1. Problem: CFQ (Circular Fifo Queue)
#define N // the queue size
shared memory int CFQ[N]; // the CFQ
shared memory int nTop; // pointer to the top of the queue
shared memory int nTail; // pointer to the tail of the queue
void producer (void) {
int new_item; // a place holder for a new item
while (TRUE)
new_item = produce_item( ); // produce a new item
while (empty < 1) // wait until a space in the CFQ
{ ; } // as a “spin wait”
CFQ[nTail] = new_item; // insert the new item to the CFQ
nTail = (nTail + 1) % N; // update the tail pointer
empty = empty – 1; // empty slots is decreased by one }
void consumer (void) {
int new_item; // a place holder for a new item
while (TRUE)
while (empty > 1) // wait until at least one item in the CFQ
{ ; } // as a “spin wait”
new_item = CFQ[nTop]; // remove the first item in the CFQ
nTop = (nTop + 1) % N; // update the top pointer
empty = empty + 1; // empty slots is decreased by one
do_something (new_item); }
What are the problems (two major problems)?

2. FIRST SOLUTION Producer Process Consumer Process
#define N // Queue Size
#define NUM_REPEAT 1,000, // Number of items to be generated
semaphore MUTEX // binary semaphore
SM: a pointer to the queue in shared memory
SMnum_element = 0; // # of the random # produced to the queue
Producer Process
Consumer Process
int i; // loop counter
int new_item; // the new random #
int tail = 0; // the position for the new #
for (i=0; i < NUM_REPEAT; i++) {
new_item = rand( );
if(SMnum_element < N)
wait(MUTEX);
SM[tail] = new_item;
SMnum_element ++;
signal(MUTEX);
tail ++;
if (tail  N)
tail = 0; }
else { i--; }
int top = 0; // the position for the new #
if(SMnum_element > 0)
new_item = SM[top];
SMnum_element --;
top ++;
if (top  N)
top = 0;
FIRST SOLUTION

3. SECOND SOLUTION Producer Process Consumer Process
#define N // Queue Size
#define NUM_REPEAT 1,000, // Number of items to be generated
semaphore MUTEX // binary semaphore
semaphore EMPTY N // counting semaphore
semaphore FULL // counting semaphore
SM: a pointer to the queue in shared memory
Producer Process
Consumer Process
int i; // loop counter
int new_item; // the new random #
int tail = 0; // the position for the new #
for (i=0; i < NUM_REPEAT; i++) {
wait(EMPTY);
new_item = rand( );
wait(MUTEX);
SM[tail] = new_item;
signal(MUTEX);
tail ++;
if (tail  N)
tail = 0;
signal(FULL); }
int top = 0; // the position for the new #
wait(FULL);
new_item = SM[top];
top ++;
if (top  N)
top = 0;
signal(EMPTY);