#include #include #include #include #define BUFFSIZE $5$ sem$\_$t empty; $//$semaphore empty sem$\_$t full; $//$semaphore full int buffer$[$BUFFSIZE$]$; pthread$\_$mutex$\_$t mutex; $//$mutex lock int in $=0$; int out $=0$; int item $=0$; void$*$ producer$($void$*$ p$)\{$ for $($int i $=0$; i $<6$; i$++)\{$ sem$\_$wait$($&empty$)$; $//$wait operation on semaphore empty pthread$\_$mutex$\_$lock$($&mutex$)$; $//$lock mutex buffer$[$in$]=$ item; $//$insert the item to the buffer item $=$ item $+1$; printf$("$producer $\%$d: insert item $\%$d at$\backslash$tbuffer$[\%$d$]",*(($int$*)$p$),$ buffer$[$in$],$ in$)$; in $=($in$+1)\%$ BUFFSIZE; pthread$\_$mutex$\_$unlock$($&mutex$)$; $//$unlock mutex sem$\_$post$($&full$)$; $//$signal operation on emaphore full $\}\}$ void$*$ consumer$($void$*$ c$)\{$ for $($int i $=0$; i $<4$; i$++)\{$ sem$\_$wait$($&full$)$; pthread$\_$mutex$\_$lock$($&mutex$)$; int item$\_$removed $=$ buffer$[$out$]$; printf$("$consumer $\%$d: remove item $\%$d from buffer$[\%$d$]",*(($int$*)$c$),$ item$\_$removed, out$)$; out $=($out$+1)\%$ BUFFSIZE; pthread$\_$mutex$\_$unlock$($&mutex$)$; sem$\_$post$($&empty$)$; $\}\}$ int main$()\{$ pthread$\_$t p$[4],$ c$[6]$; $////$array p$[4]$ and c$[6]$ are used to label producers and consumers, respectively pthread$\_$mutex$\_$init$($&mutex, NULL$)$; $//$initialize mutex to unlocked sem$\_$init$($&empty, $0,$ BUFFSIZE$)$; $//$initialize semaphore empty to value of BUFFSIZE, which is $5$ sem$\_$init$($&full, $0,0)$; $//$initialize semaphore full to zero int a$[6]=\{1,2,3,4,5,6\}$; $//$keep track of the producer and consumer threads numbers for $($int i $=0$; i $<4$; i$++)\{//$create producers pthread$\_$create$($&p$[$i$],$ NULL, $($void$*)$producer$,($void$*)$&a$[$i$])$; $\}$ for $($int i $=0$; i $<6$; i$++)\{//$create consumers pthread$\_$create$($&c$[$i$],$ NULL, $($void$*)$consumer$,($void$*)$&a$[$i$])$; $\}$ for $($int i $=0$; i $<4$; i$++)\{//$main thread waits for the newly created thread to finish pthread$\_$join$($p$[$i$],$ NULL$)$; $\}$ for $($int i $=0$; i $<6$; i$++)\{//$main thread waits for the newly created thread to finish pthread$\_$join$($c$[$i$],$ NULL$)$; $\}$ pthread$\_$mutex$\_$destroy$($&mutex$)$; sem$\_$destroy$($&empty$)$; sem$\_$destroy$($&full$)$; return $0$; $\}$ a$)$ What do Lines $28$ and $42$ try to accomplish? b$)$ Why variables in$,$ out and item are defined as global variables? c$)$ How does the program ensure that a consumer does not grab an item from the buffer if the buffer is empty?