Bounded-Buffer

•         The statements

counter++;
counter--;

must be performed atomically.

•         Atomic operation means an operation that completes in its entirety without interruption.
•         The statement “count++” may be implemented in machine language as:

register1 = counter

  register1 = register1 + 1
counter = register1

• The statement “count—” may be implemented as:

register2 = counter
register2 = register2 – 1
counter = register2

• If both the producer and consumer attempt to update the buffer concurrently, the assembly language statements may get interleaved.
• Interleaving depends upon how the producer and consumer processes are scheduled.
• Assume counter is initially 5. One interleaving of statements is:

producer: register1 = counter (register1 = 5)
producer: register1 = register1 + 1 (register1 = 6)
consumer: register2 = counter (register2 = 5)
consumer: register2 = register2 – 1 (register2 = 4)
producer: counter = register1 (counter = 6)
consumer: counter = register2 (counter = 4)

• The value of count may be either 4 or 6, where the correct result should be 5.