Consider the following solution to the producer-consumer synchronization problem. The shared buffer size is . Three semaphores empty, full and mutex are defined with respective initial values of 0, and 1. Semaphore empty denotes the number of available slots in the buffer, for the consumer to read from. Semaphore denotes the number of available slots in the buffer, for the producer to write to. The placeholder variables, denoted by P, Q, R, and S, in the code below can be assigned either empty or full. The valid semaphore operations are: wait ( ) and signal ( ). Producer: Consumer: do {         wait (P) ;         wait (mutex) ;         //Add item to buffer         signal (mutex) ;         signal (Q) ; } while (1) ; do {          wait (R) ;          wait (mutex) ;          //Consume item from buffer          signal (mutex) ;          signal (S) ; } while (1) ;   Which one of the following assignments to P, Q, R and S will yield the correct solution?

Option 3 : P: full, Q: empty, R: empty, S: full

The correct answer is option 3.

Concept:

Given data,

Empty = 0

Full = N

Mutex = 1

Because the value of the empty semaphore is 0, you cannot wait for the empty semaphore on the first try.

Note: 

The number of filled slots is represented by an empty semaphore, therefore the producer process must deal with both empty and mutex semaphores. The number of empty slots in a full semaphore is the same as the number of empty slots in a mutex semaphore, so consumer processes must deal with both full and mutex semaphores.

Option 1: 

It results in starvation. It is starvation is the problem that occurs when high-priority processes keep executing and low priority processes get blocked for an indefinite time. Here Producer and consumer process is not allowed. 

Option 2:

results in starvation. It producer at P condition blocks the process that there are no items to give and R conditions blocks that there is no item to consume because it is already full it means something blocking high-priority processes keep executing and low priority processes get blocked for an indefinite time.

Option 4:

Because the number of filled slots is originally 0 (as indicated by an empty semaphore), the consumer process is unable to consume. As a result, its implementation is flawed.

Option 3: P: full, Q: empty, R: empty, S: full is ensure deadlock-free and starvation-free implementation.

P: full, Q: empty, R: empty, S: full

Empty = 0

Full = N

Mutex = 1

Hence the correct answer is P: full, Q: empty, R: empty, S: full.