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Question of Reader and Writer problem

What should be the values of blanks 1, 2, 3 to synchronization classical reader and writer algorithm?

(a) up(mutex), up(mutex), W = 1.

(b) down(mutex), up(mutex), W = 1.

(c) down(mutex), up(mutex), R >= 1 or W = 1.

(d) up(mutex), up(mutex), R >= 1 or W = 1.

Answer:

Option d is correct.

Explanation: 

For 1 

When W == 1 condition satisfy that mean one writer is already in the database so, we have no up(mutex) again and go back. 

So, the answer is up(mutex).

For 2 

When W == 1 not satisfies then the writer is not in the database. So, the reader can go inside the database and increase R = R + 1. And up the mutex i.e, up (mutex). 

So, the answer is up(mutex).

For 3

In what condition writer up (mutex) and go back to the previous statement. Obviously when more than one reader or one writer is inside the database.

So, condition will be R >= 1 or W = 1.

So, option d is correct.