Process-Synchronization

(a) A certain processor provides a ‘test and set’ instruction that is used as follows:

 TEST register, flag 

This instruction atomically copies flag to register and sets flag to 1. Give pseudo-code for implementing the entry and exit code to a critical region using this instruction.

(b) Consider the following solution to the producer-consumer problem using a buffer of size 1. Assume that the initial value of count is 0. Also assume that the testing of count and assignment to count are atomic operations.

            Producer:      
                Repeat 
                         Produce an item;
                         if count = 1 then sleep;
                         place item in buffer.
                         Count = 1;
                         Wakeup(Consumer);
               Forever 

            Consumer:
               Repeat
                         if count = 0 then sleep;
                         Remove item from buffer;
                         Count = 0;
                         Wakeup(Producer);
                         Consume item;
              Forever; 

Show that in this solution it is possible that both the processes are sleeping at the same time.