why the kill function does not work in linux

Question

Possible Duplicate:
Child process receives parent’s SIGINT

the is my code in below

The function is after the father receive the signal of CTRL-C. the father process send signal to son1 and son2; after the son1 and son2 exit, the father process exit;

but the result does not like that; this is the answer

son1
son2
^Cheeell
the son1 id 5963
the son2 id 5964
Parent process is killed !!

who can help me, thank you before!!

#include <stdio.h>
#include <sys/signal.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>

#define SIGNAL_TO_SON1 10
#define SIGNAL_TO_SON2 12

#define FLAG_MSG_NO 0
#define FLAG_MSG_YES 1

int parent_msg = FLAG_MSG_NO;
void signal_sendToParent( int sig )
{
    printf("heeell\n");
    parent_msg = FLAG_MSG_YES;
}

int son1_flag = FLAG_MSG_NO;
void signal_handle_son1( int sig )
{
    printf("handle_son1\n");
    son1_flag = FLAG_MSG_YES;
}

int son2_flag = FLAG_MSG_NO;
void signal_handle_son2( int sig )
{
    printf("handle_son2\n");
    son2_flag = FLAG_MSG_YES;
}

int main( void )
{
    int pid1, pid2;
    if ( ( pid1 = fork() ) < 0 )
    {
        printf("erro!!!!");
        return -1;
    }

    if ( pid1  > 0 )
    {
        // in the parent
        while( ( pid2 = fork() ) == -1);
        if ( pid2 == 0 )
        {
            signal( SIGNAL_TO_SON2, signal_handle_son2 );
            printf("son2\n");
            // in the son2;
            while ( son2_flag != FLAG_MSG_YES );
            {
                printf("Child process 2 is killed by parent !!\n");
                exit(0);            
            }
        }else{  
            // setup the signal
            signal( SIGINT, signal_sendToParent );
            while ( parent_msg != FLAG_MSG_YES );
            {
                kill( pid1, SIGNAL_TO_SON1 );
                kill( pid2, SIGNAL_TO_SON2 );
                wait(0);
                printf("the son1 id %d\n", pid1 );
                printf("the son2 id %d\n", pid2 );              

                wait(0);
                int status , pid ;
                while( ( pid = waitpid( -1, &status, 0 ) )  > 0 )
                {
                    printf("child %d \n", pid );
                }
                printf("Parent process is killed !!\n");
                exit(0);
            }
        }
    }else{
        // in the son1;
        printf("son1\n");
        signal( SIGNAL_TO_SON1, signal_handle_son1 );
        while ( son1_flag != FLAG_MSG_YES );
        {
            printf("Child process 1 is killed by parent !!\n");
            exit(0);
        }
    }

    return 0;
}

@Jan: Care to elaborate? It sure looks to me like his problem is that the `SIGINT` generated by Ctrl-C is going to all three processes. — Nemo, Jan 02 '13 at 17:47
@Nemo: Yes, but if this was just closed as duplicate, it wouldn't be obvious. — Jan Hudec, Jan 02 '13 at 17:49
@Jan: It will be perfectly obvious. If another question has the exact same answer, then it is a duplicate. — Nemo, Jan 02 '13 at 17:50

score 1 · Accepted Answer · edited May 23 '17 at 12:12

1

to get what you want you must ignore SIGINT in the childs.

see this What happens to a SIGINT (^C) when sent to a perl script containing children?

In short Ctrl-C is send to all processes in the foreground group. That means your child processes get SIGINT too, they do not have a handler and get killed.

signal( SIGINT, SIG_IGN );

add in the child code, near setting the other signal handler.

edited May 23 '17 at 12:12

Community

1
1

answered Jan 02 '13 at 17:48

Alexander Atanasov

486
4
7

I would probably prefer the `setpgid` as [expained in this answer to similar question](http://stackoverflow.com/a/6804155/201725). – Jan Hudec Jan 02 '13 at 17:56
thank you very much, can you recommend some books and techniques for me to learn the linux. the command is so much. – user1943491 Jan 03 '13 at 01:56

why the kill function does not work in linux

1 Answers1