$1.$ Consider the following C program. $($For space reasons, we are not checking error return codes, so assume that all functions return normally.$)$

$$

pid$\_$t pid;

void handler$1($int sig$)\{$

$$ printf$("$B

$")$;

$$ kill$($pid$,$ SIGUSR$2)$;

$\}$

void handler$2($int sig$)\{$

$$ printf$("$C

$")$;

$$ exit$(0)$;

$\}$

int main$()\{$

$$ signal$($SIGUSR$1,$ handler$1)$;

$$ signal$($SIGCHLD$,$ handler$2)$;

$$ if $(($pid $=$ fork$())==0)\{$

$$ signal$($SIGUSR$2,$ handler$2)$;

$$ kill$($getppid$(),$ SIGUSR$1)$;

$//$ getppid$()$ returns parent$$s pid

$$ while$(1)\{\}$;

$\}$

$$ else $\{$

$$ pid$\_$t p; int status;

$$ printf$("$A

$")$;

$$ if $(($p $=$ wait$($&status$))>0)\{$

$$ printf$("$D

$")$;

$\}$