$(40$ points$)$ Simple C programs on fork$().$ Suppose all printf$()$ will be

followed by fflush$($stdout$)$ even if it is not presented in the code. For all the

C programs, you can assume that necessary header files are included

$(5$ points$)$ Consider the following code segments:

int main$()$

$\{$

pid$\_$t pid$1$;

pid$\_$t pid$2$;

pid$1=$ fork$()$;

pid$2=$ fork$()$;

printf$("$pid$1$:$\%$d$,$ pid$2$:$\%$d

$",$ pid$1,$ pid$2)$;

$\}$

$($a$)$ How many processes are there in total when this code finishes?

Give the answer.

$($b$)$ If one process prints "pid$1$:$51234,$ pid$2$: $51235",$ one process prints

"pid$1$:$0,$ pid$2$: $51236",$ write down other processes' pid and their

outputs.

$(15$ points$)$ Consider the following code segments:

int main$()\{$

int i $=0$;

int cnt $=10$;

for $($; i$<mn>3</mn>$; i$++)\{$

pid$\_$t pid $=$ fork$()$;

if $($pid $==0)$

printf$("\%$d

$",$ cnt$)$;

else

cnt $+=10$;

$\}$

return $0$;

$\}$

$($a$)$ Who will print the $"$cnt$",$ the child process or parent process? Why?

How many times of "printf" will this code execute? Give the answer

with explanation.

$($b$)$ Theoretically, based on Linux fork$()$ mechanism introduced in the

lecture, how many memory copies of the variable $"$cnt$"$ will there

be$?$ Explain your answer.

$($c$)$ Directly running this piece of code may produce different outputs

every time. Briefly explain why.