1. COMS 414 - Prelim 1 Review Session
Multiprocessing and Synchronization

2. Prelim 1
There are many, many resources available for your Prelim 1 needs: (presented in random order)
Your notes!
The book and its website
FA2000 Homeworks/Solutions
FA2000 Prelim 1 review slides
SP2001 Lecture notes
Newsgroup
Plenty of office hours!
Additional support by appointment

3. Before we begin … Any questions from the CS314 review session?
Register set, stack, heap
Program counter
Interrupts / exceptions
Interrupt priority levels
Programmable I/O vs. DMA
Polling
Memory protection (base/limit)

4. Multitasking What is a:
Process or Task?
Thread?
What is the difference between a program and a process?
What is in the PCB?
Differences between O/S processes and user processes?
Differences between user-level threads and kernel-level threads?

5. Multitasking What is kernel space? What is user space?
What is a system call?
What is a context switch?
What states may a process be in?
How do processes go between states?
What is a race condition?

6. Synchronization What is a critical section?
What are the three requirements for protection of a critical section?
What is busy waiting?
What are atomic instructions?
What is a semaphore?

7. Synchronization
Three levels of abstraction for concurrent programming:
Hardware instructions
O/S functions
Programming language constructs

8. Vivek Presents … Classic Synchronization Problems
Monitors, Condition Variables and Language Support
Deadlocks, Prevention and Avoidance

9. Monitors What is a monitor? What are condition variables?
Differentiate between semaphores and condition variables.

10. Synchronization Problems
Bounded buffer problem
Readers writers problem
Dining philosophers problems

11. Deadlock
What is a deadlock?
Necessary conditions for deadlock ?

12. Deadlocks
R R2 . P1 P2 P3 R3

13. Deadlocks
R R2 . . P1 P2 P3 . R3 P4

14. Deadlock Prevention
Make sure that one of the necessary conditions does not hold
-- Mutual exclusion
-- Hold and Wait
-- No Pre Emption
-- Circular Wait

15. Deadlock Avoidance What is it? What is Safe State? Safety Check?
Bankers Algorithm