COMS 414 Prelim 1 Review Session

1
COMS 414 - Prelim 1 Review Session

• Multiprocessing and Synchronization
• Sunny(srg8_at_cornell.edu)
• Vivek(vu22_at_cornell.edu)

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
R1 R2
13
Deadlocks
R1 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