#Output using signals

1 messages · Page 1 of 1 (latest)

ruby heart
# 
#include <stdio.h>
#include <unistd.h>
#include <signal.h>

int childpid;

void handler(int signum) {
    printf("A\n");
    kill(childpid,SIGCONT);
}

int main() {
    int waitReturnPid;
    signal(SIGCHLD, handler);

    childpid = fork();

    if (childpid == 0) {
        sleep(1);
        raise(SIGTSTP);
        printf("B\n");
    } else if (childpid > 0) {
        wait(NULL);
        printf("C\n");
    }
}

Why is the output here
B
A
C
shouldnt it be
A
B
C
? i really dont get it please someone explain

scarlet trenchBOT
# ruby heart ```c #include <stdio.h> #include <unistd.h> #include <signal.h> int childpid; ...

Detected code, here are some useful tools:

Formatted code 
#include<stdio.h> #include<unistd.h> #include<signal.h> int childpid;
void handler(int signum) {
  printf("A\n");
  kill(childpid, SIGCONT);
}
int main() {
  int waitReturnPid;
  signal(SIGCHLD, handler);
  childpid = fork();
  if (childpid == 0) {
    sleep(1);
    raise(SIGTSTP);
    printf("B\n");
  }
  else if (childpid > 0) {
    wait(NULL);
    printf("C\n");
  }
}
#

<@&987246683568103514> please have a look, thanks.

scarlet trenchBOT
#

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ruby heart
#

like why does it send the signal first

#

"kill"

#

in handler function

solemn flax
#

it's a race conditon based on OS and it's scheduler

#

I ran your code and got ```
B
A
A
A
C

#

and then I ran your code somewhere else and got ```
A
A
B
A
C

#

If you want to get your desired output you'll need to do some synchronization between the parent and child (at least that's what I think from my very limited knowledge of C)

ruby heart