The following program $($thread$.$c$)$ use two threads to run the function worker. Each thread runs function worker, and update the value of the global variable counter $100000$ times. This program is run two different times, The first time the output is $143012,$ and the second time is $137298($weird$).$ A reasonable explanation for the phenomenon is:

$```$

#include

#include

#include "common.h$"$

volatile int counter $=0$;

$1$nt loops;

void $*$worker$($void $*$arg$)\{$

int i;

for $(1=0$; $1$ loops; $1++)\{$

counter$++$;

$\}$

return NULL;

$\}$

int main$($int argc, char $*$argv$[])\{$

if $($argc $!=2)\{$

fprintf$($stderr$,$ "usage: threads

$")$;

exit$(1)$;

$\}$

loops $=$ atoi$($argv$[1])$;

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

printf$("$Initial value : sd

$",$ counter$)$;

Pthread$\_$create$($&pl$,$ NULL, worker, NULL$)$;

Pthread$\_$create$($sp$2,$ NULL, worker, NULL$)$;

Pthread$\_$join$($p$1,$ NULL$)$;

Pthread$\_$Join$($p$2,$ NULL$)$;

printf$("$Final value : $\%$d

$",$ counter$)$;

return $0$;

$\}$

$```$

Output

prompt$>./$thread $100000$

Initial value : $0$

Final value : $143012//$ huh??

prompt$>./$thread $100000$

Initial value : $0$

Final value : $137298//$ what the??

There is not thread synchronization, this allows to overwrite the global variable counter

The scheduler is switching process

None of the above

There are two process and when they update the value the overwrite