1. Deadlocks
Definition
A set of processes is in a Deadlock state when every process in the set is waiting for an event that can only be caused by another process in the set.

2. Four Necessary Conditons
Mutual exclusion
Hold and Wait
No preemption
Circular Wait

3. System Resource Allocation Graph
A Directed Graph
Vertices:
processes (p) in the system, or
resource types (r) in the system.
Edges:
(p,r) is the request edge, and
(r,p) is the assignment edge.

4. Handling Deadlocks
Prevention
Avoidance
Recovery

5. Deadlock Prevention
Must ensure that (at least) one of the four necessary conditions CAN NOT occur
Mutual exclusion
Hold and Wait
No preemption
Circular Wait

6. Deadlock Avoidance
Require enough information to ensure a Safe Sequence and a Safe State.
Each process must declare its Maximum Need.
Banker’s Algorithm