How and why to implement a critical section?

Why: to prevent race conditions.

1. Two or more processes accessing the same memory loc AND
2. At least one of the processes is writing to it.

Properties needed:

1. Mutual Exclusion
   • At most one process in CS
   • To prove using contradiction: show impossible for $\geq 2$ processes in CS
2. Progress
   • If both processes are not in CS, then one of them can go into CS when it needs to.
3. No starvation
   • If one process is in CS and assuming it eventually leaves, the other processes can enter CS

Peterson’s algorithm

Lamport’s bakery algorithm