$2.(20$ points$)$ Process Synchronization

This problem involves multiple readers and one writer accessing a shared resource. When the writer wants to write, readers must wait, ensuring the writer gets priority. We will use a new API pthread$\_$cond$\_$broadcast$(\backslash$&cond$)$ to wake up all waiting threads on the conditional variable cond.

Please fill in $10$ blanks to correctly implement synchronization using mutex locks and condition variables.

$```$

#include

#include

#include

int read$\_$count $=0$; $//$ Number of active readers

int writer$\_$waiting $=0$; $//$ Is the writer waiting?

$```$

pthread$\_$mutex$\_$t read$\_$count$\_$mutex; $//$ Protects the read$\_$count variable

pthread$\_$mutex$\_$t writer$\_$mutex; $//$ Controls writer's priority and access

pthread$\_$cond$\_$t reader$\_$cond; $//$ Condition variable for readers

pthread$\_$cond$\_$t writer$\_$cond; $//$ Condition variable for the writer

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

$//$ Lock to modify read$\_$count

pthread$\_$mutex$\_$lock$(\_\_\_\_\_\_)$; $//(1)$ Lock read$\_$count$\_$mutex to access read$\_$count

$//$ Wait if the writer is waiting

while $\{//(2)$ Check if the writer is waiting

pthread$\_$cond$\_$wait$(\_\_\_,$ &read$\_$count$\_$mutex$)$; $//(3)$ Wait for the writer

$\}$

read$\_$count$++$; $//$ Increment reader count

pthread$\_$mutex$\_$unlock$($&read$\_$count$\_$mutex$)$; $//$ Unlock read$\_$count$\_$mutex

$//$ Reading section

printf$("$Reader $\%$d is reading.

$",$ id$)$;

$//$ Lock to decrement read$\_$count

pthread$\_$mutex$\_$lock$($&read$\_$count$\_$mutex$)$; $//$ Lock read$\_$count$\_$mutex

read$\_$count$--$; $//$ Decrement reader count

$//$ If no readers are active, signal the writer

if $(\_\_\_\_)\{//(4)$ Check if no readers are active

pthread$\_$cond$\_$signall ; $//(5)$ Signal the writer

$\}$

pthread$\_$mutex$\_$unlock$($&read$\_$count$\_$mutex$)$; $//$ Unlock read$\_$count$\_$mutex

return NULL;

$\}$

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

$//$ Lock to manage writer state and access

pthread$\_$mutex$\_$lock$(\_\_\_\_\_)$; $//(6)$ Lock writer$\_$mutex to access writer state

writer$\_$waiting $=1$; $//$ Mark the writer as waiting

$//$ Wait until all readers are done

pthread$\_$mutex$\_$lock$($&read$\_$count$\_$mutex$)$; $//$ Lock read$\_$count$\_$mutex

while $(\_\_\_)\{//(7)$ Check if any readers are active

pthread$\_$cond$\_$wait $,$ &read$\_$count$\_$mutex$)$; $//(8)$ Wait for readers to finish

$\}$

pthread$\_$mutex$\_$unlock$($&read$\_$count$\_$mutex$)$; $//$ Unlock read$\_$count$\_$mutex

$//$ Writing section

printf$("$Writer $\%$d is writing.

$",$ id$)$;

writer$\_$waiting $=0$; $//$ Mark the writer as not waiting

$//$ Signal waiting readers to proceed

pthread$\_$cond$\_$broadcast$(\_\_\_\_\_)$; $//(9)$ Broadcast to readers

pthread$\_$mutex$\_$unlock$(\_\_\_\_\_)$; $//(10)$ Unlock writer$\_$mutex

return NULL;

$\}$