Semaphores

Goal

• Understand how to implement Acquire and Release for user programs and understand semaphores

Reading Assignments

• MOS 2.3.4-2.3.6

Discussion Topics

• Using pseudo-code to show how to implement Block and Unblock system calls.  Your solution should work on multiprocessors.
• The classical definition of P (or Down) and V (or Up) in pseudo-code is:
  P(s) {
      while (s <= 0)
      ;
      s--;
  }
  
  V(s) {
      s++;
  }
  This definition assumes that the modifications to semaphore s are executed indivisibly. Real implementations do not implement semaphore primitives this way, since busy wait is inefficient.  Show your idea in pseudo-code how to implement the semaphore primitives using minimal busy wait.  You are allowed to use the Block and Unblock system calls above.  Note that your solution should work on multiprocessors.