Suppose we have a program as follows:

#include

#include

int i $=0$;

void $*$do$\_$stuff$($void $*$arg$)\{$

i$++$;

return NULL;

$\}$

int main$()\{$

pthread$\_$t tid$1,$ tid$2$;

pthread$\_$create$($&tid$1,$ NULL, do$\_$stuff, NULL$)$;

pthread$\_$create$($&tid$2,$ NULL, do$\_$stuff, NULL$)$;

pthread$\_$join$($tid$1,$ NULL$)$;

pthread$\_$join$($tid$2,$ NULL$)$;

printf$("\%$d

$",$ i$)$;

return $0$;

$\}$

Recall that because iis a global variable, i$++$; will compile to something like this:

$400728$: $8$b $042540106000$ mov $0$x$601040,\%$eax

$40072$f: $83$ c$001$ add $$0$x$1,\%$eax

$400732$: $89042540106000$ mov $\%$eax,$0$x$601040$

A$.(8$ points$)$ What are all possible outputs of this program? For each output, explain how the kernel

could interleave execution of the two child threads to produce it$.$

Initials: $14$

Suppose we alter do stuff to look as follows:

void $*$do$\_$stuff$($void $*$arg attribute $(($unused$)))\{$

int a;

for $($a $=0$; a $<1000$; a$++)$

i$++$;

return NULL;

$\}$

Because the code is not optimized, there will be one load$-$increment$-$store sequence per iteration of the

loop.

B$.(6$ points$)$ For each number, tell whether or not our program could output it$,$ and briefly explain why

or why not.

$2000$

$1500$

$2$

$1$