GATE | GATE CS 1999 | Question 68

[5 Marks question]

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.


Answer:

Explanation:

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