27-JAN-2004

Lecture Outline

Synchronization

1. Independent Vs Cooperating Processes
   We will deal with cooperating processes in this course
   
2. Why support cooperative processes?
   - Share resources
   - Construct System in modular fashion
   - Do things faster
   
3. Cooperating requires synchronization?
   - e.g. Two processes sharing account balance
          void deposit (int amount) {
                    balance += amount;
          }
   - Implemented as sequence of assembly instructions
   - What happens if two processes make deposit at same time?
   - What will be the final balance?
   - Race condition
4. Avoiding race conditions
   - Critical Section
   - Atomic operations
   
5. Critical Sections
   Requirements (Conditions to be satisfied)
   - Mutual Exclusion
   - Progress (Deadlock-free)
   - Bounded (Starvation-free)
   Desirable Properties
   - Efficient
   - Fair
   - Simple
   
6. Solutions to Critical Section Problem
   - Attempt 1 (using a boolean lock)
   - Attempt 2 (using 2 boolean locks, one for each process)
   - Attempt 3 (using turn)
   - Final Attempt (Combining attempt 2 and 3)
   
7. Locks
   - lock.acquire()
   - lock.release()