In this assignment, you will be given a functioning program, called minor6.c, that simply reads user input keys and echoes them back to the screen using the producerconsumer paradigm. The single producer thread reads user input keys and adds them to the shared buffer while two consumer threads read the added keys from the buffer and echo them back to the screen. To complicate matters, each key is read and echoed by exactly one consumer thread. A shared variable, called shared_count, keeps track of the number of items in the shared buffer. While this program does work (thanks to the mutex locks and unlocks already provided), it is unfortunately very inefficient. To see just how inefficient this program is, compile the original minor6.c program (using the pthread library) and execute the program. You should type in some keys and see them echoed back on the screen in their correct order. To see the inefficiency, though, run the top command from another shell (dont just run the minor6.c program in the background and then run top, but actually open up another shell/window). Then check out the %CPU column in the top command and you should see your original minor6.c program using up a significant percentage of the CPU, which is not good. Your goal for this assignment is to modify this program to use condition variables that will drastically reduce its CPU percentage usage. Here are the details: You will modify the original minor6.c file to add two condition variables, but not change the spirit of the program other than necessary changes that are needed for how conditional variables work, including handling of spurious wakeup discussed in class. You will add two global pthread condition variables one to handle when the shared buffer is full (and therefore, nothing else can be added to the buffer until a key is removed from the buffer) and one to handle when the shared buffer is empty (and therefore, nothing can be read/echoed back to the screen until a key is added to the buffer). In the main function, you will initialize and destroy both of the condition variables. You will modify the code in the producer function to wait on and signal the appropriate condition variable(s) based on what is happening with the shared variables (i.e., the shared buffer and shared counter). Note that this will require some small changes in logic to accomplish, but you should not change the lines that work with the prod_index variable. 2 of 2 You will modify the code in the consumer function to wait on and signal the appropriate condition variable(s) based on what is happening with the shared variables (i.e., the shared buffer and shared counter). Note that this will require some small changes in logic to accomplish, but you should not change the lines that work with the cons_index variable. Be sure to run your solution along with the top command to verify that the program is more efficient (i.e., does not use nearly as much percentage of the CPU). It is required that you implement and utilize the condition variables effectively in a manner that significantly reduces the CPU utilization of this program and not gain the reduction in another way.

Here's the code:

/*

* minor6.c - using producer-consumer paradigm.

*/

#include

#include

#include

#define NITEMS 10 // number of items in shared buffer

// shared variables

char shared_buffer[NITEMS]; // echo buffer

int shared_count; // item count

pthread_mutex_t mutex; // pthread mutex

unsigned int prod_index = 0; // producer index into shared buffer

unsigned int cons_index = 0; // consumer index into shard buffer

// function prototypes

void * producer(void *arg);

void * consumer(void *arg);

int main()

{

pthread_t prod_tid, cons_tid1, cons_tid2;

// initialize pthread variables

pthread_mutex_init(&mutex, NULL);

// start producer thread

pthread_create(&prod_tid, NULL, producer, NULL);

// start consumer threads

pthread_create(&cons_tid1, NULL, consumer, NULL);

pthread_create(&cons_tid2, NULL, consumer, NULL);

// wait for threads to finish

pthread_join(prod_tid, NULL);

pthread_join(cons_tid1, NULL);

pthread_join(cons_tid2, NULL);

// clean up

pthread_mutex_destroy(&mutex);

return 0;

}

// producer thread executes this function

void * producer(void *arg)

{

char key;

printf("Enter text for producer to read and consumer to print, use Ctrl-C to exit. ");

// this loop has the producer read in from stdin and place on the shared buffer

while (1)

{

// read input key

scanf("%c", &key);

// this loop is used to poll the shared buffer to see if it is full:

// -- if full, unlock and loop again to keep polling

// -- if not full, keep locked and proceed to place character on shared buffer

while (1)

{

// acquire mutex lock

pthread_mutex_lock(&mutex);

// if buffer is full, release mutex lock and check again

if (shared_count == NITEMS)

pthread_mutex_unlock(&mutex);

else

break;

}

// store key in shared buffer

shared_buffer[prod_index] = key;

// update shared count variable

shared_count++;

// update producer index

if (prod_index == NITEMS - 1)

prod_index = 0;

else

prod_index++;

// release mutex lock

pthread_mutex_unlock(&mutex);

}

return NULL;

}

// consumer thread executes this function

void * consumer(void *arg)

{

char key;

long unsigned int id = (long unsigned int)pthread_self();

// this loop has the consumer gets from the shared buffer and prints to stdout

while (1)

{

// this loop is used to poll the shared buffer to see if it is empty:

// -- if empty, unlock and loop again to keep polling

// -- if not empty, keep locked and proceed to get character from shared buffer

while (1)

{

// acquire mutex lock

pthread_mutex_lock(&mutex);

// if buffer is empty, release mutex lock and check again

if (shared_count == 0)

pthread_mutex_unlock(&mutex);

else

break;

}

// read key from shared buffer

key = shared_buffer[cons_index];

// echo key

printf("consumer %lu: %c ", (long unsigned int) id, key);

// update shared count variable

shared_count--;

// update consumer index

if (cons_index == NITEMS - 1)

cons_index = 0;

else

cons_index++;

// release mutex lock

pthread_mutex_unlock(&mutex);

}

return NULL;

}