CODEWITHSUNDEEP
cprocesspipekillwaitpid
user5574376
user5574376

Reputation: 391

Will exit the program automatically close the pipe?

Say I create a pipe between child and parent process and the child process ends normally, will child process's pipes been closed automatically?

Also, If the child process also has a child process and the child process ends with a segmentation fault, will it also kill my grandchild process? I mean remove it from the process table(I don't need to wait for it).

EDIT: For example for the following code I generate a segmentation fault in the child process and try to wait for it in the parent process. After I run the program, waitpid return -1, but when I check WIFEXITED(status) it seems like the child process program exit normally. And I got a

Killing child process failed: No such process

error try to kill my grandchild process. I wonder if this is because segmentation fault automatically close both child and grandchild process?

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>


int main( void ) {

    pid_t childpid;
    int ends[ 2 ];
    pipe( ends );
    if ( ( childpid = fork() ) == -1 ) {
        perror( "fork failed" );
        exit( 0 );
    }
    if( childpid == 0 ) {
        pid_t cpid;
        if ( ( cpid = fork() ) == -1 ) {
            perror( "fork failed" );
            exit( 0 );
        }
        if ( cpid == 0 ){
            while(1);
        }   
        else{
            printf("cpid is : %d\n",cpid);
            char msg[32];
            sprintf( msg, "%d", cpid );
            printf("cpid con is : %s\n", msg);
            if( write( ends[ 1 ], msg, 32 ) == -1 ) {
                perror( "Write failed" );
                exit( 0 );
            }
            char *s = NULL;
            *s = 15;
            while(1);
        }
    }
    else{
        printf("childpid is : %d\n",childpid);
        char msg[ 32 ];
        int cpid;
        if( read( ends[0], msg,32 ) == -1 ) {
            perror("read failed");
            exit( 0 ); 
        }
        cpid = atoi( msg );
        int status;
        while(1) {
            if ( waitpid( childpid, &status, WNOHANG ) == -1 ) {
                //printf( "%d\n", WIFEXITED(status) );
                if ( kill( cpid, 9 ) == -1 ) {
                    perror( "Killing child process failed" );
                    exit( 0 );
                }
                /*if ( kill( cpid, 9 ) == -1 ) {
                    perror( "Killing child process failed" );
                    exit( 0 );
                }*/

            }
        }
    }
    return 0;
}

Upvotes: 3

Views: 5036

Answers (1)

Petr Skocik
Petr Skocik

Reputation: 60056

The OS will close all the filedescriptors associated with the process that has died or exited. If that closes the last filedescriptor pointing to a pipe's read end, then writes to the write end will start generating SIGPIPEs (fds are ref-counted references to vnode entity behind them).

If a parent dies, its child will be reparented to init. init will wait on it. (Grandparents can't wait on grandchildren anyhow).

Upvotes: 8

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