input, BUFSIZ-1, stdin);
circ = atof(input) * PI;
printf("Circumference-%f\n", circ);
fflush(stdout);
return(0);
}
-----------------------------------
--
FreeBSD - The Power To Serve http://www.freebsd.org
My Webpage http://www.users.globalnet.co.uk/~markov
_______________________________________________________________
Mark Ovens, CNC Apps Engineer, Radan Computational Ltd. Bath UK
CAD/CAM solutions for Sheetmetal Working Industry
mailto:marko@uk.radan.com http://www.radan.com
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