$.$ Many current language specifications, such as for C and C$++,$ are inadequate for multithreaded programs. This can have an impact on compilers and the correctness of code, as this program illustrates. Consider the following declarations and function definition:

#include

#include

#include

#include

int global$\_$positives $=0$;

typedef struct list $\{$ struct list $*$next; double val;

$\}*$ list;

void $*$count$\_$positives$($struct list $*$l$)\{$ struct list $*$p;

for$($p $=$ l; p$->$next ; p $=$ p $->$ next$)$

$\{$

if $($p $->$ val $>0\mathrm{.}0)$

$++$global$\_$positives;

$\}$

$\}$

Now consider the case in which thread A performs.

count$\_$posivites$()$;

While thread B performs:

$++$global$\_$positives;

a$)$ What does the function do$?$

b$)$ The C language only addresses single threaded execution. Does the use of two parallel threads create any problems or potential problems?