fork multiple shells

Hi,

i was trying to play with fork,exec and signal for spawning multiple
new shells, but it seems that i'm doing blunder somewhere.

<sample code>


1 /*
2 * The idea is to fork multpile(equal to $ULIMIT) childs
3 * and replace their images with process:csh
4 * during this the parent will save the pids of all the spawned
childs
5 * till count reaches $ULIMIT and will start killing all the
6 * childs.
7 */
8
9 /*
10 * The implementation to store the PIDs of all the child
11 * forked here is using an array
12 */
13
14 #include <sys/types.h>
15 #include <unistd.h>
16 #include <stdio.h>
17 #include <signal.h>
18 #include <stdlib.h>
19 #include <errno.h>
20
21 #define ULIMIT 2
22 int main(void){
23 pid_t pid;
24 int count;
25 int ret;
26 int childpids[ULIMIT];
27 for(count = 0; count < ULIMIT; count++){
28 pid = vfork();
29 if(pid < 0){
30 perror("fork error");
31 exit(1);
32 }
33 if(pid == 0){ /*In child,Replace it with a new process: csh*/
34 ret = execlp("csh", "/bin/csh",(char *)0);
35 if(ret){
36 fprintf(stderr,"could not exec csh for count: %d\n:",count);
37 exit(1);
38 }
39 }
40 else{ /*In Parent*/
41 printf("child's pid is %d\n",pid);
42 printf("count reached = %d\n",count);
43 childpids[count] = pid;
44 }
45 }
/* Now start killing all the childs(c- shells)*/
46 while(--count){
47 if(kill(SIGKILL,childpids[count]) == -1){
48 perror("kill error");
49 exit(1);
50 }
51 }
52 kill(SIGKILL,childpids[count]);
53 exit(EXIT_SUCCESS);
54 }

<sample code>

root@localhost ]# gcc -Wall -Werror fork-csh.c -o fork-csh

[root@localhost ]# ./fork-csh
# child id is 14318

[1]+ Stopped ./fork-csh

[root@localhost ]# ps -el|grep csh|grep -v grep
4 T 0 14317 12639 0 75 0 - 344 finish pts/1 00:00:00 fork-csh
4 Z 0 14318 14317 0 80 0 - 0 do_exi pts/1 00:00:00 csh <defunct>
4 T 0 14319 14317 0 75 0 - 421 finish pts/1 00:00:00 csh

instead of my logic working i get "zombie process"
please let me know how to let my logic working.

~amit

In article
<bfc63900-ab95-4e49-9ab0-9c938dc37712@v23g2000pro.googlegroups.com>,
"amit4g@gmail.com" <amit4g@gmail.com> wrote:
[color=blue]
> Hi,
>
> i was trying to play with fork,exec and signal for spawning multiple
> new shells, but it seems that i'm doing blunder somewhere.
>
> <sample code>[/color]

The child csh is making itself the foreground process on your terminal.
This is causing fork-csh to be treated as a background process. You
apparently have "stty tostop" enabled on your terminal, so when fork-csh
tries to print "count reached", it's stopped, and it never gets to the
kill loop.
[color=blue]
>
>
> 1 /*
> 2 * The idea is to fork multpile(equal to $ULIMIT) childs
> 3 * and replace their images with process:csh
> 4 * during this the parent will save the pids of all the spawned
> childs
> 5 * till count reaches $ULIMIT and will start killing all the
> 6 * childs.
> 7 */
> 8
> 9 /*
> 10 * The implementation to store the PIDs of all the child
> 11 * forked here is using an array
> 12 */
> 13
> 14 #include <sys/types.h>
> 15 #include <unistd.h>
> 16 #include <stdio.h>
> 17 #include <signal.h>
> 18 #include <stdlib.h>
> 19 #include <errno.h>
> 20
> 21 #define ULIMIT 2
> 22 int main(void){
> 23 pid_t pid;
> 24 int count;
> 25 int ret;
> 26 int childpids[ULIMIT];
> 27 for(count = 0; count < ULIMIT; count++){
> 28 pid = vfork();
> 29 if(pid < 0){
> 30 perror("fork error");
> 31 exit(1);
> 32 }
> 33 if(pid == 0){ /*In child,Replace it with a new process: csh*/
> 34 ret = execlp("csh", "/bin/csh",(char *)0);
> 35 if(ret){
> 36 fprintf(stderr,"could not exec csh for count: %d\n:",count);
> 37 exit(1);
> 38 }
> 39 }
> 40 else{ /*In Parent*/
> 41 printf("child's pid is %d\n",pid);
> 42 printf("count reached = %d\n",count);
> 43 childpids[count] = pid;
> 44 }
> 45 }
> /* Now start killing all the childs(c- shells)*/
> 46 while(--count){
> 47 if(kill(SIGKILL,childpids[count]) == -1){
> 48 perror("kill error");
> 49 exit(1);
> 50 }
> 51 }
> 52 kill(SIGKILL,childpids[count]);
> 53 exit(EXIT_SUCCESS);
> 54 }
>
> <sample code>
>
> root@localhost ]# gcc -Wall -Werror fork-csh.c -o fork-csh
>
> [root@localhost ]# ./fork-csh
> # child id is 14318
>
> [1]+ Stopped ./fork-csh
>
> [root@localhost ]# ps -el|grep csh|grep -v grep
> 4 T 0 14317 12639 0 75 0 - 344 finish pts/1 00:00:00 fork-csh
> 4 Z 0 14318 14317 0 80 0 - 0 do_exi pts/1 00:00:00 csh <defunct>
> 4 T 0 14319 14317 0 75 0 - 421 finish pts/1 00:00:00 csh
>
> instead of my logic working i get "zombie process"
> please let me know how to let my logic working.
>
> ~amit[/color]

--
Barry Margolin, [email]barmar@alum.mit.edu[/email]
Arlington, MA
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*** PLEASE don't copy me on replies, I'll read them in the group ***